livepatch,module: Remove .klp.arch and module_disable_ro()

PATCH Superseded Josh Poimboeuf 4 participants 23 messages Apr 25, 2020 – Apr 28, 2020

Subsystems (7)

Documentation x86 s390 User-mode Linux (UML) +3 more subsystems

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Josh Poimboeuf

author

2020-04-25 11:08 UTC #0 lore raw

v3 cover livepatch,module: Remove .klp.arch and module_disable_ro()

v3:
- klp: split klp_write_relocations() into object/section specific functions [joe]
- s390: fix plt/got writes [joe]
- s390: remove text_mutex usage [mbenes]
- x86: do text_poke_sync() before releasing text_mutex [peterz]
- split x86 text_mutex changes into separate patch [mbenes]

v2:
- add vmlinux.ko check [peterz]
- remove 'klp_object' forward declaration [mbenes]
- use text_mutex [jeyu]
- fix documentation TOC [jeyu]
- fix s390 issues [mbenes]
- upstream kpatch-build now supports this (though it's only enabled for Linux >= 5.8)

These patches add simplifications and improvements for some issues Peter found six months ago, as part of his non-writable text code (W^X) cleanups.

Highlights:

- Remove the livepatch arch-specific .klp.arch sections, which were used to do paravirt patching and alternatives patching for livepatch replacement code.

- Add support for jump labels in patched code.

- Remove the last module_disable_ro() usage.

For more background, see this thread:

https://lkml.kernel.org/r/20191021135312.jbbxsuipxldocdjk@treble

This has been tested with kpatch-build integration tests and klp-convert selftests.

Josh Poimboeuf (7):
livepatch: Disallow vmlinux.ko
livepatch: Apply vmlinux-specific KLP relocations early
livepatch: Prevent module-specific KLP rela sections from referencing
vmlinux symbols
s390: Change s390_kernel_write() return type to match memcpy()
livepatch: Remove module_disable_ro() usage
module: Remove module_disable_ro()
x86/module: Use text_mutex in apply_relocate_add()

Peter Zijlstra (3):
livepatch: Remove .klp.arch
s390/module: Use s390_kernel_write() for late relocations x86/module: Use text_poke() for late relocations

 Documentation/livepatch/module-elf-format.rst |  15 +-
 arch/s390/include/asm/uaccess.h               |   2 +-
 arch/s390/kernel/module.c                     | 147 +++++++++------
 arch/s390/mm/maccess.c                        |   9 +-
 arch/um/kernel/um_arch.c                      |  16 ++
 arch/x86/kernel/Makefile                      |   1 -
 arch/x86/kernel/livepatch.c                   |  53 ------
 arch/x86/kernel/module.c                      |  43 ++++-
 include/linux/livepatch.h                     |  17 +-
 include/linux/module.h                        |   2 -
 kernel/livepatch/core.c                       | 177 +++++++++++-------
 kernel/module.c                               |  23 +--
 12 files changed, 277 insertions(+), 228 deletions(-)
 delete mode 100644 arch/x86/kernel/livepatch.c

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:08 UTC #1 lore raw

PATCH v3 1/10 livepatch: Disallow vmlinux.ko

This is purely a theoretical issue, but if there were a module named vmlinux.ko, the livepatch relocation code wouldn't be able to distinguish between vmlinux-specific and vmlinux.o-specific KLP relocations.

If CONFIG_LIVEPATCH is enabled, don't allow a module named vmlinux.ko.

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Miroslav Benes <[email protected]>

---
 kernel/livepatch/core.c | 5 +++++
 1 file changed, 5 insertions(+)

kernel/livepatch/core.c +5 -0

index c3512e7e0801..40cfac8156fd 100644
@@ -1139,6 +1139,11 @@ int klp_module_coming(struct module *mod)
 	if (WARN_ON(mod->state != MODULE_STATE_COMING))
 		return -EINVAL;
 
+	if (!strcmp(mod->name, "vmlinux")) {
+		pr_err("vmlinux.ko: invalid module name");
+		return -EINVAL;
+	}
+
 	mutex_lock(&klp_mutex);
 	/*
 	 * Each module has to know that klp_module_coming()

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:09 UTC #2 lore raw

PATCH v3 2/10 livepatch: Apply vmlinux-specific KLP relocations early

In reply to Josh Poimboeuf

KLP relocations are livepatch-specific relocations which are applied to a KLP module's text or data. They exist for two reasons:

1) Unexported symbols: replacement functions often need to access unexported symbols (e.g. static functions), which "normal" relocations don't allow.

2) Late module patching: this is the ability for a KLP module to bypass normal module dependencies, such that the KLP module can be loaded *before* a to-be-patched module. This means that relocations which need to access symbols in the to-be-patched module might need to be applied to the KLP module well after it has been loaded.

Non-late-patched KLP relocations are applied from the KLP module's init function. That usually works fine, unless the patched code wants to use alternatives, paravirt patching, jump tables, or some other special section which needs relocations. Then we run into ordering issues and crashes.

In order for those special sections to work properly, the KLP relocations should be applied *before* the special section init code runs, such as apply_paravirt(), apply_alternatives(), or jump_label_apply_nops().

You might think the obvious solution would be to move the KLP relocation initialization earlier, but it's not necessarily that simple. The problem is the above-mentioned late module patching, for which KLP relocations can get applied well after the KLP module is loaded.

To "fix" this issue in the past, we created .klp.arch sections:

.klp.arch.{module}..altinstructions
.klp.arch.{module}..parainstructions

Those sections allow KLP late module patching code to call apply_paravirt() and apply_alternatives() after the module-specific KLP relocations (.klp.rela.{module}.{section}) have been applied.

But that has a lot of drawbacks, including code complexity, the need for arch-specific code, and the (per-arch) danger that we missed some special section -- for example the __jump_table section which is used for jump labels.

It turns out there's a simpler and more functional approach. There are two kinds of KLP relocation sections:

1) vmlinux-specific KLP relocation sections

.klp.rela.vmlinux.{sec}

These are relocations (applied to the KLP module) which reference unexported vmlinux symbols.

2) module-specific KLP relocation sections

.klp.rela.{module}.{sec}:

These are relocations (applied to the KLP module) which reference unexported or exported module symbols.

Up until now, these have been treated the same. However, they're inherently different.

Because of late module patching, module-specific KLP relocations can be applied very late, thus they can create the ordering headaches described above.

But vmlinux-specific KLP relocations don't have that problem. There's nothing to prevent them from being applied earlier. So apply them at the same time as normal relocations, when the KLP module is being loaded.

This means that for vmlinux-specific KLP relocations, we no longer have any ordering issues. vmlinux-referencing jump labels, alternatives, and paravirt patching will work automatically, without the need for the .klp.arch hacks.

All that said, for module-specific KLP relocations, the ordering problems still exist and we *do* still need .klp.arch. Or do we? Stay tuned.

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Peter Zijlstra (Intel) <[email protected]>

---
 include/linux/livepatch.h |  14 ++++
 kernel/livepatch/core.c   | 134 +++++++++++++++++++++++---------------
 kernel/module.c           |  10 +--
 3 files changed, 103 insertions(+), 55 deletions(-)

include/linux/livepatch.h +14 -0

index e894e74905f3..c4302e9a5905 100644
@@ -234,6 +234,11 @@ void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor);
 struct klp_state *klp_get_state(struct klp_patch *patch, unsigned long id);
 struct klp_state *klp_get_prev_state(unsigned long id);
 
+int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
+			     const char *shstrtab, const char *strtab,
+			     unsigned int symindex, unsigned int secindex,
+			     const char *objname);
+
 #else /* !CONFIG_LIVEPATCH */
 
 static inline int klp_module_coming(struct module *mod) { return 0; }

@@ -242,6 +247,15 @@ static inline bool klp_patch_pending(struct task_struct *task) { return false; }
 static inline void klp_update_patch_state(struct task_struct *task) {}
 static inline void klp_copy_process(struct task_struct *child) {}
 
+static inline
+int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
+			     const char *shstrtab, const char *strtab,
+			     unsigned int symindex, unsigned int secindex,
+			     const char *objname)
+{
+	return 0;
+}
+
 #endif /* CONFIG_LIVEPATCH */
 
 #endif /* _LINUX_LIVEPATCH_H_ */

kernel/livepatch/core.c +83 ~~-51~~

180 lines not on this page · raw message

kernel/module.c +6 -4

index d626dc31b37f..96b2575329f4 100644
@@ -2363,11 +2363,13 @@ static int apply_relocations(struct module *mod, const struct load_info *info)
 		if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
 			continue;
 
-		/* Livepatch relocation sections are applied by livepatch */
 		if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
-			continue;
-
-		if (info->sechdrs[i].sh_type == SHT_REL)
+			err = klp_apply_section_relocs(mod, info->sechdrs,
+						       info->secstrings,
+						       info->strtab,
+						       info->index.sym, i,
+						       NULL);
+		else if (info->sechdrs[i].sh_type == SHT_REL)
 			err = apply_relocate(info->sechdrs, info->strtab,
 					     info->index.sym, i, mod);
 		else if (info->sechdrs[i].sh_type == SHT_RELA)

Signature · 1 line

2.21.1

Miroslav Benes

maintainer

2020-04-28 09:20 UTC #3 lore raw

Re: [PATCH v3 02/10] livepatch: Apply vmlinux-specific KLP relocations early

Quoted 11 lines

kernel/livepatch/core.c +0 -6

@@ -738,18 +765,23 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 	int ret;
 
 	mutex_lock(&text_mutex);
-
 	module_disable_ro(patch->mod);
-	ret = klp_write_object_relocations(patch->mod, obj);
-	if (ret) {
-		module_enable_ro(patch->mod, true);
-		mutex_unlock(&text_mutex);
-		return ret;

kernel/livepatch/core.c static int klp_init_object_loaded(struct klp_patch *patch, · line 778

Quoted 10 lines

kernel/livepatch/core.c +10 -0

+
+	if (klp_is_module(obj)) {
+		/*
+		 * Only write module-specific relocations here
+		 * (.klp.rela.{module}.*).  vmlinux-specific relocations were
+		 * written earlier during the initialization of the klp module
+		 * itself.
+		 */
+		ret = klp_apply_object_relocs(patch, obj);
+		if (ret)

+ module_enable_ro(patch->mod, true);
+ mutex_unlock(&text_mutex);

is missing here, I think. Probably lost during rebase. It is fine after the next patch.

kernel/livepatch/core.c static int klp_init_object_loaded(struct klp_patch *patch, · line 785

Quoted 8 lines

kernel/livepatch/core.c +2 -1

+			return ret;
 	}
 
 	arch_klp_init_object_loaded(patch, obj);
-	module_enable_ro(patch->mod, true);
 
+	module_enable_ro(patch->mod, true);
 	mutex_unlock(&text_mutex);

Miroslav

Josh Poimboeuf

author

2020-04-25 11:09 UTC #4 lore raw

PATCH v3 3/10 livepatch: Remove .klp.arch

In reply to Josh Poimboeuf

From: Peter Zijlstra <[email protected]>

After the previous patch, vmlinux-specific KLP relocations are now applied early during KLP module load. This means that .klp.arch sections are no longer needed for *vmlinux-specific* KLP relocations.

One might think they're still needed for *module-specific* KLP relocations. If a to-be-patched module is loaded *after* its corresponding KLP module is loaded, any corresponding KLP relocations will be delayed until the to-be-patched module is loaded. If any special sections (.parainstructions, for example) rely on those relocations, their initializations (apply_paravirt) need to be done afterwards. Thus the apparent need for arch_klp_init_object_loaded() and its corresponding .klp.arch sections -- it allows some of the special section initializations to be done at a later time.

But... if you look closer, that dependency between the special sections and the module-specific KLP relocations doesn't actually exist in reality. Looking at the contents of the .altinstructions and .parainstructions sections, there's not a realistic scenario in which a KLP module's .altinstructions or .parainstructions section needs to access a symbol in a to-be-patched module. It might need to access a local symbol or even a vmlinux symbol; but not another module's symbol. When a special section needs to reference a local or vmlinux symbol, a normal rela can be used instead of a KLP rela.

Since the special section initializations don't actually have any real dependency on module-specific KLP relocations, .klp.arch and arch_klp_init_object_loaded() no longer have a reason to exist. So remove them.

As Peter said much more succinctly:

So the reason for .klp.arch was that .klp.rela.* stuff would overwrite paravirt instructions. If that happens you're doing it wrong. Those RELAs are core kernel, not module, and thus should've happened in .rela.* sections at patch-module loading time.

Reverting this removes the two apply_{paravirt,alternatives}() calls from the late patching path, and means we don't have to worry about them when removing module_disable_ro().

[ jpoimboe: Rewrote patch description. Tweaked klp_init_object_loaded()
error path. ]

Signed-off-by Peter Zijlstra (Intel) <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Peter Zijlstra (Intel) <[email protected]>

---
 Documentation/livepatch/module-elf-format.rst | 15 +-----
 arch/x86/kernel/Makefile                      |  1 -
 arch/x86/kernel/livepatch.c                   | 53 -------------------
 include/linux/livepatch.h                     |  3 --
 kernel/livepatch/core.c                       | 22 +++-----
 5 files changed, 10 insertions(+), 84 deletions(-)
 delete mode 100644 arch/x86/kernel/livepatch.c

Documentation/livepatch/module-elf-format.rst +2 ~~-13~~

index 2a591e6f8e6c..8c6b894c4661 100644
@@ -14,8 +14,7 @@ This document outlines the Elf format requirements that livepatch modules must f
    4. Livepatch symbols
       4.1 A livepatch module's symbol table
       4.2 Livepatch symbol format
-   5. Architecture-specific sections
-   6. Symbol table and Elf section access
+   5. Symbol table and Elf section access
 
 1. Background and motivation
 ============================

@@ -298,17 +297,7 @@ Examples:
   Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20).
   "OS" means OS-specific.
 
-5. Architecture-specific sections
-=================================
-Architectures may override arch_klp_init_object_loaded() to perform
-additional arch-specific tasks when a target module loads, such as applying
-arch-specific sections. On x86 for example, we must apply per-object
-.altinstructions and .parainstructions sections when a target module loads.
-These sections must be prefixed with ".klp.arch.$objname." so that they can
-be easily identified when iterating through a patch module's Elf sections
-(See arch/x86/kernel/livepatch.c for a complete example).
-
-6. Symbol table and Elf section access
+5. Symbol table and Elf section access
 ======================================
 A livepatch module's symbol table is accessible through module->symtab.

arch/x86/kernel/Makefile +0 -1

index 92e1261ec4ec..e77261db2391 100644
@@ -94,7 +94,6 @@ obj-$(CONFIG_X86_MPPARSE)	+= mpparse.o
 obj-y				+= apic/
 obj-$(CONFIG_X86_REBOOTFIXUPS)	+= reboot_fixups_32.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o
-obj-$(CONFIG_LIVEPATCH)	+= livepatch.o
 obj-$(CONFIG_FUNCTION_TRACER)	+= ftrace_$(BITS).o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o

arch/x86/kernel/livepatch.c deleted +0 ~~-53~~

53 lines not on this page · raw message

include/linux/livepatch.h +0 -3

index c4302e9a5905..2614247a9781 100644
@@ -195,9 +195,6 @@ struct klp_patch {
 
 int klp_enable_patch(struct klp_patch *);
 
-void arch_klp_init_object_loaded(struct klp_patch *patch,
-				 struct klp_object *obj);
-
 /* Called from the module loader during module coming/going states */
 int klp_module_coming(struct module *mod);
 void klp_module_going(struct module *mod);

kernel/livepatch/core.c +8 ~~-14~~

index 86a45d8a593b..16632e75112a 100644
@@ -729,12 +729,6 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 			   func->old_sympos ? func->old_sympos : 1);
 }
 
-/* Arches may override this to finish any remaining arch-specific tasks */
-void __weak arch_klp_init_object_loaded(struct klp_patch *patch,
-					struct klp_object *obj)
-{
-}
-
 int klp_apply_object_relocs(struct klp_patch *patch, struct klp_object *obj)
 {
 	int i, ret;

@@ -764,10 +758,11 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 	struct klp_func *func;
 	int ret;
 
-	mutex_lock(&text_mutex);
-	module_disable_ro(patch->mod);
-
 	if (klp_is_module(obj)) {
+
+		mutex_lock(&text_mutex);
+		module_disable_ro(patch->mod);
+
 		/*
 		 * Only write module-specific relocations here
 		 * (.klp.rela.{module}.*).  vmlinux-specific relocations were

@@ -775,15 +770,14 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 		 * itself.
 		 */
 		ret = klp_apply_object_relocs(patch, obj);
+
+		module_enable_ro(patch->mod, true);
+		mutex_unlock(&text_mutex);
+
 		if (ret)
 			return ret;
 	}
 
-	arch_klp_init_object_loaded(patch, obj);
-
-	module_enable_ro(patch->mod, true);
-	mutex_unlock(&text_mutex);
-
 	klp_for_each_func(obj, func) {
 		ret = klp_find_object_symbol(obj->name, func->old_name,
 					     func->old_sympos,

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:08 UTC #5 lore raw

PATCH v3 4/10 livepatch: Prevent module-specific KLP rela sections from referencing vmlinux symbols

In reply to Josh Poimboeuf

Prevent module-specific KLP rela sections from referencing vmlinux symbols. This helps prevent ordering issues with module special section initializations. Presumably such symbols are exported and normal relas can be used instead.

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Peter Zijlstra (Intel) <[email protected]>

---
 kernel/livepatch/core.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

kernel/livepatch/core.c +27 ~~-11~~

index 16632e75112a..f9ebb54affab 100644
@@ -192,17 +192,20 @@ static int klp_find_object_symbol(const char *objname, const char *name,
 }
 
 static int klp_resolve_symbols(Elf64_Shdr *sechdrs, const char *strtab,
-			       unsigned int symndx, Elf_Shdr *relasec)
+			       unsigned int symndx, Elf_Shdr *relasec,
+			       const char *sec_objname)
 {
-	int i, cnt, vmlinux, ret;
-	char objname[MODULE_NAME_LEN];
-	char symname[KSYM_NAME_LEN];
+	int i, cnt, ret;
+	char sym_objname[MODULE_NAME_LEN];
+	char sym_name[KSYM_NAME_LEN];
 	Elf_Rela *relas;
 	Elf_Sym *sym;
 	unsigned long sympos, addr;
+	bool sym_vmlinux;
+	bool sec_vmlinux = !strcmp(sec_objname, "vmlinux");
 
 	/*
-	 * Since the field widths for objname and symname in the sscanf()
+	 * Since the field widths for sym_objname and sym_name in the sscanf()
 	 * call are hard-coded and correspond to MODULE_NAME_LEN and
 	 * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
 	 * and KSYM_NAME_LEN have the values we expect them to have.

@@ -223,20 +226,33 @@ static int klp_resolve_symbols(Elf64_Shdr *sechdrs, const char *strtab,
 			return -EINVAL;
 		}
 
-		/* Format: .klp.sym.objname.symname,sympos */
+		/* Format: .klp.sym.sym_objname.sym_name,sympos */
 		cnt = sscanf(strtab + sym->st_name,
 			     ".klp.sym.%55[^.].%127[^,],%lu",
-			     objname, symname, &sympos);
+			     sym_objname, sym_name, &sympos);
 		if (cnt != 3) {
 			pr_err("symbol %s has an incorrectly formatted name\n",
 			       strtab + sym->st_name);
 			return -EINVAL;
 		}
 
+		sym_vmlinux = !strcmp(sym_objname, "vmlinux");
+
+		/*
+		 * Prevent module-specific KLP rela sections from referencing
+		 * vmlinux symbols.  This helps prevent ordering issues with
+		 * module special section initializations.  Presumably such
+		 * symbols are exported and normal relas can be used instead.
+		 */
+		if (!sec_vmlinux && sym_vmlinux) {
+			pr_err("invalid access to vmlinux symbol '%s' from module-specific livepatch relocation section",
+			       sym_name);
+			return -EINVAL;
+		}
+
 		/* klp_find_object_symbol() treats a NULL objname as vmlinux */
-		vmlinux = !strcmp(objname, "vmlinux");
-		ret = klp_find_object_symbol(vmlinux ? NULL : objname,
-					     symname, sympos, &addr);
+		ret = klp_find_object_symbol(sym_vmlinux ? NULL : sym_objname,
+					     sym_name, sympos, &addr);
 		if (ret)
 			return ret;

@@ -294,7 +310,7 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
 	if (strcmp(objname ? objname : "vmlinux", sec_objname))
 		return 0;
 
-	ret = klp_resolve_symbols(sechdrs, strtab, symndx, sec);
+	ret = klp_resolve_symbols(sechdrs, strtab, symndx, sec, sec_objname);
 	if (ret)
 		return ret;

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:07 UTC #6 lore raw

PATCH v3 5/10 s390: Change s390_kernel_write() return type to match memcpy()

In reply to Josh Poimboeuf

s390_kernel_write()'s function type is almost identical to memcpy(). Change its return type to "void *" so they can be used interchangeably.

Cc [email protected]

Signed-off-by Josh Poimboeuf <[email protected]>

---
 arch/s390/include/asm/uaccess.h | 2 +-
 arch/s390/mm/maccess.c          | 9 ++++++---
 2 files changed, 7 insertions(+), 4 deletions(-)

arch/s390/include/asm/uaccess.h +1 -1

index a470f1fa9f2a..324438889fe1 100644
@@ -276,6 +276,6 @@ static inline unsigned long __must_check clear_user(void __user *to, unsigned lo
 }
 
 int copy_to_user_real(void __user *dest, void *src, unsigned long count);
-void s390_kernel_write(void *dst, const void *src, size_t size);
+void *s390_kernel_write(void *dst, const void *src, size_t size);
 
 #endif /* __S390_UACCESS_H */

arch/s390/mm/maccess.c +6 -3

index de7ca4b6718f..22a0be655f27 100644
@@ -55,19 +55,22 @@ static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t siz
  */
 static DEFINE_SPINLOCK(s390_kernel_write_lock);
 
-void notrace s390_kernel_write(void *dst, const void *src, size_t size)
+notrace void *s390_kernel_write(void *dst, const void *src, size_t size)
 {
+	void *tmp = dst;
 	unsigned long flags;
 	long copied;
 
 	spin_lock_irqsave(&s390_kernel_write_lock, flags);
 	while (size) {
-		copied = s390_kernel_write_odd(dst, src, size);
-		dst += copied;
+		copied = s390_kernel_write_odd(tmp, src, size);
+		tmp += copied;
 		src += copied;
 		size -= copied;
 	}
 	spin_unlock_irqrestore(&s390_kernel_write_lock, flags);
+
+	return dst;
 }
 
 static int __no_sanitize_address __memcpy_real(void *dest, void *src, size_t count)

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:08 UTC #7 lore raw

PATCH v3 6/10 s390/module: Use s390_kernel_write() for late relocations

In reply to Josh Poimboeuf

From: Peter Zijlstra <[email protected]>

Because of late module patching, a livepatch module needs to be able to apply some of its relocations well after it has been loaded. Instead of playing games with module_{dis,en}able_ro(), use existing text poking mechanisms to apply relocations after module loading.

So far only x86, s390 and Power have HAVE_LIVEPATCH but only the first two also have STRICT_MODULE_RWX.

This will allow removal of the last module_disable_ro() usage in livepatch. The ultimate goal is to completely disallow making executable mappings writable.

[ jpoimboe: Split up patches. Use mod state to determine whether
memcpy() can be used. Test and add fixes. ]

Cc [email protected]

Cc Heiko Carstens [email protected]

Cc Gerald Schaefer <[email protected]>

Cc Christian Borntraeger <[email protected]>

Signed-off-by Peter Zijlstra (Intel) <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Peter Zijlstra (Intel) <[email protected]>

---
 arch/s390/kernel/module.c | 147 +++++++++++++++++++++++---------------
 1 file changed, 88 insertions(+), 59 deletions(-)

arch/s390/kernel/module.c +88 ~~-59~~

index ba8f19bb438b..4055f1c49814 100644
@@ -19,6 +19,7 @@
 #include <linux/kasan.h>
 #include <linux/moduleloader.h>
 #include <linux/bug.h>
+#include <linux/memory.h>
 #include <asm/alternative.h>
 #include <asm/nospec-branch.h>
 #include <asm/facility.h>

@@ -174,10 +175,12 @@ int module_frob_arch_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
 }
 
 static int apply_rela_bits(Elf_Addr loc, Elf_Addr val,
-			   int sign, int bits, int shift)
+			   int sign, int bits, int shift,
+			   void *(*write)(void *dest, const void *src, size_t len))
 {
 	unsigned long umax;
 	long min, max;
+	void *dest = (void *)loc;
 
 	if (val & ((1UL << shift) - 1))
 		return -ENOEXEC;

@@ -194,26 +197,33 @@ static int apply_rela_bits(Elf_Addr loc, Elf_Addr val,
 			return -ENOEXEC;
 	}
 
-	if (bits == 8)
-		*(unsigned char *) loc = val;
-	else if (bits == 12)
-		*(unsigned short *) loc = (val & 0xfff) |
+	if (bits == 8) {
+		unsigned char tmp = val;
+		write(dest, &tmp, 1);
+	} else if (bits == 12) {
+		unsigned short tmp = (val & 0xfff) |
 			(*(unsigned short *) loc & 0xf000);
-	else if (bits == 16)
-		*(unsigned short *) loc = val;
-	else if (bits == 20)
-		*(unsigned int *) loc = (val & 0xfff) << 16 |
-			(val & 0xff000) >> 4 |
-			(*(unsigned int *) loc & 0xf00000ff);
-	else if (bits == 32)
-		*(unsigned int *) loc = val;
-	else if (bits == 64)
-		*(unsigned long *) loc = val;
+		write(dest, &tmp, 2);
+	} else if (bits == 16) {
+		unsigned short tmp = val;
+		write(dest, &tmp, 2);
+	} else if (bits == 20) {
+		unsigned int tmp = (val & 0xfff) << 16 |
+			(val & 0xff000) >> 4 | (*(unsigned int *) loc & 0xf00000ff);
+		write(dest, &tmp, 4);
+	} else if (bits == 32) {
+		unsigned int tmp = val;
+		write(dest, &tmp, 4);
+	} else if (bits == 64) {
+		unsigned long tmp = val;
+		write(dest, &tmp, 8);
+	}
 	return 0;
 }
 
 static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
-		      const char *strtab, struct module *me)
+		      const char *strtab, struct module *me,
+		      void *(*write)(void *dest, const void *src, size_t len))
 {
 	struct mod_arch_syminfo *info;
 	Elf_Addr loc, val;

@@ -241,17 +251,17 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	case R_390_64:		/* Direct 64 bit.  */
 		val += rela->r_addend;
 		if (r_type == R_390_8)
-			rc = apply_rela_bits(loc, val, 0, 8, 0);
+			rc = apply_rela_bits(loc, val, 0, 8, 0, write);
 		else if (r_type == R_390_12)
-			rc = apply_rela_bits(loc, val, 0, 12, 0);
+			rc = apply_rela_bits(loc, val, 0, 12, 0, write);
 		else if (r_type == R_390_16)
-			rc = apply_rela_bits(loc, val, 0, 16, 0);
+			rc = apply_rela_bits(loc, val, 0, 16, 0, write);
 		else if (r_type == R_390_20)
-			rc = apply_rela_bits(loc, val, 1, 20, 0);
+			rc = apply_rela_bits(loc, val, 1, 20, 0, write);
 		else if (r_type == R_390_32)
-			rc = apply_rela_bits(loc, val, 0, 32, 0);
+			rc = apply_rela_bits(loc, val, 0, 32, 0, write);
 		else if (r_type == R_390_64)
-			rc = apply_rela_bits(loc, val, 0, 64, 0);
+			rc = apply_rela_bits(loc, val, 0, 64, 0, write);
 		break;
 	case R_390_PC16:	/* PC relative 16 bit.  */
 	case R_390_PC16DBL:	/* PC relative 16 bit shifted by 1.  */

@@ -260,15 +270,15 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	case R_390_PC64:	/* PC relative 64 bit.	*/
 		val += rela->r_addend - loc;
 		if (r_type == R_390_PC16)
-			rc = apply_rela_bits(loc, val, 1, 16, 0);
+			rc = apply_rela_bits(loc, val, 1, 16, 0, write);
 		else if (r_type == R_390_PC16DBL)
-			rc = apply_rela_bits(loc, val, 1, 16, 1);
+			rc = apply_rela_bits(loc, val, 1, 16, 1, write);
 		else if (r_type == R_390_PC32DBL)
-			rc = apply_rela_bits(loc, val, 1, 32, 1);
+			rc = apply_rela_bits(loc, val, 1, 32, 1, write);
 		else if (r_type == R_390_PC32)
-			rc = apply_rela_bits(loc, val, 1, 32, 0);
+			rc = apply_rela_bits(loc, val, 1, 32, 0, write);
 		else if (r_type == R_390_PC64)
-			rc = apply_rela_bits(loc, val, 1, 64, 0);
+			rc = apply_rela_bits(loc, val, 1, 64, 0, write);
 		break;
 	case R_390_GOT12:	/* 12 bit GOT offset.  */
 	case R_390_GOT16:	/* 16 bit GOT offset.  */

@@ -283,33 +293,33 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	case R_390_GOTPLT64:	/* 64 bit offset to jump slot.	*/
 	case R_390_GOTPLTENT:	/* 32 bit rel. offset to jump slot >> 1. */
 		if (info->got_initialized == 0) {
-			Elf_Addr *gotent;
+			Elf_Addr *gotent = me->core_layout.base +
+					   me->arch.got_offset +
+					   info->got_offset;
 
-			gotent = me->core_layout.base + me->arch.got_offset +
-				info->got_offset;
-			*gotent = val;
+			write(gotent, &val, sizeof(*gotent));
 			info->got_initialized = 1;
 		}
 		val = info->got_offset + rela->r_addend;
 		if (r_type == R_390_GOT12 ||
 		    r_type == R_390_GOTPLT12)
-			rc = apply_rela_bits(loc, val, 0, 12, 0);
+			rc = apply_rela_bits(loc, val, 0, 12, 0, write);
 		else if (r_type == R_390_GOT16 ||
 			 r_type == R_390_GOTPLT16)
-			rc = apply_rela_bits(loc, val, 0, 16, 0);
+			rc = apply_rela_bits(loc, val, 0, 16, 0, write);
 		else if (r_type == R_390_GOT20 ||
 			 r_type == R_390_GOTPLT20)
-			rc = apply_rela_bits(loc, val, 1, 20, 0);
+			rc = apply_rela_bits(loc, val, 1, 20, 0, write);
 		else if (r_type == R_390_GOT32 ||
 			 r_type == R_390_GOTPLT32)
-			rc = apply_rela_bits(loc, val, 0, 32, 0);
+			rc = apply_rela_bits(loc, val, 0, 32, 0, write);
 		else if (r_type == R_390_GOT64 ||
 			 r_type == R_390_GOTPLT64)
-			rc = apply_rela_bits(loc, val, 0, 64, 0);
+			rc = apply_rela_bits(loc, val, 0, 64, 0, write);
 		else if (r_type == R_390_GOTENT ||
 			 r_type == R_390_GOTPLTENT) {
 			val += (Elf_Addr) me->core_layout.base - loc;
-			rc = apply_rela_bits(loc, val, 1, 32, 1);
+			rc = apply_rela_bits(loc, val, 1, 32, 1, write);
 		}
 		break;
 	case R_390_PLT16DBL:	/* 16 bit PC rel. PLT shifted by 1.  */

@@ -320,25 +330,29 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	case R_390_PLTOFF32:	/* 32 bit offset from GOT to PLT. */
 	case R_390_PLTOFF64:	/* 16 bit offset from GOT to PLT. */
 		if (info->plt_initialized == 0) {
-			unsigned int *ip;
-			ip = me->core_layout.base + me->arch.plt_offset +
-				info->plt_offset;
-			ip[0] = 0x0d10e310;	/* basr 1,0  */
-			ip[1] = 0x100a0004;	/* lg	1,10(1) */
+			unsigned int insn[5];
+			unsigned int *ip = me->core_layout.base +
+					   me->arch.plt_offset +
+					   info->plt_offset;
+
+			insn[0] = 0x0d10e310;	/* basr 1,0  */
+			insn[1] = 0x100a0004;	/* lg	1,10(1) */
 			if (IS_ENABLED(CONFIG_EXPOLINE) && !nospec_disable) {
 				unsigned int *ij;
 				ij = me->core_layout.base +
 					me->arch.plt_offset +
 					me->arch.plt_size - PLT_ENTRY_SIZE;
-				ip[2] = 0xa7f40000 +	/* j __jump_r1 */
+				insn[2] = 0xa7f40000 +	/* j __jump_r1 */
 					(unsigned int)(u16)
 					(((unsigned long) ij - 8 -
 					  (unsigned long) ip) / 2);
 			} else {
-				ip[2] = 0x07f10000;	/* br %r1 */
+				insn[2] = 0x07f10000;	/* br %r1 */
 			}
-			ip[3] = (unsigned int) (val >> 32);
-			ip[4] = (unsigned int) val;
+			insn[3] = (unsigned int) (val >> 32);
+			insn[4] = (unsigned int) val;
+
+			write(ip, insn, sizeof(insn));
 			info->plt_initialized = 1;
 		}
 		if (r_type == R_390_PLTOFF16 ||

@@ -357,17 +371,17 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 			val += rela->r_addend - loc;
 		}
 		if (r_type == R_390_PLT16DBL)
-			rc = apply_rela_bits(loc, val, 1, 16, 1);
+			rc = apply_rela_bits(loc, val, 1, 16, 1, write);
 		else if (r_type == R_390_PLTOFF16)
-			rc = apply_rela_bits(loc, val, 0, 16, 0);
+			rc = apply_rela_bits(loc, val, 0, 16, 0, write);
 		else if (r_type == R_390_PLT32DBL)
-			rc = apply_rela_bits(loc, val, 1, 32, 1);
+			rc = apply_rela_bits(loc, val, 1, 32, 1, write);
 		else if (r_type == R_390_PLT32 ||
 			 r_type == R_390_PLTOFF32)
-			rc = apply_rela_bits(loc, val, 0, 32, 0);
+			rc = apply_rela_bits(loc, val, 0, 32, 0, write);
 		else if (r_type == R_390_PLT64 ||
 			 r_type == R_390_PLTOFF64)
-			rc = apply_rela_bits(loc, val, 0, 64, 0);
+			rc = apply_rela_bits(loc, val, 0, 64, 0, write);
 		break;
 	case R_390_GOTOFF16:	/* 16 bit offset to GOT.  */
 	case R_390_GOTOFF32:	/* 32 bit offset to GOT.  */

@@ -375,20 +389,20 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 		val = val + rela->r_addend -
 			((Elf_Addr) me->core_layout.base + me->arch.got_offset);
 		if (r_type == R_390_GOTOFF16)
-			rc = apply_rela_bits(loc, val, 0, 16, 0);
+			rc = apply_rela_bits(loc, val, 0, 16, 0, write);
 		else if (r_type == R_390_GOTOFF32)
-			rc = apply_rela_bits(loc, val, 0, 32, 0);
+			rc = apply_rela_bits(loc, val, 0, 32, 0, write);
 		else if (r_type == R_390_GOTOFF64)
-			rc = apply_rela_bits(loc, val, 0, 64, 0);
+			rc = apply_rela_bits(loc, val, 0, 64, 0, write);
 		break;
 	case R_390_GOTPC:	/* 32 bit PC relative offset to GOT. */
 	case R_390_GOTPCDBL:	/* 32 bit PC rel. off. to GOT shifted by 1. */
 		val = (Elf_Addr) me->core_layout.base + me->arch.got_offset +
 			rela->r_addend - loc;
 		if (r_type == R_390_GOTPC)
-			rc = apply_rela_bits(loc, val, 1, 32, 0);
+			rc = apply_rela_bits(loc, val, 1, 32, 0, write);
 		else if (r_type == R_390_GOTPCDBL)
-			rc = apply_rela_bits(loc, val, 1, 32, 1);
+			rc = apply_rela_bits(loc, val, 1, 32, 1, write);
 		break;
 	case R_390_COPY:
 	case R_390_GLOB_DAT:	/* Create GOT entry.  */

@@ -412,9 +426,10 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	return 0;
 }
 
-int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
+static int __apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 		       unsigned int symindex, unsigned int relsec,
-		       struct module *me)
+		       struct module *me,
+		       void *(*write)(void *dest, const void *src, size_t len))
 {
 	Elf_Addr base;
 	Elf_Sym *symtab;

@@ -430,13 +445,27 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 	n = sechdrs[relsec].sh_size / sizeof(Elf_Rela);
 
 	for (i = 0; i < n; i++, rela++) {
-		rc = apply_rela(rela, base, symtab, strtab, me);
+		rc = apply_rela(rela, base, symtab, strtab, me, write);
 		if (rc)
 			return rc;
 	}
 	return 0;
 }
 
+int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
+		       unsigned int symindex, unsigned int relsec,
+		       struct module *me)
+{
+	bool early = me->state == MODULE_STATE_UNFORMED;
+	void *(*write)(void *, const void *, size_t) = memcpy;
+
+	if (!early)
+		write = s390_kernel_write;
+
+	return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
+				    write);
+}
+
 int module_finalize(const Elf_Ehdr *hdr,
 		    const Elf_Shdr *sechdrs,
 		    struct module *me)

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:15 UTC #8 lore raw

Re: [PATCH v3 06/10] s390/module: Use s390_kernel_write() for late relocations

Quoted 14 lines · Josh Poimboeuf

From: Peter Zijlstra <[email protected]>
Because of late module patching, a livepatch module needs to be able to apply some of its relocations well after it has been loaded. Instead of playing games with module_{dis,en}able_ro(), use existing text poking mechanisms to apply relocations after module loading.
So far only x86, s390 and Power have HAVE_LIVEPATCH but only the first two also have STRICT_MODULE_RWX.
This will allow removal of the last module_disable_ro() usage in livepatch. The ultimate goal is to completely disallow making executable mappings writable.

Quoted 5 lines

[ jpoimboe: Split up patches. Use mod state to determine whether
memcpy() can be used. Test and add fixes. ]
Cc [email protected]
Cc Heiko Carstens [email protected]

Gah, I somehow messed up the formatting on this Cc, should be

Cc Heiko Carstens <[email protected]>

Quoted 307 lines

Cc Gerald Schaefer <[email protected]>

Cc Christian Borntraeger <[email protected]>

Signed-off-by Peter Zijlstra (Intel) <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Peter Zijlstra (Intel) <[email protected]>

---
 arch/s390/kernel/module.c | 147 +++++++++++++++++++++++---------------
 1 file changed, 88 insertions(+), 59 deletions(-)

arch/s390/kernel/module.c +88 ~~-59~~

index ba8f19bb438b..4055f1c49814 100644
@@ -19,6 +19,7 @@
 #include <linux/kasan.h>
 #include <linux/moduleloader.h>
 #include <linux/bug.h>
+#include <linux/memory.h>
 #include <asm/alternative.h>
 #include <asm/nospec-branch.h>
 #include <asm/facility.h>

@@ -174,10 +175,12 @@ int module_frob_arch_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
 }
 
 static int apply_rela_bits(Elf_Addr loc, Elf_Addr val,
-			   int sign, int bits, int shift)
+			   int sign, int bits, int shift,
+			   void *(*write)(void *dest, const void *src, size_t len))
 {
 	unsigned long umax;
 	long min, max;
+	void *dest = (void *)loc;
 
 	if (val & ((1UL << shift) - 1))
 		return -ENOEXEC;

@@ -194,26 +197,33 @@ static int apply_rela_bits(Elf_Addr loc, Elf_Addr val,
 			return -ENOEXEC;
 	}
 
-	if (bits == 8)
-		*(unsigned char *) loc = val;
-	else if (bits == 12)
-		*(unsigned short *) loc = (val & 0xfff) |
+	if (bits == 8) {
+		unsigned char tmp = val;
+		write(dest, &tmp, 1);
+	} else if (bits == 12) {
+		unsigned short tmp = (val & 0xfff) |
 			(*(unsigned short *) loc & 0xf000);
-	else if (bits == 16)
-		*(unsigned short *) loc = val;
-	else if (bits == 20)
-		*(unsigned int *) loc = (val & 0xfff) << 16 |
-			(val & 0xff000) >> 4 |
-			(*(unsigned int *) loc & 0xf00000ff);
-	else if (bits == 32)
-		*(unsigned int *) loc = val;
-	else if (bits == 64)
-		*(unsigned long *) loc = val;
+		write(dest, &tmp, 2);
+	} else if (bits == 16) {
+		unsigned short tmp = val;
+		write(dest, &tmp, 2);
+	} else if (bits == 20) {
+		unsigned int tmp = (val & 0xfff) << 16 |
+			(val & 0xff000) >> 4 | (*(unsigned int *) loc & 0xf00000ff);
+		write(dest, &tmp, 4);
+	} else if (bits == 32) {
+		unsigned int tmp = val;
+		write(dest, &tmp, 4);
+	} else if (bits == 64) {
+		unsigned long tmp = val;
+		write(dest, &tmp, 8);
+	}
 	return 0;
 }
 
 static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
-		      const char *strtab, struct module *me)
+		      const char *strtab, struct module *me,
+		      void *(*write)(void *dest, const void *src, size_t len))
 {
 	struct mod_arch_syminfo *info;
 	Elf_Addr loc, val;

@@ -241,17 +251,17 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	case R_390_64:		/* Direct 64 bit.  */
 		val += rela->r_addend;
 		if (r_type == R_390_8)
-			rc = apply_rela_bits(loc, val, 0, 8, 0);
+			rc = apply_rela_bits(loc, val, 0, 8, 0, write);
 		else if (r_type == R_390_12)
-			rc = apply_rela_bits(loc, val, 0, 12, 0);
+			rc = apply_rela_bits(loc, val, 0, 12, 0, write);
 		else if (r_type == R_390_16)
-			rc = apply_rela_bits(loc, val, 0, 16, 0);
+			rc = apply_rela_bits(loc, val, 0, 16, 0, write);
 		else if (r_type == R_390_20)
-			rc = apply_rela_bits(loc, val, 1, 20, 0);
+			rc = apply_rela_bits(loc, val, 1, 20, 0, write);
 		else if (r_type == R_390_32)
-			rc = apply_rela_bits(loc, val, 0, 32, 0);
+			rc = apply_rela_bits(loc, val, 0, 32, 0, write);
 		else if (r_type == R_390_64)
-			rc = apply_rela_bits(loc, val, 0, 64, 0);
+			rc = apply_rela_bits(loc, val, 0, 64, 0, write);
 		break;
 	case R_390_PC16:	/* PC relative 16 bit.  */
 	case R_390_PC16DBL:	/* PC relative 16 bit shifted by 1.  */

@@ -260,15 +270,15 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	case R_390_PC64:	/* PC relative 64 bit.	*/
 		val += rela->r_addend - loc;
 		if (r_type == R_390_PC16)
-			rc = apply_rela_bits(loc, val, 1, 16, 0);
+			rc = apply_rela_bits(loc, val, 1, 16, 0, write);
 		else if (r_type == R_390_PC16DBL)
-			rc = apply_rela_bits(loc, val, 1, 16, 1);
+			rc = apply_rela_bits(loc, val, 1, 16, 1, write);
 		else if (r_type == R_390_PC32DBL)
-			rc = apply_rela_bits(loc, val, 1, 32, 1);
+			rc = apply_rela_bits(loc, val, 1, 32, 1, write);
 		else if (r_type == R_390_PC32)
-			rc = apply_rela_bits(loc, val, 1, 32, 0);
+			rc = apply_rela_bits(loc, val, 1, 32, 0, write);
 		else if (r_type == R_390_PC64)
-			rc = apply_rela_bits(loc, val, 1, 64, 0);
+			rc = apply_rela_bits(loc, val, 1, 64, 0, write);
 		break;
 	case R_390_GOT12:	/* 12 bit GOT offset.  */
 	case R_390_GOT16:	/* 16 bit GOT offset.  */

@@ -283,33 +293,33 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	case R_390_GOTPLT64:	/* 64 bit offset to jump slot.	*/
 	case R_390_GOTPLTENT:	/* 32 bit rel. offset to jump slot >> 1. */
 		if (info->got_initialized == 0) {
-			Elf_Addr *gotent;
+			Elf_Addr *gotent = me->core_layout.base +
+					   me->arch.got_offset +
+					   info->got_offset;
 
-			gotent = me->core_layout.base + me->arch.got_offset +
-				info->got_offset;
-			*gotent = val;
+			write(gotent, &val, sizeof(*gotent));
 			info->got_initialized = 1;
 		}
 		val = info->got_offset + rela->r_addend;
 		if (r_type == R_390_GOT12 ||
 		    r_type == R_390_GOTPLT12)
-			rc = apply_rela_bits(loc, val, 0, 12, 0);
+			rc = apply_rela_bits(loc, val, 0, 12, 0, write);
 		else if (r_type == R_390_GOT16 ||
 			 r_type == R_390_GOTPLT16)
-			rc = apply_rela_bits(loc, val, 0, 16, 0);
+			rc = apply_rela_bits(loc, val, 0, 16, 0, write);
 		else if (r_type == R_390_GOT20 ||
 			 r_type == R_390_GOTPLT20)
-			rc = apply_rela_bits(loc, val, 1, 20, 0);
+			rc = apply_rela_bits(loc, val, 1, 20, 0, write);
 		else if (r_type == R_390_GOT32 ||
 			 r_type == R_390_GOTPLT32)
-			rc = apply_rela_bits(loc, val, 0, 32, 0);
+			rc = apply_rela_bits(loc, val, 0, 32, 0, write);
 		else if (r_type == R_390_GOT64 ||
 			 r_type == R_390_GOTPLT64)
-			rc = apply_rela_bits(loc, val, 0, 64, 0);
+			rc = apply_rela_bits(loc, val, 0, 64, 0, write);
 		else if (r_type == R_390_GOTENT ||
 			 r_type == R_390_GOTPLTENT) {
 			val += (Elf_Addr) me->core_layout.base - loc;
-			rc = apply_rela_bits(loc, val, 1, 32, 1);
+			rc = apply_rela_bits(loc, val, 1, 32, 1, write);
 		}
 		break;
 	case R_390_PLT16DBL:	/* 16 bit PC rel. PLT shifted by 1.  */

@@ -320,25 +330,29 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	case R_390_PLTOFF32:	/* 32 bit offset from GOT to PLT. */
 	case R_390_PLTOFF64:	/* 16 bit offset from GOT to PLT. */
 		if (info->plt_initialized == 0) {
-			unsigned int *ip;
-			ip = me->core_layout.base + me->arch.plt_offset +
-				info->plt_offset;
-			ip[0] = 0x0d10e310;	/* basr 1,0  */
-			ip[1] = 0x100a0004;	/* lg	1,10(1) */
+			unsigned int insn[5];
+			unsigned int *ip = me->core_layout.base +
+					   me->arch.plt_offset +
+					   info->plt_offset;
+
+			insn[0] = 0x0d10e310;	/* basr 1,0  */
+			insn[1] = 0x100a0004;	/* lg	1,10(1) */
 			if (IS_ENABLED(CONFIG_EXPOLINE) && !nospec_disable) {
 				unsigned int *ij;
 				ij = me->core_layout.base +
 					me->arch.plt_offset +
 					me->arch.plt_size - PLT_ENTRY_SIZE;
-				ip[2] = 0xa7f40000 +	/* j __jump_r1 */
+				insn[2] = 0xa7f40000 +	/* j __jump_r1 */
 					(unsigned int)(u16)
 					(((unsigned long) ij - 8 -
 					  (unsigned long) ip) / 2);
 			} else {
-				ip[2] = 0x07f10000;	/* br %r1 */
+				insn[2] = 0x07f10000;	/* br %r1 */
 			}
-			ip[3] = (unsigned int) (val >> 32);
-			ip[4] = (unsigned int) val;
+			insn[3] = (unsigned int) (val >> 32);
+			insn[4] = (unsigned int) val;
+
+			write(ip, insn, sizeof(insn));
 			info->plt_initialized = 1;
 		}
 		if (r_type == R_390_PLTOFF16 ||

@@ -357,17 +371,17 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 			val += rela->r_addend - loc;
 		}
 		if (r_type == R_390_PLT16DBL)
-			rc = apply_rela_bits(loc, val, 1, 16, 1);
+			rc = apply_rela_bits(loc, val, 1, 16, 1, write);
 		else if (r_type == R_390_PLTOFF16)
-			rc = apply_rela_bits(loc, val, 0, 16, 0);
+			rc = apply_rela_bits(loc, val, 0, 16, 0, write);
 		else if (r_type == R_390_PLT32DBL)
-			rc = apply_rela_bits(loc, val, 1, 32, 1);
+			rc = apply_rela_bits(loc, val, 1, 32, 1, write);
 		else if (r_type == R_390_PLT32 ||
 			 r_type == R_390_PLTOFF32)
-			rc = apply_rela_bits(loc, val, 0, 32, 0);
+			rc = apply_rela_bits(loc, val, 0, 32, 0, write);
 		else if (r_type == R_390_PLT64 ||
 			 r_type == R_390_PLTOFF64)
-			rc = apply_rela_bits(loc, val, 0, 64, 0);
+			rc = apply_rela_bits(loc, val, 0, 64, 0, write);
 		break;
 	case R_390_GOTOFF16:	/* 16 bit offset to GOT.  */
 	case R_390_GOTOFF32:	/* 32 bit offset to GOT.  */

@@ -375,20 +389,20 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 		val = val + rela->r_addend -
 			((Elf_Addr) me->core_layout.base + me->arch.got_offset);
 		if (r_type == R_390_GOTOFF16)
-			rc = apply_rela_bits(loc, val, 0, 16, 0);
+			rc = apply_rela_bits(loc, val, 0, 16, 0, write);
 		else if (r_type == R_390_GOTOFF32)
-			rc = apply_rela_bits(loc, val, 0, 32, 0);
+			rc = apply_rela_bits(loc, val, 0, 32, 0, write);
 		else if (r_type == R_390_GOTOFF64)
-			rc = apply_rela_bits(loc, val, 0, 64, 0);
+			rc = apply_rela_bits(loc, val, 0, 64, 0, write);
 		break;
 	case R_390_GOTPC:	/* 32 bit PC relative offset to GOT. */
 	case R_390_GOTPCDBL:	/* 32 bit PC rel. off. to GOT shifted by 1. */
 		val = (Elf_Addr) me->core_layout.base + me->arch.got_offset +
 			rela->r_addend - loc;
 		if (r_type == R_390_GOTPC)
-			rc = apply_rela_bits(loc, val, 1, 32, 0);
+			rc = apply_rela_bits(loc, val, 1, 32, 0, write);
 		else if (r_type == R_390_GOTPCDBL)
-			rc = apply_rela_bits(loc, val, 1, 32, 1);
+			rc = apply_rela_bits(loc, val, 1, 32, 1, write);
 		break;
 	case R_390_COPY:
 	case R_390_GLOB_DAT:	/* Create GOT entry.  */

@@ -412,9 +426,10 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
 	return 0;
 }
 
-int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
+static int __apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 		       unsigned int symindex, unsigned int relsec,
-		       struct module *me)
+		       struct module *me,
+		       void *(*write)(void *dest, const void *src, size_t len))
 {
 	Elf_Addr base;
 	Elf_Sym *symtab;

@@ -430,13 +445,27 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 	n = sechdrs[relsec].sh_size / sizeof(Elf_Rela);
 
 	for (i = 0; i < n; i++, rela++) {
-		rc = apply_rela(rela, base, symtab, strtab, me);
+		rc = apply_rela(rela, base, symtab, strtab, me, write);
 		if (rc)
 			return rc;
 	}
 	return 0;
 }
 
+int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
+		       unsigned int symindex, unsigned int relsec,
+		       struct module *me)
+{
+	bool early = me->state == MODULE_STATE_UNFORMED;
+	void *(*write)(void *, const void *, size_t) = memcpy;
+
+	if (!early)
+		write = s390_kernel_write;
+
+	return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
+				    write);
+}
+
 int module_finalize(const Elf_Ehdr *hdr,
 		    const Elf_Shdr *sechdrs,
 		    struct module *me)

Signature · 1 line

2.21.1

Signature · 1 line

Josh

Josh Poimboeuf

author

2020-04-25 11:09 UTC #9 lore raw

PATCH v3 7/10 x86/module: Use text_poke() for late relocations

In reply to Josh Poimboeuf

From: Peter Zijlstra <[email protected]>

So far only x86, s390 and Power have HAVE_LIVEPATCH but only the first two also have STRICT_MODULE_RWX.

This will allow removal of the last module_disable_ro() usage in livepatch. The ultimate goal is to completely disallow making executable mappings writable.

[ jpoimboe: Split up patches. Use mod state to determine whether
memcpy() can be used. Implement text_poke() for UML. ]

Cc [email protected]

Signed-off-by Peter Zijlstra (Intel) <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Peter Zijlstra (Intel) <[email protected]>

---
 arch/um/kernel/um_arch.c | 16 ++++++++++++++++
 arch/x86/kernel/module.c | 38 +++++++++++++++++++++++++++++++-------
 2 files changed, 47 insertions(+), 7 deletions(-)

arch/um/kernel/um_arch.c +16 -0

index 0f40eccbd759..375ab720e4aa 100644
@@ -362,3 +362,19 @@ void __init check_bugs(void)
 void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
 {
 }
+
+void *text_poke(void *addr, const void *opcode, size_t len)
+{
+	/*
+	 * In UML, the only reference to this function is in
+	 * apply_relocate_add(), which shouldn't ever actually call this
+	 * because UML doesn't have live patching.
+	 */
+	WARN_ON(1);
+
+	return memcpy(addr, opcode, len);
+}
+
+void text_poke_sync(void)
+{
+}

arch/x86/kernel/module.c +31 -7

index d5c72cb877b3..7614f478fd7a 100644
@@ -126,11 +126,12 @@ int apply_relocate(Elf32_Shdr *sechdrs,
 	return 0;
 }
 #else /*X86_64*/
-int apply_relocate_add(Elf64_Shdr *sechdrs,
+static int __apply_relocate_add(Elf64_Shdr *sechdrs,
 		   const char *strtab,
 		   unsigned int symindex,
 		   unsigned int relsec,
-		   struct module *me)
+		   struct module *me,
+		   void *(*write)(void *dest, const void *src, size_t len))
 {
 	unsigned int i;
 	Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;

@@ -162,19 +163,19 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 		case R_X86_64_64:
 			if (*(u64 *)loc != 0)
 				goto invalid_relocation;
-			*(u64 *)loc = val;
+			write(loc, &val, 8);
 			break;
 		case R_X86_64_32:
 			if (*(u32 *)loc != 0)
 				goto invalid_relocation;
-			*(u32 *)loc = val;
+			write(loc, &val, 4);
 			if (val != *(u32 *)loc)
 				goto overflow;
 			break;
 		case R_X86_64_32S:
 			if (*(s32 *)loc != 0)
 				goto invalid_relocation;
-			*(s32 *)loc = val;
+			write(loc, &val, 4);
 			if ((s64)val != *(s32 *)loc)
 				goto overflow;
 			break;

@@ -183,7 +184,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 			if (*(u32 *)loc != 0)
 				goto invalid_relocation;
 			val -= (u64)loc;
-			*(u32 *)loc = val;
+			write(loc, &val, 4);
 #if 0
 			if ((s64)val != *(s32 *)loc)
 				goto overflow;

@@ -193,7 +194,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 			if (*(u64 *)loc != 0)
 				goto invalid_relocation;
 			val -= (u64)loc;
-			*(u64 *)loc = val;
+			write(loc, &val, 8);
 			break;
 		default:
 			pr_err("%s: Unknown rela relocation: %llu\n",

@@ -215,6 +216,29 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 	       me->name);
 	return -ENOEXEC;
 }
+
+int apply_relocate_add(Elf64_Shdr *sechdrs,
+		   const char *strtab,
+		   unsigned int symindex,
+		   unsigned int relsec,
+		   struct module *me)
+{
+	int ret;
+	bool early = me->state == MODULE_STATE_UNFORMED;
+	void *(*write)(void *, const void *, size_t) = memcpy;
+
+	if (!early)
+		write = text_poke;
+
+	ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
+				   write);
+
+	if (!early)
+		text_poke_sync();
+
+	return ret;
+}
+
 #endif
 
 int module_finalize(const Elf_Ehdr *hdr,

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:08 UTC #10 lore raw

PATCH v3 8/10 livepatch: Remove module_disable_ro() usage

In reply to Josh Poimboeuf

With arch_klp_init_object_loaded() gone, and apply_relocate_add() now using text_poke(), livepatch no longer needs to use module_disable_ro().

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Peter Zijlstra (Intel) <[email protected]>

---
 kernel/livepatch/core.c | 2 --
 1 file changed, 2 deletions(-)

kernel/livepatch/core.c +0 -2

index f9ebb54affab..6b8b3c067be0 100644
@@ -777,7 +777,6 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 	if (klp_is_module(obj)) {
 
 		mutex_lock(&text_mutex);
-		module_disable_ro(patch->mod);
 
 		/*
 		 * Only write module-specific relocations here

@@ -787,7 +786,6 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 		 */
 		ret = klp_apply_object_relocs(patch, obj);
 
-		module_enable_ro(patch->mod, true);
 		mutex_unlock(&text_mutex);
 
 		if (ret)

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:09 UTC #11 lore raw

PATCH v3 9/10 module: Remove module_disable_ro()

In reply to Josh Poimboeuf

module_disable_ro() has no more users. Remove it.

Signed-off-by Josh Poimboeuf <[email protected]>

Acked-by Peter Zijlstra (Intel) <[email protected]>

---
 include/linux/module.h |  2 --
 kernel/module.c        | 13 -------------
 2 files changed, 15 deletions(-)

include/linux/module.h +0 -2

index 1ad393e62bef..e4ef7b36feda 100644
@@ -860,10 +860,8 @@ extern int module_sysfs_initialized;
 
 #ifdef CONFIG_STRICT_MODULE_RWX
 extern void module_enable_ro(const struct module *mod, bool after_init);
-extern void module_disable_ro(const struct module *mod);
 #else
 static inline void module_enable_ro(const struct module *mod, bool after_init) { }
-static inline void module_disable_ro(const struct module *mod) { }
 #endif
 
 #ifdef CONFIG_GENERIC_BUG

kernel/module.c +0 ~~-13~~

index 96b2575329f4..f0e414a01d91 100644
@@ -2016,19 +2016,6 @@ static void frob_writable_data(const struct module_layout *layout,
 		   (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
 }
 
-/* livepatching wants to disable read-only so it can frob module. */
-void module_disable_ro(const struct module *mod)
-{
-	if (!rodata_enabled)
-		return;
-
-	frob_text(&mod->core_layout, set_memory_rw);
-	frob_rodata(&mod->core_layout, set_memory_rw);
-	frob_ro_after_init(&mod->core_layout, set_memory_rw);
-	frob_text(&mod->init_layout, set_memory_rw);
-	frob_rodata(&mod->init_layout, set_memory_rw);
-}
-
 void module_enable_ro(const struct module *mod, bool after_init)
 {
 	if (!rodata_enabled)

Signature · 1 line

2.21.1

Jessica Yu

2020-04-28 16:25 UTC #12 lore raw

Re: [PATCH v3 09/10] module: Remove module_disable_ro()

+++ Josh Poimboeuf [25/04/20 06:07 -0500]:

Quoted 4 lines

module_disable_ro() has no more users. Remove it.
Signed-off-by Josh Poimboeuf <[email protected]>
Acked-by Peter Zijlstra (Intel) <[email protected]>

Hm, I guess this means we can also remove the module_enable_ro() stubs in module.h and make it a static function again (like the other module_enable_* functions) as there are no more outside users. I have to remind myself after this patchset is merged :-)

Jessica

Josh Poimboeuf

author

2020-04-28 16:36 UTC #13 lore raw

Re: [PATCH v3 09/10] module: Remove module_disable_ro()

Quoted 10 lines · Jessica Yu

+++ Josh Poimboeuf [25/04/20 06:07 -0500]:
Quoted 4 lines
module_disable_ro() has no more users. Remove it.
Signed-off-by Josh Poimboeuf <[email protected]>
Acked-by Peter Zijlstra (Intel) <[email protected]>
Hm, I guess this means we can also remove the module_enable_ro() stubs in module.h and make it a static function again (like the other module_enable_* functions) as there are no more outside users. I have to remind myself after this patchset is merged :-)

Ah, true. I'm respinning the patch set anyway, I can just add this as a another patch.

Signature · 1 line

Josh

Jessica Yu

2020-04-28 16:42 UTC #14 lore raw

Re: [PATCH v3 09/10] module: Remove module_disable_ro()

+++ Josh Poimboeuf [28/04/20 11:36 -0500]:

Quoted 7 lines · Jessica Yu

Quoted 6 lines
+++ Josh Poimboeuf [25/04/20 06:07 -0500]:
Quoted 4 lines
module_disable_ro() has no more users. Remove it.
Signed-off-by Josh Poimboeuf <[email protected]>
Acked-by Peter Zijlstra (Intel) <[email protected]>

Quoted 7 lines

Quoted 4 lines
Hm, I guess this means we can also remove the module_enable_ro() stubs in module.h and make it a static function again (like the other module_enable_* functions) as there are no more outside users. I have to remind myself after this patchset is merged :-)
Ah, true. I'm respinning the patch set anyway, I can just add this as a another patch.

That would be great. Thanks!

Josh Poimboeuf

author

2020-04-28 17:03 UTC #15 lore raw

Re: [PATCH v3 09/10] module: Remove module_disable_ro()

Quoted 13 lines · Jessica Yu

+++ Josh Poimboeuf [28/04/20 11:36 -0500]:
Quoted 12 lines · Jessica Yu
Quoted 10 lines
+++ Josh Poimboeuf [25/04/20 06:07 -0500]:
Quoted 4 lines
module_disable_ro() has no more users. Remove it.
Signed-off-by Josh Poimboeuf <[email protected]>
Acked-by Peter Zijlstra (Intel) <[email protected]>
Hm, I guess this means we can also remove the module_enable_ro() stubs in module.h and make it a static function again (like the other module_enable_* functions) as there are no more outside users. I have to remind myself after this patchset is merged :-)

Quoted 4 lines

Quoted 2 lines
Ah, true. I'm respinning the patch set anyway, I can just add this as a another patch.
That would be great. Thanks!

Sneak preview:

From: Josh Poimboeuf <[email protected]>
Subject: [PATCH] module: Make module_enable_ro() static again

Now that module_enable_ro() has no more external users, make it static again.

Signed-off-by Josh Poimboeuf <[email protected]>

---
 include/linux/module.h | 6 ------
 kernel/module.c        | 4 ++--
 2 files changed, 2 insertions(+), 8 deletions(-)

include/linux/module.h +0 -6

index e4ef7b36feda..2c2e988bcf10 100644
@@ -858,12 +858,6 @@ extern int module_sysfs_initialized;
 
 #define __MODULE_STRING(x) __stringify(x)
 
-#ifdef CONFIG_STRICT_MODULE_RWX
-extern void module_enable_ro(const struct module *mod, bool after_init);
-#else
-static inline void module_enable_ro(const struct module *mod, bool after_init) { }
-#endif
-
 #ifdef CONFIG_GENERIC_BUG
 void module_bug_finalize(const Elf_Ehdr *, const Elf_Shdr *,
 			 struct module *);

kernel/module.c +2 -2

index f0e414a01d91..6d8aab60943e 100644
@@ -2016,7 +2016,7 @@ static void frob_writable_data(const struct module_layout *layout,
 		   (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
 }
 
-void module_enable_ro(const struct module *mod, bool after_init)
+static void module_enable_ro(const struct module *mod, bool after_init)
 {
 	if (!rodata_enabled)
 		return;

@@ -2057,7 +2057,7 @@ static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
 }
 
 #else /* !CONFIG_STRICT_MODULE_RWX */
-/* module_{enable,disable}_ro() stubs are in module.h */
+void module_enable_ro(const struct module *mod, bool after_init) {}
 static void module_enable_nx(const struct module *mod) { }
 static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
 				       char *secstrings, struct module *mod)

Signature · 1 line

2.21.1

Jessica Yu

2020-04-28 18:56 UTC #16 lore raw

Re: [PATCH v3 09/10] module: Remove module_disable_ro()

+++ Josh Poimboeuf [28/04/20 12:03 -0500]:

Quoted 65 lines · Jessica Yu

Quoted 13 lines
+++ Josh Poimboeuf [28/04/20 11:36 -0500]:
Quoted 12 lines · Jessica Yu
Quoted 10 lines
+++ Josh Poimboeuf [25/04/20 06:07 -0500]:
Quoted 4 lines
module_disable_ro() has no more users. Remove it.
Signed-off-by Josh Poimboeuf <[email protected]>
Acked-by Peter Zijlstra (Intel) <[email protected]>
Hm, I guess this means we can also remove the module_enable_ro() stubs in module.h and make it a static function again (like the other module_enable_* functions) as there are no more outside users. I have to remind myself after this patchset is merged :-)
Quoted 4 lines
Quoted 2 lines
Ah, true. I'm respinning the patch set anyway, I can just add this as a another patch.
That would be great. Thanks!
Sneak preview:
From: Josh Poimboeuf <[email protected]>
Subject: [PATCH] module: Make module_enable_ro() static again
Now that module_enable_ro() has no more external users, make it static again.
Suggested-by Jessica Yu <[email protected]>
Signed-off-by Josh Poimboeuf <[email protected]>
---
include/linux/module.h | 6 ------
kernel/module.c | 4 ++--
2 files changed, 2 insertions(+), 8 deletions(-)
include/linux/module.h +0 -6
index e4ef7b36feda..2c2e988bcf10 100644
@@ -858,12 +858,6 @@ extern int module_sysfs_initialized;
 
 #define __MODULE_STRING(x) __stringify(x)
 
-#ifdef CONFIG_STRICT_MODULE_RWX
-extern void module_enable_ro(const struct module *mod, bool after_init);
-#else
-static inline void module_enable_ro(const struct module *mod, bool after_init) { }
-#endif
-
 #ifdef CONFIG_GENERIC_BUG
 void module_bug_finalize(const Elf_Ehdr *, const Elf_Shdr *,
 			 struct module *);
kernel/module.c +1 -1
index f0e414a01d91..6d8aab60943e 100644
@@ -2016,7 +2016,7 @@ static void frob_writable_data(const struct module_layout *layout,
 		   (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
 }
 
-void module_enable_ro(const struct module *mod, bool after_init)
+static void module_enable_ro(const struct module *mod, bool after_init)
 {
 	if (!rodata_enabled)
 		return;

kernel/module.c static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs, · line 2060

Quoted 5 lines

kernel/module.c +1 -1

@@ -2057,7 +2057,7 @@ static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
 }
 
 #else /* !CONFIG_STRICT_MODULE_RWX */
-/* module_{enable,disable}_ro() stubs are in module.h */
+void module_enable_ro(const struct module *mod, bool after_init) {}

Missing static here, but otherwise looks good. Thanks!

Quoted 6 lines

kernel/module.c +0 -0

 static void module_enable_nx(const struct module *mod) { }
 static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
 				       char *secstrings, struct module *mod)

Signature · 1 line

2.21.1

Josh Poimboeuf

author

2020-04-25 11:09 UTC #17 lore raw

PATCH v3 10/10 x86/module: Use text_mutex in apply_relocate_add()

In reply to Josh Poimboeuf

Now that the livepatch code no longer needs the text_mutex for changing module permissions, move its usage down to apply_relocate_add().

Note the s390 version of apply_relocate_add() doesn't need to use the text_mutex because it already uses s390_kernel_write_lock, which accomplishes the same task.

Signed-off-by Josh Poimboeuf <[email protected]>

---
 arch/x86/kernel/module.c | 9 +++++++--
 kernel/livepatch/core.c  | 6 ------
 2 files changed, 7 insertions(+), 8 deletions(-)

arch/x86/kernel/module.c +7 -2

index 7614f478fd7a..23c95a53d20e 100644
@@ -18,6 +18,7 @@
 #include <linux/gfp.h>
 #include <linux/jump_label.h>
 #include <linux/random.h>
+#include <linux/memory.h>
 
 #include <asm/text-patching.h>
 #include <asm/page.h>

@@ -227,14 +228,18 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 	bool early = me->state == MODULE_STATE_UNFORMED;
 	void *(*write)(void *, const void *, size_t) = memcpy;
 
-	if (!early)
+	if (!early) {
 		write = text_poke;
+		mutex_lock(&text_mutex);
+	}
 
 	ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
 				   write);
 
-	if (!early)
+	if (!early) {
 		text_poke_sync();
+		mutex_unlock(&text_mutex);
+	}
 
 	return ret;
 }

kernel/livepatch/core.c +0 -6

index 6b8b3c067be0..96d2da14eb0d 100644
@@ -775,9 +775,6 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 	int ret;
 
 	if (klp_is_module(obj)) {
-
-		mutex_lock(&text_mutex);
-
 		/*
 		 * Only write module-specific relocations here
 		 * (.klp.rela.{module}.*).  vmlinux-specific relocations were

@@ -785,9 +782,6 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 		 * itself.
 		 */
 		ret = klp_apply_object_relocs(patch, obj);
-
-		mutex_unlock(&text_mutex);
-
 		if (ret)
 			return ret;
 	}

Signature · 1 line

2.21.1

Joe Lawrence

maintainer

2020-04-27 12:22 UTC #18 lore raw

In reply to Josh Poimboeuf

Quoted 29 lines · Josh Poimboeuf

v3:
- klp: split klp_write_relocations() into object/section specific functions [joe]
- s390: fix plt/got writes [joe]
- s390: remove text_mutex usage [mbenes]
- x86: do text_poke_sync() before releasing text_mutex [peterz]
- split x86 text_mutex changes into separate patch [mbenes]
v2:
- add vmlinux.ko check [peterz]
- remove 'klp_object' forward declaration [mbenes]
- use text_mutex [jeyu]
- fix documentation TOC [jeyu]
- fix s390 issues [mbenes]
- upstream kpatch-build now supports this (though it's only enabled for Linux >= 5.8)
These patches add simplifications and improvements for some issues Peter found six months ago, as part of his non-writable text code (W^X) cleanups.
Highlights:
- Remove the livepatch arch-specific .klp.arch sections, which were used to do paravirt patching and alternatives patching for livepatch replacement code.
- Add support for jump labels in patched code.

Quoted 9 lines

- Remove the last module_disable_ro() usage.
For more background, see this thread:
   https://lkml.kernel.org/r/20191021135312.jbbxsuipxldocdjk@treble
This has been tested with kpatch-build integration tests and klp-convert selftests.

Hi Josh,

I've added some late module patching tests for klp-convert as well as extended the existing ones. I'll put them on-top of v3 and give it some test runs today (x86, ppc64le, s390x) and report back.

BTW, this may be out of scope for this patchset, but is it a large amount of work to support clearing klp-relocations on target module unload? ie, this test case:

- (target module and livepatch loaded)
- rmmod target_mod
- modprobe target_mod << fails as reloc target is non-zero

IIRC, Miroslav had taken a stab at this last year, but I don't remember what the technical problems were then.

-- Joe

Miroslav Benes

maintainer

2020-04-27 12:32 UTC #19 lore raw

Quoted 10 lines

BTW, this may be out of scope for this patchset, but is it a large amount of work to support clearing klp-relocations on target module unload? ie, this test case:
- (target module and livepatch loaded)
- rmmod target_mod
- modprobe target_mod << fails as reloc target is non-zero
IIRC, Miroslav had taken a stab at this last year, but I don't remember what the technical problems were then.

Yes, see
https://lore.kernel.org/live-patching/[email protected]/

I think the "conclusion" there still applies... but yes, it makes testing difficult.

Miroslav

Joe Lawrence

maintainer Acked-by

2020-04-27 16:52 UTC #20 lore raw

In reply to Joe Lawrence

Quoted 22 lines · Joe Lawrence

Quoted 21 lines · Josh Poimboeuf
v3:
- klp: split klp_write_relocations() into object/section specific functions [joe]
- s390: fix plt/got writes [joe]
- s390: remove text_mutex usage [mbenes]
- x86: do text_poke_sync() before releasing text_mutex [peterz]
- split x86 text_mutex changes into separate patch [mbenes]
v2:
- add vmlinux.ko check [peterz]
- remove 'klp_object' forward declaration [mbenes]
- use text_mutex [jeyu]
- fix documentation TOC [jeyu]
- fix s390 issues [mbenes]
- upstream kpatch-build now supports this (though it's only enabled for Linux >= 5.8)
These patches add simplifications and improvements for some issues Peter found six months ago, as part of his non-writable text code (W^X) cleanups.

Quoted 7 lines

Quoted 7 lines
Highlights:
- Remove the livepatch arch-specific .klp.arch sections, which were used to do paravirt patching and alternatives patching for livepatch replacement code.
- Add support for jump labels in patched code.

Nit: support for the hopefully common cases anyway: jump labels whose keys are not going to require late-module klp-relocation (defined in an unloaded module).

Quoted 11 lines

Quoted 10 lines
- Remove the last module_disable_ro() usage.
For more background, see this thread:
   https://lkml.kernel.org/r/20191021135312.jbbxsuipxldocdjk@treble
This has been tested with kpatch-build integration tests and klp-convert selftests.

Quoted 5 lines

Hi Josh,
I've added some late module patching tests for klp-convert as well as extended the existing ones. I'll put them on-top of v3 and give it some test runs today (x86, ppc64le, s390x) and report back.

Ok all three arches look good with the klp-convert WIP tests. For reference, I pushed the combined branch up to github [1] if anyone else wants to see the klp-relocations in action first hand.

For the series:

Acked-by Joe Lawrence <[email protected]>

[1] https://github.com/joe-lawrence/linux/tree/jp-v3-klp-convert

-- Joe

Miroslav Benes

maintainer Acked-by on the v3 series

2020-04-28 13:49 UTC #21 lore raw

In reply to Josh Poimboeuf

Quoted 53 lines · Josh Poimboeuf

v3:
- klp: split klp_write_relocations() into object/section specific functions [joe]
- s390: fix plt/got writes [joe]
- s390: remove text_mutex usage [mbenes]
- x86: do text_poke_sync() before releasing text_mutex [peterz]
- split x86 text_mutex changes into separate patch [mbenes]
v2:
- add vmlinux.ko check [peterz]
- remove 'klp_object' forward declaration [mbenes]
- use text_mutex [jeyu]
- fix documentation TOC [jeyu]
- fix s390 issues [mbenes]
- upstream kpatch-build now supports this (though it's only enabled for Linux >= 5.8)
These patches add simplifications and improvements for some issues Peter found six months ago, as part of his non-writable text code (W^X) cleanups.
Highlights:
- Remove the livepatch arch-specific .klp.arch sections, which were used to do paravirt patching and alternatives patching for livepatch replacement code.
- Add support for jump labels in patched code.
- Remove the last module_disable_ro() usage.
For more background, see this thread:
https://lkml.kernel.org/r/20191021135312.jbbxsuipxldocdjk@treble
This has been tested with kpatch-build integration tests and klp-convert selftests.
Josh Poimboeuf (7):
livepatch: Disallow vmlinux.ko
livepatch: Apply vmlinux-specific KLP relocations early
livepatch: Prevent module-specific KLP rela sections from referencing
vmlinux symbols
s390: Change s390_kernel_write() return type to match memcpy()
livepatch: Remove module_disable_ro() usage
module: Remove module_disable_ro()
x86/module: Use text_mutex in apply_relocate_add()
Peter Zijlstra (3):
livepatch: Remove .klp.arch
s390/module: Use s390_kernel_write() for late relocations x86/module: Use text_poke() for late relocations

Quoted 14 lines

 Documentation/livepatch/module-elf-format.rst |  15 +-
 arch/s390/include/asm/uaccess.h               |   2 +-
 arch/s390/kernel/module.c                     | 147 +++++++++------
 arch/s390/mm/maccess.c                        |   9 +-
 arch/um/kernel/um_arch.c                      |  16 ++
 arch/x86/kernel/Makefile                      |   1 -
 arch/x86/kernel/livepatch.c                   |  53 ------
 arch/x86/kernel/module.c                      |  43 ++++-
 include/linux/livepatch.h                     |  17 +-
 include/linux/module.h                        |   2 -
 kernel/livepatch/core.c                       | 177 +++++++++++-------
 kernel/module.c                               |  23 +--
 12 files changed, 277 insertions(+), 228 deletions(-)
 delete mode 100644 arch/x86/kernel/livepatch.c

With the small issue in patch 2 fixed

Acked-by Miroslav Benes <[email protected]>

Great stuff. I am happy we will get rid of the arch-specific code.

Josh Poimboeuf

author

2020-04-28 14:35 UTC #22 lore raw

Quoted 6 lines · Miroslav Benes

With the small issue in patch 2 fixed
Acked-by Miroslav Benes <[email protected]>
Great stuff. I am happy we will get rid of the arch-specific code.

Thanks! Good catch with the bad rebase. I'll fix it up with another revision.

Signature · 1 line

Josh