ptrace: introduce PTRACE_SET_SYSCALL_INFO API

PATCH Superseded Dmitry V. Levin 2 participants 10 messages Feb 10, 2025 – Feb 11, 2025

Subsystems (24)

Arm (32-bit) x86 PowerPC Kselftest +20 more subsystems

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Dmitry V. Levin

author

2025-02-10 11:33 UTC #0 lore raw

v5 cover ptrace: introduce PTRACE_SET_SYSCALL_INFO API

PTRACE_SET_SYSCALL_INFO is a generic ptrace API that complements PTRACE_GET_SYSCALL_INFO by letting the ptracer modify details of system calls the tracee is blocked in.

This API allows ptracers to obtain and modify system call details in a straightforward and architecture-agnostic way, providing a consistent way of manipulating the system call number and arguments across architectures.

As in case of PTRACE_GET_SYSCALL_INFO, PTRACE_SET_SYSCALL_INFO also does not aim to address numerous architecture-specific system call ABI peculiarities, like differences in the number of system call arguments for such system calls as pread64 and preadv.

The current implementation supports changing only those bits of system call information that are used by strace system call tampering, namely, syscall number, syscall arguments, and syscall return value.

Support of changing additional details returned by PTRACE_GET_SYSCALL_INFO, such as instruction pointer and stack pointer, could be added later if needed, by using struct ptrace_syscall_info.flags to specify the additional details that should be set. Currently, "flags" and "reserved" fields of struct ptrace_syscall_info must be initialized with zeroes; "arch", "instruction_pointer", and "stack_pointer" fields are currently ignored.

PTRACE_SET_SYSCALL_INFO currently supports only PTRACE_SYSCALL_INFO_ENTRY, PTRACE_SYSCALL_INFO_EXIT, and PTRACE_SYSCALL_INFO_SECCOMP operations. Other operations could be added later if needed.

Ideally, PTRACE_SET_SYSCALL_INFO should have been introduced along with PTRACE_GET_SYSCALL_INFO, but it didn't happen. The last straw that convinced me to implement PTRACE_SET_SYSCALL_INFO was apparent failure to provide an API of changing the first system call argument on riscv architecture [1].

ptrace(2) man page:

long ptrace(enum __ptrace_request request, pid_t pid, void *addr, void *data);
...
PTRACE_SET_SYSCALL_INFO
Modify information about the system call that caused the stop. The "data" argument is a pointer to struct ptrace_syscall_info that specifies the system call information to be set.
The "addr" argument should be set to sizeof(struct ptrace_syscall_info)).

[1] https://lore.kernel.org/all/[email protected]/

Notes:
v5:
* ptrace: Extend the commit message to say that the new API does not aim to address numerous architecture-specific syscall ABI peculiarities
* selftests: Add a workaround for s390 16-bit syscall numbers
* Add more Acked-by
* v4: https://lore.kernel.org/all/[email protected]/

v4:
* Split out syscall_set_return_value() for hexagon into a separate patch
* s390: Change the style of syscall_set_arguments() implementation as requested
* Add more Reviewed-by
* v3: https://lore.kernel.org/all/[email protected]/

v3:
* powerpc: Submit syscall_set_return_value() fix for "sc" case separately
* mips: Do not introduce erroneous argument truncation on mips n32, add a detailed description to the commit message of the mips_get_syscall_arg() change
* ptrace: Add explicit padding to the end of struct ptrace_syscall_info, simplify obtaining of user ptrace_syscall_info,
do not introduce PTRACE_SYSCALL_INFO_SIZE_VER0
* ptrace: Change the return type of ptrace_set_syscall_info_* functions from "unsigned long" to "int"
* ptrace: Add -ERANGE check to ptrace_set_syscall_info_exit(), add comments to -ERANGE checks
* ptrace: Update comments about supported syscall stops
* selftests: Extend set_syscall_info test, fix for mips n32
* Add Tested-by and Reviewed-by

v2:
* Add patch to fix syscall_set_return_value() on powerpc
* Add patch to fix mips_get_syscall_arg() on mips
* Add syscall_set_return_value() implementation on hexagon
* Add syscall_set_return_value() invocation to syscall_set_nr() on arm and arm64.
* Fix syscall_set_nr() and mips_set_syscall_arg() on mips
* Add a comment to syscall_set_nr() on arc, powerpc, s390, sh, and sparc
* Remove redundant ptrace_syscall_info.op assignments in ptrace_get_syscall_info_*
* Minor style tweaks in ptrace_get_syscall_info_op()
* Remove syscall_set_return_value() invocation from ptrace_set_syscall_info_entry()
* Skip syscall_set_arguments() invocation in case of syscall number -1 in ptrace_set_syscall_info_entry()
* Split ptrace_syscall_info.reserved into ptrace_syscall_info.reserved and ptrace_syscall_info.flags
* Use __kernel_ulong_t instead of unsigned long in set_syscall_info test

Dmitry V. Levin (7):
mips: fix mips_get_syscall_arg() for o32
hexagon: add syscall_set_return_value()
syscall.h: add syscall_set_arguments()
syscall.h: introduce syscall_set_nr()
ptrace_get_syscall_info: factor out ptrace_get_syscall_info_op
ptrace: introduce PTRACE_SET_SYSCALL_INFO request selftests/ptrace: add a test case for PTRACE_SET_SYSCALL_INFO

 arch/arc/include/asm/syscall.h                |  25 +
 arch/arm/include/asm/syscall.h                |  37 ++
 arch/arm64/include/asm/syscall.h              |  29 +
 arch/csky/include/asm/syscall.h               |  13 +
 arch/hexagon/include/asm/syscall.h            |  21 +
 arch/loongarch/include/asm/syscall.h          |  15 +
 arch/m68k/include/asm/syscall.h               |   7 +
 arch/microblaze/include/asm/syscall.h         |   7 +
 arch/mips/include/asm/syscall.h               |  70 ++-
 arch/nios2/include/asm/syscall.h              |  16 +
 arch/openrisc/include/asm/syscall.h           |  13 +
 arch/parisc/include/asm/syscall.h             |  19 +
 arch/powerpc/include/asm/syscall.h            |  20 +
 arch/riscv/include/asm/syscall.h              |  16 +
 arch/s390/include/asm/syscall.h               |  21 +
 arch/sh/include/asm/syscall_32.h              |  24 +
 arch/sparc/include/asm/syscall.h              |  22 +
 arch/um/include/asm/syscall-generic.h         |  19 +
 arch/x86/include/asm/syscall.h                |  43 ++
 arch/xtensa/include/asm/syscall.h             |  18 +
 include/asm-generic/syscall.h                 |  30 +
 include/uapi/linux/ptrace.h                   |   7 +-
 kernel/ptrace.c                               | 179 +++++-
 tools/testing/selftests/ptrace/Makefile       |   2 +-
 .../selftests/ptrace/set_syscall_info.c       | 519 ++++++++++++++++++
 25 files changed, 1145 insertions(+), 47 deletions(-)
 create mode 100644 tools/testing/selftests/ptrace/set_syscall_info.c

Signature · 1 line

ldv

Dmitry V. Levin

author

2025-02-10 11:34 UTC #1 lore raw

PATCH v5 1/7 mips: fix mips_get_syscall_arg() for o32

This makes ptrace/get_syscall_info selftest pass on mips o32 and mips64 o32 by fixing the following two test assertions:

1. get_syscall_info test assertion on mips o32:
# get_syscall_info.c:218:get_syscall_info:Expected exp_args[5] (3134521044) == info.entry.args[4] (4911432) # get_syscall_info.c:219:get_syscall_info:wait #1: entry stop mismatch

2. get_syscall_info test assertion on mips64 o32:
# get_syscall_info.c:209:get_syscall_info:Expected exp_args[2] (3134324433) == info.entry.args[1] (18446744072548908753) # get_syscall_info.c:210:get_syscall_info:wait #1: entry stop mismatch

The first assertion is fixed for mips o32 by using struct pt_regs.pad0 instead of get_user() to obtain syscall arguments. This approach works due to this piece in arch/mips/kernel/scall32-o32.S:

        /*
         * Ok, copy the args from the luser stack to the kernel stack.
         */

        .set    push
        .set    noreorder
        .set    nomacro

    load_a4: user_lw(t5, 16(t0))		# argument #5 from usp
    load_a5: user_lw(t6, 20(t0))		# argument #6 from usp
    load_a6: user_lw(t7, 24(t0))		# argument #7 from usp
    load_a7: user_lw(t8, 28(t0))		# argument #8 from usp
    loads_done:

        sw	t5, 16(sp)		# argument #5 to ksp
        sw	t6, 20(sp)		# argument #6 to ksp
        sw	t7, 24(sp)		# argument #7 to ksp
        sw	t8, 28(sp)		# argument #8 to ksp
        .set	pop

        .section __ex_table,"a"
        PTR_WD	load_a4, bad_stack_a4
        PTR_WD	load_a5, bad_stack_a5
        PTR_WD	load_a6, bad_stack_a6
        PTR_WD	load_a7, bad_stack_a7
        .previous

arch/mips/kernel/scall64-o32.S has analogous code for mips64 o32 that allows obtaining syscall arguments from struct pt_regs.regs[4..11] instead of get_user().

The second assertion is fixed by truncating 64-bit values to 32-bit syscall arguments.

Signed-off-by Dmitry V. Levin <[email protected]>

---
 arch/mips/include/asm/syscall.h | 32 ++++++++------------------------
 1 file changed, 8 insertions(+), 24 deletions(-)

arch/mips/include/asm/syscall.h +8 ~~-24~~

index ebdf4d910af2..b3f00ede8bb3 100644
@@ -57,37 +57,21 @@ static inline void mips_syscall_update_nr(struct task_struct *task,
 static inline void mips_get_syscall_arg(unsigned long *arg,
 	struct task_struct *task, struct pt_regs *regs, unsigned int n)
 {
-	unsigned long usp __maybe_unused = regs->regs[29];
-
+#ifdef CONFIG_32BIT
 	switch (n) {
 	case 0: case 1: case 2: case 3:
 		*arg = regs->regs[4 + n];
-
-		return;
-
-#ifdef CONFIG_32BIT
-	case 4: case 5: case 6: case 7:
-		get_user(*arg, (int *)usp + n);
 		return;
-#endif
-
-#ifdef CONFIG_64BIT
 	case 4: case 5: case 6: case 7:
-#ifdef CONFIG_MIPS32_O32
-		if (test_tsk_thread_flag(task, TIF_32BIT_REGS))
-			get_user(*arg, (int *)usp + n);
-		else
-#endif
-			*arg = regs->regs[4 + n];
-
+		*arg = regs->pad0[n];
 		return;
-#endif
-
-	default:
-		BUG();
 	}
-
-	unreachable();
+#else
+	*arg = regs->regs[4 + n];
+	if ((IS_ENABLED(CONFIG_MIPS32_O32) &&
+	     test_tsk_thread_flag(task, TIF_32BIT_REGS)))
+		*arg = (unsigned int)*arg;
+#endif
 }
 
 static inline long syscall_get_error(struct task_struct *task,

Signature · 1 line

ldv

Maciej W. Rozycki

2025-02-11 18:30 UTC #2 lore raw

Re: [PATCH v5 1/7] mips: fix mips_get_syscall_arg() for o32

Quoted 3 lines · Dmitry V. Levin

The first assertion is fixed for mips o32 by using struct pt_regs.pad0 instead of get_user() to obtain syscall arguments. This approach works due to this piece in arch/mips/kernel/scall32-o32.S:

I've had a look now and I can see what's going on here.

The thing is we're trying to access another task's context and obviously
dereferencing $sp obtained from it is not going to work via get_user(), because that just peeks at the current task's context. It often does not crash, because the default user stack always gets assigned the same VMA, but it is pure luck which we wouldn't have if the stack was switched (via setcontext(3) or however) or say a non-default process's thread peeked at, and in any case irrelevant data is obtained just as observed with the test case.

We ought to be using access_remote_vm() to retrieve the other task's
stack contents, but given that the data has been already obtained and saved in `struct pt_regs' it would be an overkill.

So I think your change is actually the correct thing to do, but please
let's not abuse a struct member called `pad', the name of which indicates its contents are not supposed to be of any use. I have therefore posted a preparatory cleanup[1]. May you please rebase your patch on top of that and also update the change description so as to reflect the findings?

Thomas, can you please apply my cleanup soon and ahead of Dmitry's change
so as to make things easy to proceed with? Or otherwise let me know what works for you best.

Also I have a suspicion this stuff ought to be backported, but I guess it
can be decided later on.

Thank you for your patience.

[1] "MIPS: Export syscall stack arguments properly for remote use",

    <https://lore.kernel.org/linux-mips/[email protected]/>

Maciej

Dmitry V. Levin

author

2025-02-11 22:03 UTC #3 lore raw

Re: [PATCH v5 1/7] mips: fix mips_get_syscall_arg() for o32

Quoted 31 lines · Maciej W. Rozycki

Quoted 3 lines · Dmitry V. Levin
The first assertion is fixed for mips o32 by using struct pt_regs.pad0 instead of get_user() to obtain syscall arguments. This approach works due to this piece in arch/mips/kernel/scall32-o32.S:
I've had a look now and I can see what's going on here.
The thing is we're trying to access another task's context and obviously
dereferencing $sp obtained from it is not going to work via get_user(), because that just peeks at the current task's context. It often does not crash, because the default user stack always gets assigned the same VMA, but it is pure luck which we wouldn't have if the stack was switched (via setcontext(3) or however) or say a non-default process's thread peeked at, and in any case irrelevant data is obtained just as observed with the test case.
We ought to be using access_remote_vm() to retrieve the other task's
stack contents, but given that the data has been already obtained and saved in `struct pt_regs' it would be an overkill.
So I think your change is actually the correct thing to do, but please
let's not abuse a struct member called `pad', the name of which indicates its contents are not supposed to be of any use. I have therefore posted a preparatory cleanup[1]. May you please rebase your patch on top of that and also update the change description so as to reflect the findings?
Thomas, can you please apply my cleanup soon and ahead of Dmitry's change
so as to make things easy to proceed with? Or otherwise let me know what works for you best.

Quoted 7 lines

Also I have a suspicion this stuff ought to be backported, but I guess it
can be decided later on.
Thank you for your patience.
[1] "MIPS: Export syscall stack arguments properly for remote use",
    <https://lore.kernel.org/linux-mips/[email protected]/>

Thanks for the analysis, I'm going to rebase my fix and send it as a follow-up to your cleanup patch.

Signature · 1 line

ldv

Dmitry V. Levin

author

2025-02-10 11:34 UTC #4 lore raw

PATCH v5 2/7 hexagon: add syscall_set_return_value()

In reply to Dmitry V. Levin

hexagon is the only architecture that provides HAVE_ARCH_TRACEHOOK but doesn't define syscall_set_return_value(). Since this function is going to be needed on all HAVE_ARCH_TRACEHOOK architectures to implement PTRACE_SET_SYSCALL_INFO API, add it on hexagon, too.

Signed-off-by Dmitry V. Levin <[email protected]>

---
 arch/hexagon/include/asm/syscall.h | 7 +++++++
 1 file changed, 7 insertions(+)

arch/hexagon/include/asm/syscall.h +7 -0

index f6e454f18038..951ca0ed8376 100644
@@ -45,6 +45,13 @@ static inline long syscall_get_return_value(struct task_struct *task,
 	return regs->r00;
 }
 
+static inline void syscall_set_return_value(struct task_struct *task,
+					    struct pt_regs *regs,
+					    int error, long val)
+{
+	regs->r00 = (long) error ?: val;
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_HEXAGON;

Signature · 1 line

ldv

Dmitry V. Levin

author

2025-02-10 11:34 UTC #5 lore raw

PATCH v5 3/7 syscall.h: add syscall_set_arguments()

In reply to Dmitry V. Levin

This function is going to be needed on all HAVE_ARCH_TRACEHOOK architectures to implement PTRACE_SET_SYSCALL_INFO API.

This partially reverts commit 7962c2eddbfe ("arch: remove unused function syscall_set_arguments()") by reusing some of old syscall_set_arguments() implementations.

Signed-off-by Dmitry V. Levin <[email protected]>

Tested-by Charlie Jenkins <[email protected]>

Reviewed-by Charlie Jenkins <[email protected]>

Acked-by Helge Deller <[email protected]> # parisc

---
 arch/arc/include/asm/syscall.h        | 14 +++++++++++
 arch/arm/include/asm/syscall.h        | 13 ++++++++++
 arch/arm64/include/asm/syscall.h      | 13 ++++++++++
 arch/csky/include/asm/syscall.h       | 13 ++++++++++
 arch/hexagon/include/asm/syscall.h    |  7 ++++++
 arch/loongarch/include/asm/syscall.h  |  8 ++++++
 arch/mips/include/asm/syscall.h       | 32 ++++++++++++++++++++++++
 arch/nios2/include/asm/syscall.h      | 11 ++++++++
 arch/openrisc/include/asm/syscall.h   |  7 ++++++
 arch/parisc/include/asm/syscall.h     | 12 +++++++++
 arch/powerpc/include/asm/syscall.h    | 10 ++++++++
 arch/riscv/include/asm/syscall.h      |  9 +++++++
 arch/s390/include/asm/syscall.h       |  9 +++++++
 arch/sh/include/asm/syscall_32.h      | 12 +++++++++
 arch/sparc/include/asm/syscall.h      | 10 ++++++++
 arch/um/include/asm/syscall-generic.h | 14 +++++++++++
 arch/x86/include/asm/syscall.h        | 36 +++++++++++++++++++++++++++
 arch/xtensa/include/asm/syscall.h     | 11 ++++++++
 include/asm-generic/syscall.h         | 16 ++++++++++++
 19 files changed, 257 insertions(+)

arch/arc/include/asm/syscall.h +14 -0

index 9709256e31c8..89c1e1736356 100644
@@ -67,6 +67,20 @@ syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
 	}
 }
 
+static inline void
+syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+		      unsigned long *args)
+{
+	unsigned long *inside_ptregs = &regs->r0;
+	unsigned int n = 6;
+	unsigned int i = 0;
+
+	while (n--) {
+		*inside_ptregs = args[i++];
+		inside_ptregs--;
+	}
+}
+
 static inline int
 syscall_get_arch(struct task_struct *task)
 {

arch/arm/include/asm/syscall.h +13 -0

index fe4326d938c1..21927fa0ae2b 100644
@@ -80,6 +80,19 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(args, &regs->ARM_r0 + 1, 5 * sizeof(args[0]));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	memcpy(&regs->ARM_r0, args, 6 * sizeof(args[0]));
+	/*
+	 * Also copy the first argument into ARM_ORIG_r0
+	 * so that syscall_get_arguments() would return it
+	 * instead of the previous value.
+	 */
+	regs->ARM_ORIG_r0 = regs->ARM_r0;
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	/* ARM tasks don't change audit architectures on the fly. */

arch/arm64/include/asm/syscall.h +13 -0

index ab8e14b96f68..76020b66286b 100644
@@ -73,6 +73,19 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(args, &regs->regs[1], 5 * sizeof(args[0]));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	memcpy(&regs->regs[0], args, 6 * sizeof(args[0]));
+	/*
+	 * Also copy the first argument into orig_x0
+	 * so that syscall_get_arguments() would return it
+	 * instead of the previous value.
+	 */
+	regs->orig_x0 = regs->regs[0];
+}
+
 /*
  * We don't care about endianness (__AUDIT_ARCH_LE bit) here because
  * AArch64 has the same system calls both on little- and big- endian.

arch/csky/include/asm/syscall.h +13 -0

index 0de5734950bf..30403f7a0487 100644
@@ -59,6 +59,19 @@ syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
 	memcpy(args, &regs->a1, 5 * sizeof(args[0]));
 }
 
+static inline void
+syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+		      const unsigned long *args)
+{
+	memcpy(&regs->a0, args, 6 * sizeof(regs->a0));
+	/*
+	 * Also copy the first argument into orig_x0
+	 * so that syscall_get_arguments() would return it
+	 * instead of the previous value.
+	 */
+	regs->orig_a0 = regs->a0;
+}
+
 static inline int
 syscall_get_arch(struct task_struct *task)
 {

arch/hexagon/include/asm/syscall.h +7 -0

index 951ca0ed8376..1024a6548d78 100644
@@ -33,6 +33,13 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(args, &(&regs->r00)[0], 6 * sizeof(args[0]));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	memcpy(&(&regs->r00)[0], args, 6 * sizeof(args[0]));
+}
+
 static inline long syscall_get_error(struct task_struct *task,
 				     struct pt_regs *regs)
 {

arch/loongarch/include/asm/syscall.h +8 -0

index e286dc58476e..ff415b3c0a8e 100644
@@ -61,6 +61,14 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(&args[1], &regs->regs[5], 5 * sizeof(long));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	regs->orig_a0 = args[0];
+	memcpy(&regs->regs[5], &args[1], 5 * sizeof(long));
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_LOONGARCH64;

arch/mips/include/asm/syscall.h +32 -0

index b3f00ede8bb3..2dcc1d01b405 100644
@@ -74,6 +74,23 @@ static inline void mips_get_syscall_arg(unsigned long *arg,
 #endif
 }
 
+static inline void mips_set_syscall_arg(unsigned long *arg,
+	struct task_struct *task, struct pt_regs *regs, unsigned int n)
+{
+#ifdef CONFIG_32BIT
+	switch (n) {
+	case 0: case 1: case 2: case 3:
+		regs->regs[4 + n] = *arg;
+		return;
+	case 4: case 5: case 6: case 7:
+		*arg = regs->pad0[n] = *arg;
+		return;
+	}
+#else
+	regs->regs[4 + n] = *arg;
+#endif
+}
+
 static inline long syscall_get_error(struct task_struct *task,
 				     struct pt_regs *regs)
 {

@@ -120,6 +137,21 @@ static inline void syscall_get_arguments(struct task_struct *task,
 		mips_get_syscall_arg(args++, task, regs, i++);
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	unsigned int i = 0;
+	unsigned int n = 6;
+
+	/* O32 ABI syscall() */
+	if (mips_syscall_is_indirect(task, regs))
+		i++;
+
+	while (n--)
+		mips_set_syscall_arg(args++, task, regs, i++);
+}
+
 extern const unsigned long sys_call_table[];
 extern const unsigned long sys32_call_table[];
 extern const unsigned long sysn32_call_table[];

arch/nios2/include/asm/syscall.h +11 -0

index fff52205fb65..526449edd768 100644
@@ -58,6 +58,17 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	*args   = regs->r9;
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+	struct pt_regs *regs, const unsigned long *args)
+{
+	regs->r4 = *args++;
+	regs->r5 = *args++;
+	regs->r6 = *args++;
+	regs->r7 = *args++;
+	regs->r8 = *args++;
+	regs->r9 = *args;
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_NIOS2;

arch/openrisc/include/asm/syscall.h +7 -0

index 903ed882bdec..e6383be2a195 100644
@@ -57,6 +57,13 @@ syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
 	memcpy(args, &regs->gpr[3], 6 * sizeof(args[0]));
 }
 
+static inline void
+syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+		      const unsigned long *args)
+{
+	memcpy(&regs->gpr[3], args, 6 * sizeof(args[0]));
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_OPENRISC;

arch/parisc/include/asm/syscall.h +12 -0

index 00b127a5e09b..b146d0ae4c77 100644
@@ -29,6 +29,18 @@ static inline void syscall_get_arguments(struct task_struct *tsk,
 	args[0] = regs->gr[26];
 }
 
+static inline void syscall_set_arguments(struct task_struct *tsk,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	regs->gr[21] = args[5];
+	regs->gr[22] = args[4];
+	regs->gr[23] = args[3];
+	regs->gr[24] = args[2];
+	regs->gr[25] = args[1];
+	regs->gr[26] = args[0];
+}
+
 static inline long syscall_get_error(struct task_struct *task,
 				     struct pt_regs *regs)
 {

arch/powerpc/include/asm/syscall.h +10 -0

index 422d7735ace6..521f279e6b33 100644
@@ -114,6 +114,16 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	}
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	memcpy(&regs->gpr[3], args, 6 * sizeof(args[0]));
+
+	/* Also copy the first argument into orig_gpr3 */
+	regs->orig_gpr3 = args[0];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	if (is_tsk_32bit_task(task))

arch/riscv/include/asm/syscall.h +9 -0

index 121fff429dce..8d389ba995c8 100644
@@ -66,6 +66,15 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(args, &regs->a1, 5 * sizeof(args[0]));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	regs->orig_a0 = args[0];
+	args++;
+	memcpy(&regs->a1, args, 5 * sizeof(regs->a1));
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 #ifdef CONFIG_64BIT

arch/s390/include/asm/syscall.h +9 -0

index 27e3d804b311..0e3296a32e6a 100644
@@ -78,6 +78,15 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	args[0] = regs->orig_gpr2 & mask;
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	regs->orig_gpr2 = args[0];
+	for (int n = 1; n < 6; n++)
+		regs->gprs[2 + n] = args[n];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 #ifdef CONFIG_COMPAT

arch/sh/include/asm/syscall_32.h +12 -0

index d87738eebe30..cb51a7528384 100644
@@ -57,6 +57,18 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	args[0] = regs->regs[4];
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	regs->regs[1] = args[5];
+	regs->regs[0] = args[4];
+	regs->regs[7] = args[3];
+	regs->regs[6] = args[2];
+	regs->regs[5] = args[1];
+	regs->regs[4] = args[0];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	int arch = AUDIT_ARCH_SH;

arch/sparc/include/asm/syscall.h +10 -0

index 20c109ac8cc9..62a5a78804c4 100644
@@ -117,6 +117,16 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	}
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	unsigned int i;
+
+	for (i = 0; i < 6; i++)
+		regs->u_regs[UREG_I0 + i] = args[i];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 #if defined(CONFIG_SPARC64) && defined(CONFIG_COMPAT)

arch/um/include/asm/syscall-generic.h +14 -0

index 172b74143c4b..2984feb9d576 100644
@@ -62,6 +62,20 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	*args   = UPT_SYSCALL_ARG6(r);
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	struct uml_pt_regs *r = &regs->regs;
+
+	UPT_SYSCALL_ARG1(r) = *args++;
+	UPT_SYSCALL_ARG2(r) = *args++;
+	UPT_SYSCALL_ARG3(r) = *args++;
+	UPT_SYSCALL_ARG4(r) = *args++;
+	UPT_SYSCALL_ARG5(r) = *args++;
+	UPT_SYSCALL_ARG6(r) = *args;
+}
+
 /* See arch/x86/um/asm/syscall.h for syscall_get_arch() definition. */
 
 #endif	/* __UM_SYSCALL_GENERIC_H */

arch/x86/include/asm/syscall.h +36 -0

index 7c488ff0c764..b9c249dd9e3d 100644
@@ -90,6 +90,18 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	args[5] = regs->bp;
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	regs->bx = args[0];
+	regs->cx = args[1];
+	regs->dx = args[2];
+	regs->si = args[3];
+	regs->di = args[4];
+	regs->bp = args[5];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_I386;

@@ -121,6 +133,30 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	}
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+# ifdef CONFIG_IA32_EMULATION
+	if (task->thread_info.status & TS_COMPAT) {
+		regs->bx = *args++;
+		regs->cx = *args++;
+		regs->dx = *args++;
+		regs->si = *args++;
+		regs->di = *args++;
+		regs->bp = *args;
+	} else
+# endif
+	{
+		regs->di = *args++;
+		regs->si = *args++;
+		regs->dx = *args++;
+		regs->r10 = *args++;
+		regs->r8 = *args++;
+		regs->r9 = *args;
+	}
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	/* x32 tasks should be considered AUDIT_ARCH_X86_64. */

arch/xtensa/include/asm/syscall.h +11 -0

index 5ee974bf8330..f9a671cbf933 100644
@@ -68,6 +68,17 @@ static inline void syscall_get_arguments(struct task_struct *task,
 		args[i] = regs->areg[reg[i]];
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	static const unsigned int reg[] = XTENSA_SYSCALL_ARGUMENT_REGS;
+	unsigned int i;
+
+	for (i = 0; i < 6; ++i)
+		regs->areg[reg[i]] = args[i];
+}
+
 asmlinkage long xtensa_rt_sigreturn(void);
 asmlinkage long xtensa_shmat(int, char __user *, int);
 asmlinkage long xtensa_fadvise64_64(int, int,

include/asm-generic/syscall.h +16 -0

index 182b039ce5fa..292b412f4e9a 100644
@@ -117,6 +117,22 @@ void syscall_set_return_value(struct task_struct *task, struct pt_regs *regs,
 void syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
 			   unsigned long *args);
 
+/**
+ * syscall_set_arguments - change system call parameter value
+ * @task:	task of interest, must be in system call entry tracing
+ * @regs:	task_pt_regs() of @task
+ * @args:	array of argument values to store
+ *
+ * Changes 6 arguments to the system call.
+ * The first argument gets value @args[0], and so on.
+ *
+ * It's only valid to call this when @task is stopped for tracing on
+ * entry to a system call, due to %SYSCALL_WORK_SYSCALL_TRACE or
+ * %SYSCALL_WORK_SYSCALL_AUDIT.
+ */
+void syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+			   const unsigned long *args);
+
 /**
  * syscall_get_arch - return the AUDIT_ARCH for the current system call
  * @task:	task of interest, must be blocked

Signature · 1 line

ldv

Dmitry V. Levin

author

2025-02-10 11:35 UTC #6 lore raw

PATCH v5 4/7 syscall.h: introduce syscall_set_nr()

In reply to Dmitry V. Levin

Similar to syscall_set_arguments() that complements syscall_get_arguments(), introduce syscall_set_nr() that complements syscall_get_nr().

syscall_set_nr() is going to be needed along with syscall_set_arguments() on all HAVE_ARCH_TRACEHOOK architectures to implement PTRACE_SET_SYSCALL_INFO API.

Signed-off-by Dmitry V. Levin <[email protected]>

Tested-by Charlie Jenkins <[email protected]>

Reviewed-by Charlie Jenkins <[email protected]>

Acked-by Helge Deller <[email protected]> # parisc

---
 arch/arc/include/asm/syscall.h        | 11 +++++++++++
 arch/arm/include/asm/syscall.h        | 24 ++++++++++++++++++++++++
 arch/arm64/include/asm/syscall.h      | 16 ++++++++++++++++
 arch/hexagon/include/asm/syscall.h    |  7 +++++++
 arch/loongarch/include/asm/syscall.h  |  7 +++++++
 arch/m68k/include/asm/syscall.h       |  7 +++++++
 arch/microblaze/include/asm/syscall.h |  7 +++++++
 arch/mips/include/asm/syscall.h       | 14 ++++++++++++++
 arch/nios2/include/asm/syscall.h      |  5 +++++
 arch/openrisc/include/asm/syscall.h   |  6 ++++++
 arch/parisc/include/asm/syscall.h     |  7 +++++++
 arch/powerpc/include/asm/syscall.h    | 10 ++++++++++
 arch/riscv/include/asm/syscall.h      |  7 +++++++
 arch/s390/include/asm/syscall.h       | 12 ++++++++++++
 arch/sh/include/asm/syscall_32.h      | 12 ++++++++++++
 arch/sparc/include/asm/syscall.h      | 12 ++++++++++++
 arch/um/include/asm/syscall-generic.h |  5 +++++
 arch/x86/include/asm/syscall.h        |  7 +++++++
 arch/xtensa/include/asm/syscall.h     |  7 +++++++
 include/asm-generic/syscall.h         | 14 ++++++++++++++
 20 files changed, 197 insertions(+)

arch/arc/include/asm/syscall.h +11 -0

index 89c1e1736356..728d625a10f1 100644
@@ -23,6 +23,17 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 		return -1;
 }
 
+static inline void
+syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->r8 = nr;
+}
+
 static inline void
 syscall_rollback(struct task_struct *task, struct pt_regs *regs)
 {

arch/arm/include/asm/syscall.h +24 -0

index 21927fa0ae2b..18b102a30741 100644
@@ -68,6 +68,30 @@ static inline void syscall_set_return_value(struct task_struct *task,
 	regs->ARM_r0 = (long) error ? error : val;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	if (nr == -1) {
+		task_thread_info(task)->abi_syscall = -1;
+		/*
+		 * When the syscall number is set to -1, the syscall will be
+		 * skipped.  In this case the syscall return value has to be
+		 * set explicitly, otherwise the first syscall argument is
+		 * returned as the syscall return value.
+		 */
+		syscall_set_return_value(task, regs, -ENOSYS, 0);
+		return;
+	}
+	if ((IS_ENABLED(CONFIG_AEABI) && !IS_ENABLED(CONFIG_OABI_COMPAT))) {
+		task_thread_info(task)->abi_syscall = nr;
+		return;
+	}
+	task_thread_info(task)->abi_syscall =
+		(task_thread_info(task)->abi_syscall & ~__NR_SYSCALL_MASK) |
+		(nr & __NR_SYSCALL_MASK);
+}
+
 #define SYSCALL_MAX_ARGS 7
 
 static inline void syscall_get_arguments(struct task_struct *task,

arch/arm64/include/asm/syscall.h +16 -0

index 76020b66286b..712daa90e643 100644
@@ -61,6 +61,22 @@ static inline void syscall_set_return_value(struct task_struct *task,
 	regs->regs[0] = val;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->syscallno = nr;
+	if (nr == -1) {
+		/*
+		 * When the syscall number is set to -1, the syscall will be
+		 * skipped.  In this case the syscall return value has to be
+		 * set explicitly, otherwise the first syscall argument is
+		 * returned as the syscall return value.
+		 */
+		syscall_set_return_value(task, regs, -ENOSYS, 0);
+	}
+}
+
 #define SYSCALL_MAX_ARGS 6
 
 static inline void syscall_get_arguments(struct task_struct *task,

arch/hexagon/include/asm/syscall.h +7 -0

index 1024a6548d78..70637261817a 100644
@@ -26,6 +26,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->r06;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->r06 = nr;
+}
+
 static inline void syscall_get_arguments(struct task_struct *task,
 					 struct pt_regs *regs,
 					 unsigned long *args)

arch/loongarch/include/asm/syscall.h +7 -0

index ff415b3c0a8e..81d2733f7b94 100644
@@ -26,6 +26,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->regs[11];
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->regs[11] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/m68k/include/asm/syscall.h +7 -0

index d1453e850cdd..bf84b160c2eb 100644
@@ -14,6 +14,13 @@ static inline int syscall_get_nr(struct task_struct *task,
 	return regs->orig_d0;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->orig_d0 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/microblaze/include/asm/syscall.h +7 -0

index 5eb3f624cc59..b5b6b91fae3e 100644
@@ -14,6 +14,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->r12;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->r12 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/mips/include/asm/syscall.h +14 -0

index 2dcc1d01b405..1cd25306cc13 100644
@@ -41,6 +41,20 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return task_thread_info(task)->syscall;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * New syscall number has to be assigned to regs[2] because
+	 * syscall_trace_entry() loads it from there unconditionally.
+	 *
+	 * Consequently, if the syscall was indirect and nr != __NR_syscall,
+	 * then after this assignment the syscall will cease to be indirect.
+	 */
+	task_thread_info(task)->syscall = regs->regs[2] = nr;
+}
+
 static inline void mips_syscall_update_nr(struct task_struct *task,
 					  struct pt_regs *regs)
 {

arch/nios2/include/asm/syscall.h +5 -0

index 526449edd768..8e3eb1d689bb 100644
@@ -15,6 +15,11 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->r2;
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	regs->r2 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				struct pt_regs *regs)
 {

arch/openrisc/include/asm/syscall.h +6 -0

index e6383be2a195..5e037d9659c5 100644
@@ -25,6 +25,12 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->orig_gpr11;
 }
 
+static inline void
+syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	regs->orig_gpr11 = nr;
+}
+
 static inline void
 syscall_rollback(struct task_struct *task, struct pt_regs *regs)
 {

arch/parisc/include/asm/syscall.h +7 -0

index b146d0ae4c77..c11222798ab2 100644
@@ -17,6 +17,13 @@ static inline long syscall_get_nr(struct task_struct *tsk,
 	return regs->gr[20];
 }
 
+static inline void syscall_set_nr(struct task_struct *tsk,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->gr[20] = nr;
+}
+
 static inline void syscall_get_arguments(struct task_struct *tsk,
 					 struct pt_regs *regs,
 					 unsigned long *args)

arch/powerpc/include/asm/syscall.h +10 -0

index 521f279e6b33..7505dcfed247 100644
@@ -39,6 +39,16 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 		return -1;
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->gpr[0] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/riscv/include/asm/syscall.h +7 -0

index 8d389ba995c8..a5281cdf2b10 100644
@@ -30,6 +30,13 @@ static inline int syscall_get_nr(struct task_struct *task,
 	return regs->a7;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->a7 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/s390/include/asm/syscall.h +12 -0

index 0e3296a32e6a..db6ca55564ff 100644
@@ -24,6 +24,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 		(regs->int_code & 0xffff) : -1;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->int_code = (regs->int_code & ~0xffff) | (nr & 0xffff);
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/sh/include/asm/syscall_32.h +12 -0

index cb51a7528384..7027d87d901d 100644
@@ -15,6 +15,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return (regs->tra >= 0) ? regs->regs[3] : -1L;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->regs[3] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/sparc/include/asm/syscall.h +12 -0

index 62a5a78804c4..b0233924d323 100644
@@ -25,6 +25,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return (syscall_p ? regs->u_regs[UREG_G1] : -1L);
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->u_regs[UREG_G1] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/um/include/asm/syscall-generic.h +5 -0

index 2984feb9d576..bcd73bcfe577 100644
@@ -21,6 +21,11 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return PT_REGS_SYSCALL_NR(regs);
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	PT_REGS_SYSCALL_NR(regs) = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/x86/include/asm/syscall.h +7 -0

index b9c249dd9e3d..c10dbb74cd00 100644
@@ -38,6 +38,13 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->orig_ax;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->orig_ax = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

arch/xtensa/include/asm/syscall.h +7 -0

index f9a671cbf933..7db3b489c8ad 100644
@@ -28,6 +28,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->syscall;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->syscall = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {

include/asm-generic/syscall.h +14 -0

index 292b412f4e9a..c5a3ad53beec 100644
@@ -37,6 +37,20 @@ struct pt_regs;
  */
 int syscall_get_nr(struct task_struct *task, struct pt_regs *regs);
 
+/**
+ * syscall_set_nr - change the system call a task is executing
+ * @task:	task of interest, must be blocked
+ * @regs:	task_pt_regs() of @task
+ * @nr:		system call number
+ *
+ * Changes the system call number @task is about to execute.
+ *
+ * It's only valid to call this when @task is stopped for tracing on
+ * entry to a system call, due to %SYSCALL_WORK_SYSCALL_TRACE or
+ * %SYSCALL_WORK_SYSCALL_AUDIT.
+ */
+void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr);
+
 /**
  * syscall_rollback - roll back registers after an aborted system call
  * @task:	task of interest, must be in system call exit tracing

Signature · 1 line

ldv

Dmitry V. Levin

author

2025-02-10 11:35 UTC #7 lore raw

PATCH v5 5/7 ptrace_get_syscall_info: factor out ptrace_get_syscall_info_op

In reply to Dmitry V. Levin

Move the code that calculates the type of the system call stop out of ptrace_get_syscall_info() into a separate function ptrace_get_syscall_info_op() which is going to be used later to implement PTRACE_SET_SYSCALL_INFO API.

Signed-off-by Dmitry V. Levin <[email protected]>

Reviewed-by Oleg Nesterov <[email protected]>

---
 kernel/ptrace.c | 58 +++++++++++++++++++++++++++++--------------------
 1 file changed, 34 insertions(+), 24 deletions(-)

kernel/ptrace.c +34 ~~-24~~

index d5f89f9ef29f..22e7d74cf4cd 100644
@@ -921,7 +921,6 @@ ptrace_get_syscall_info_entry(struct task_struct *child, struct pt_regs *regs,
 	unsigned long args[ARRAY_SIZE(info->entry.args)];
 	int i;
 
-	info->op = PTRACE_SYSCALL_INFO_ENTRY;
 	info->entry.nr = syscall_get_nr(child, regs);
 	syscall_get_arguments(child, regs, args);
 	for (i = 0; i < ARRAY_SIZE(args); i++)

@@ -943,7 +942,6 @@ ptrace_get_syscall_info_seccomp(struct task_struct *child, struct pt_regs *regs,
 	 * diverge significantly enough.
 	 */
 	ptrace_get_syscall_info_entry(child, regs, info);
-	info->op = PTRACE_SYSCALL_INFO_SECCOMP;
 	info->seccomp.ret_data = child->ptrace_message;
 
 	/* ret_data is the last field in struct ptrace_syscall_info.seccomp */

@@ -954,7 +952,6 @@ static unsigned long
 ptrace_get_syscall_info_exit(struct task_struct *child, struct pt_regs *regs,
 			     struct ptrace_syscall_info *info)
 {
-	info->op = PTRACE_SYSCALL_INFO_EXIT;
 	info->exit.rval = syscall_get_error(child, regs);
 	info->exit.is_error = !!info->exit.rval;
 	if (!info->exit.is_error)

@@ -965,19 +962,8 @@ ptrace_get_syscall_info_exit(struct task_struct *child, struct pt_regs *regs,
 }
 
 static int
-ptrace_get_syscall_info(struct task_struct *child, unsigned long user_size,
-			void __user *datavp)
+ptrace_get_syscall_info_op(struct task_struct *child)
 {
-	struct pt_regs *regs = task_pt_regs(child);
-	struct ptrace_syscall_info info = {
-		.op = PTRACE_SYSCALL_INFO_NONE,
-		.arch = syscall_get_arch(child),
-		.instruction_pointer = instruction_pointer(regs),
-		.stack_pointer = user_stack_pointer(regs),
-	};
-	unsigned long actual_size = offsetof(struct ptrace_syscall_info, entry);
-	unsigned long write_size;
-
 	/*
 	 * This does not need lock_task_sighand() to access
 	 * child->last_siginfo because ptrace_freeze_traced()

@@ -988,18 +974,42 @@ ptrace_get_syscall_info(struct task_struct *child, unsigned long user_size,
 	case SIGTRAP | 0x80:
 		switch (child->ptrace_message) {
 		case PTRACE_EVENTMSG_SYSCALL_ENTRY:
-			actual_size = ptrace_get_syscall_info_entry(child, regs,
-								    &info);
-			break;
+			return PTRACE_SYSCALL_INFO_ENTRY;
 		case PTRACE_EVENTMSG_SYSCALL_EXIT:
-			actual_size = ptrace_get_syscall_info_exit(child, regs,
-								   &info);
-			break;
+			return PTRACE_SYSCALL_INFO_EXIT;
+		default:
+			return PTRACE_SYSCALL_INFO_NONE;
 		}
-		break;
 	case SIGTRAP | (PTRACE_EVENT_SECCOMP << 8):
-		actual_size = ptrace_get_syscall_info_seccomp(child, regs,
-							      &info);
+		return PTRACE_SYSCALL_INFO_SECCOMP;
+	default:
+		return PTRACE_SYSCALL_INFO_NONE;
+	}
+}
+
+static int
+ptrace_get_syscall_info(struct task_struct *child, unsigned long user_size,
+			void __user *datavp)
+{
+	struct pt_regs *regs = task_pt_regs(child);
+	struct ptrace_syscall_info info = {
+		.op = ptrace_get_syscall_info_op(child),
+		.arch = syscall_get_arch(child),
+		.instruction_pointer = instruction_pointer(regs),
+		.stack_pointer = user_stack_pointer(regs),
+	};
+	unsigned long actual_size = offsetof(struct ptrace_syscall_info, entry);
+	unsigned long write_size;
+
+	switch (info.op) {
+	case PTRACE_SYSCALL_INFO_ENTRY:
+		actual_size = ptrace_get_syscall_info_entry(child, regs, &info);
+		break;
+	case PTRACE_SYSCALL_INFO_EXIT:
+		actual_size = ptrace_get_syscall_info_exit(child, regs, &info);
+		break;
+	case PTRACE_SYSCALL_INFO_SECCOMP:
+		actual_size = ptrace_get_syscall_info_seccomp(child, regs, &info);
 		break;
 	}

Signature · 1 line

ldv

Dmitry V. Levin

author

2025-02-10 11:35 UTC #8 lore raw

PATCH v5 6/7 ptrace: introduce PTRACE_SET_SYSCALL_INFO request

In reply to Dmitry V. Levin

PTRACE_SET_SYSCALL_INFO is a generic ptrace API that complements PTRACE_GET_SYSCALL_INFO by letting the ptracer modify details of system calls the tracee is blocked in.

ptrace(2) man page:

Link https://lore.kernel.org/all/[email protected]/ open here

Signed-off-by Dmitry V. Levin <[email protected]>

Reviewed-by Alexey Gladkov <[email protected]>

Reviewed-by Charlie Jenkins <[email protected]>

Tested-by Charlie Jenkins <[email protected]>

Reviewed-by Eugene Syromiatnikov <[email protected]>

Reviewed-by Oleg Nesterov <[email protected]>

---
 include/uapi/linux/ptrace.h |   7 ++-
 kernel/ptrace.c             | 121 +++++++++++++++++++++++++++++++++++-
 2 files changed, 126 insertions(+), 2 deletions(-)

include/uapi/linux/ptrace.h +6 -1

index 72c038fc71d0..5f8ef6156752 100644
@@ -74,6 +74,7 @@ struct seccomp_metadata {
 };
 
 #define PTRACE_GET_SYSCALL_INFO		0x420e
+#define PTRACE_SET_SYSCALL_INFO		0x4212
 #define PTRACE_SYSCALL_INFO_NONE	0
 #define PTRACE_SYSCALL_INFO_ENTRY	1
 #define PTRACE_SYSCALL_INFO_EXIT	2

@@ -81,7 +82,8 @@ struct seccomp_metadata {
 
 struct ptrace_syscall_info {
 	__u8 op;	/* PTRACE_SYSCALL_INFO_* */
-	__u8 pad[3];
+	__u8 reserved;
+	__u16 flags;
 	__u32 arch;
 	__u64 instruction_pointer;
 	__u64 stack_pointer;

@@ -98,6 +100,7 @@ struct ptrace_syscall_info {
 			__u64 nr;
 			__u64 args[6];
 			__u32 ret_data;
+			__u32 reserved2;
 		} seccomp;
 	};
 };

@@ -142,6 +145,8 @@ struct ptrace_sud_config {
 	__u64 len;
 };
 
+/* 0x4212 is PTRACE_SET_SYSCALL_INFO */
+
 /*
  * These values are stored in task->ptrace_message
  * by ptrace_stop to describe the current syscall-stop.

kernel/ptrace.c +120 -1

139 lines not on this page · raw message

Signature · 1 line

ldv

Dmitry V. Levin

author

2025-02-10 11:35 UTC #9 lore raw

PATCH v5 7/7 selftests/ptrace: add a test case for PTRACE_SET_SYSCALL_INFO

In reply to Dmitry V. Levin

Check whether PTRACE_SET_SYSCALL_INFO semantics implemented in the kernel matches userspace expectations.

Signed-off-by Dmitry V. Levin <[email protected]>

Reviewed-by Oleg Nesterov <[email protected]>

---
 tools/testing/selftests/ptrace/Makefile       |   2 +-
 .../selftests/ptrace/set_syscall_info.c       | 519 ++++++++++++++++++
 2 files changed, 520 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/ptrace/set_syscall_info.c

tools/testing/selftests/ptrace/Makefile +1 -1

index 1c631740a730..c5e0b76ba6ac 100644
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 CFLAGS += -std=c99 -pthread -Wall $(KHDR_INCLUDES)
 
-TEST_GEN_PROGS := get_syscall_info peeksiginfo vmaccess get_set_sud
+TEST_GEN_PROGS := get_syscall_info set_syscall_info peeksiginfo vmaccess get_set_sud
 
 include ../lib.mk

tools/testing/selftests/ptrace/set_syscall_info.c new file +519 -0

519 lines not on this page · raw message

Signature · 1 line

ldv