powerpc, mm: Memory Protection Keys

Memory protection keys enable applications to protect its address space from inadvertent access from or corruption by itself.

These patches along with the pte-bit freeing patch series enables the protection key feature on powerpc; 4k and 64k hashpage kernels.

Will send the documentation and selftest patches separately

All patches can be found at --
https://github.com/rampai/memorykeys.git memkey.v10

The overall idea:
-----------------
A process allocates a key and associates it with an address range within its address space. The process then can dynamically set read/write permissions on the key without involving the kernel. Any code that violates the permissions of the address space; as defined by its associated key, will receive a segmentation fault.

This patch series enables the feature on PPC64 HPTE platform.

ISA3.0 section 5.7.13 describes the detailed
specifications.

Highlevel view of the design:
---------------------------
When an application associates a key with a address address range, program the key in the Linux PTE. When the MMU detects a page fault, allocate a hash page and program the key into HPTE. And finally when the MMU detects a key violation; due to invalid application access, invoke the registered signal handler and provide the violated key number.

Testing:
-------
This patch series has passed all the protection key tests available in the selftest directory.The tests are updated to work on both x86 and powerpc. The selftests have passed on x86 and powerpc hardware.

History:
-------
version v10:
(1) key-fault in page-fault handler is handled as normal fault and not as a bad fault.
(2) changed device tree scanning to unflattened device tree.
(3) fixed a bug in the logic that detected the total number of available pkeys.
(4) dropped two patches. (i) sysfs interface (ii) sys_pkey_modif() syscall

version v9:
(1) used jump-labels to optimize code -- Balbir
(2) fixed a register initialization bug noted by Balbir
(3) fixed inappropriate use of paca to pass siginfo and keys to signal handler
(4) Cleanup of comment style not to be right justified -- mpe
(5) restructured the patches to depend on the availability of VM_PKEY_BIT4 in include/linux/mm.h
(6) Incorporated comments from Dave Hansen towards changes to selftest and got them tested on x86.

version v8:
(1) Contents of the AMR register withdrawn from the siginfo structure. Applications can always read the AMR register.
(2) AMR/IAMR/UAMOR are now available through ptrace system call. -- thanks to Thiago
(3) code changes to handle legacy power cpus that do not support execute-disable.
(4) incorporates many code improvement suggestions.

version v7:
(1) refers to device tree property to enable protection keys.
(2) adds 4K PTE support.
(3) fixes a couple of bugs noticed by Thiago
(4) decouples this patch series from arch- independent code. This patch series can now stand by itself, with one kludge
patch(2).
version v7:
(1) refers to device tree property to enable protection keys.
(2) adds 4K PTE support.
(3) fixes a couple of bugs noticed by Thiago
(4) decouples this patch series from arch- independent code. This patch series can now stand by itself, with one kludge patch(2).

version v6:
(1) selftest changes are broken down into 20 incremental patches.
(2) A separate key allocation mask that includes PKEY_DISABLE_EXECUTE is added for powerpc
(3) pkey feature is enabled for 64K HPT case only. RPT and 4k HPT is disabled.
(4) Documentation is updated to better capture the semantics.
(5) introduced arch_pkeys_enabled() to find if an arch enables pkeys. Correspond- ing change the logic that displays key value in smaps.
(6) code rearranged in many places based on comments from Dave Hansen, Balbir, Anshuman.
(7) fixed one bug where a bogus key could be associated successfully in pkey_mprotect().

version v5:
(1) reverted back to the old design -- store the key in the pte, instead of bypassing it. The v4 design slowed down the hash page path.
(2) detects key violation when kernel is told to access user pages.
(3) further refined the patches into smaller consumable units
(4) page faults handlers captures the fault- ing key
from the pte instead of the vma. This closes a race between where the key update in the vma and a key fault caused by the key programmed in the pte.
(5) a key created with access-denied should also set it up to deny write. Fixed it.
(6) protection-key number is displayed in smaps the x86 way.

version v4:
(1) patches no more depend on the pte bits to program the hpte
-- comment by Balbir
(2) documentation updates
(3) fixed a bug in the selftest.
(4) unlike x86, powerpc lets signal handler change key permission bits; the change will persist across signal handler boundaries. Earlier we allowed the signal handler to modify a field in the siginfo structure which would than be used by the kernel to program the key protection register (AMR) -- resolves a issue raised by Ben. "Calls to sys_swapcontext with a made-up context will end up with a crap AMR if done by code who didn't know about that register".
(5) these changes enable protection keys on 4k-page kernel aswell.

version v3:
(1) split the patches into smaller consumable patches.
(2) added the ability to disable execute permission on a key at creation.
(3) rename calc_pte_to_hpte_pkey_bits() to pte_to_hpte_pkey_bits()
-- suggested by Anshuman
(4) some code optimization and clarity in do_page_fault()
(5) A bug fix while invalidating a hpte slot in __hash_page_4K()
-- noticed by Aneesh

version v2:
(1) documentation and selftest added.
(2) fixed a bug in 4k hpte backed 64k pte where page invalidation was not done correctly, and initialization of second-part-of-the-pte was not done correctly if the pte was not yet Hashed with a hpte.
-- Reported by Aneesh.
(3) Fixed ABI breakage caused in siginfo structure.
-- Reported by Anshuman.

version v1: Initial version

Ram Pai (26):
mm, powerpc, x86: define VM_PKEY_BITx bits if CONFIG_ARCH_HAS_PKEYS
is enabled
mm, powerpc, x86: introduce an additional vma bit for powerpc pkey
powerpc: initial pkey plumbing
powerpc: track allocation status of all pkeys
powerpc: helper function to read,write AMR,IAMR,UAMOR registers
powerpc: helper functions to initialize AMR, IAMR and UAMOR registers
powerpc: cleanup AMR, IAMR when a key is allocated or freed
powerpc: implementation for arch_set_user_pkey_access()
powerpc: ability to create execute-disabled pkeys
powerpc: store and restore the pkey state across context switches
powerpc: introduce execute-only pkey
powerpc: ability to associate pkey to a vma
powerpc: implementation for arch_override_mprotect_pkey()
powerpc: map vma key-protection bits to pte key bits.
powerpc: Program HPTE key protection bits
powerpc: helper to validate key-access permissions of a pte
powerpc: check key protection for user page access
powerpc: implementation for arch_vma_access_permitted()
powerpc: Handle exceptions caused by pkey violation
powerpc: introduce get_mm_addr_key() helper
powerpc: Deliver SEGV signal on pkey violation
powerpc: Enable pkey subsystem
powerpc: sys_pkey_alloc() and sys_pkey_free() system calls
powerpc: sys_pkey_mprotect() system call
mm, x86 : introduce arch_pkeys_enabled()
mm: display pkey in smaps if arch_pkeys_enabled() is true

Thiago Jung Bauermann (1):
powerpc/ptrace: Add memory protection key regset

 arch/powerpc/Kconfig                          |   15 +
 arch/powerpc/include/asm/book3s/64/mmu-hash.h |    5 +
 arch/powerpc/include/asm/book3s/64/mmu.h      |   10 +
 arch/powerpc/include/asm/book3s/64/pgtable.h  |   48 +++-
 arch/powerpc/include/asm/bug.h                |    1 +
 arch/powerpc/include/asm/cputable.h           |   16 +-
 arch/powerpc/include/asm/mman.h               |   13 +-
 arch/powerpc/include/asm/mmu.h                |    9 +
 arch/powerpc/include/asm/mmu_context.h        |   22 ++
 arch/powerpc/include/asm/pkeys.h              |  229 ++++++++++++
 arch/powerpc/include/asm/processor.h          |    5 +
 arch/powerpc/include/asm/reg.h                |    1 -
 arch/powerpc/include/asm/systbl.h             |    3 +
 arch/powerpc/include/asm/unistd.h             |    6 +-
 arch/powerpc/include/uapi/asm/elf.h           |    1 +
 arch/powerpc/include/uapi/asm/mman.h          |    6 +
 arch/powerpc/include/uapi/asm/unistd.h        |    3 +
 arch/powerpc/kernel/exceptions-64s.S          |    2 +-
 arch/powerpc/kernel/process.c                 |    7 +
 arch/powerpc/kernel/ptrace.c                  |   66 ++++
 arch/powerpc/kernel/traps.c                   |   19 +-
 arch/powerpc/mm/Makefile                      |    1 +
 arch/powerpc/mm/fault.c                       |   49 +++-
 arch/powerpc/mm/hash_utils_64.c               |   26 ++
 arch/powerpc/mm/mmu_context_book3s64.c        |    2 +
 arch/powerpc/mm/pkeys.c                       |  469 +++++++++++++++++++++++++
 arch/x86/include/asm/pkeys.h                  |    1 +
 arch/x86/kernel/fpu/xstate.c                  |    5 +
 arch/x86/kernel/setup.c                       |    8 -
 fs/proc/task_mmu.c                            |   16 +-
 include/linux/mm.h                            |   12 +-
 include/linux/pkeys.h                         |    5 +
 include/uapi/linux/elf.h                      |    1 +
 33 files changed, 1040 insertions(+), 42 deletions(-)
 create mode 100644 arch/powerpc/include/asm/pkeys.h
 create mode 100644 arch/powerpc/mm/pkeys.c

VM_PKEY_BITx are defined only if CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS is enabled. Powerpc also needs these bits. Hence lets define the VM_PKEY_BITx bits for any architecture that enables CONFIG_ARCH_HAS_PKEYS.

---
 fs/proc/task_mmu.c |    4 ++--
 include/linux/mm.h |    9 +++++----
 2 files changed, 7 insertions(+), 6 deletions(-)

index 339e4c1..b139617 100644
@@ -674,13 +674,13 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 		[ilog2(VM_MERGEABLE)]	= "mg",
 		[ilog2(VM_UFFD_MISSING)]= "um",
 		[ilog2(VM_UFFD_WP)]	= "uw",
-#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+#ifdef CONFIG_ARCH_HAS_PKEYS
 		/* These come out via ProtectionKey: */
 		[ilog2(VM_PKEY_BIT0)]	= "",
 		[ilog2(VM_PKEY_BIT1)]	= "",
 		[ilog2(VM_PKEY_BIT2)]	= "",
 		[ilog2(VM_PKEY_BIT3)]	= "",
-#endif
+#endif /* CONFIG_ARCH_HAS_PKEYS */
 	};
 	size_t i;
 

index ea818ff..01381d3 100644
@@ -228,15 +228,16 @@ extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
 #define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
 #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
 
-#if defined(CONFIG_X86)
-# define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
-#if defined (CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS)
+#ifdef CONFIG_ARCH_HAS_PKEYS
 # define VM_PKEY_SHIFT	VM_HIGH_ARCH_BIT_0
 # define VM_PKEY_BIT0	VM_HIGH_ARCH_0	/* A protection key is a 4-bit value */
 # define VM_PKEY_BIT1	VM_HIGH_ARCH_1
 # define VM_PKEY_BIT2	VM_HIGH_ARCH_2
 # define VM_PKEY_BIT3	VM_HIGH_ARCH_3
-#endif
+#endif /* CONFIG_ARCH_HAS_PKEYS */
+
+#if defined(CONFIG_X86)
+# define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
 #elif defined(CONFIG_PPC)
 # define VM_SAO		VM_ARCH_1	/* Strong Access Ordering (powerpc) */
 #elif defined(CONFIG_PARISC)

1.7.1

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Currently only 4bits are allocated in the vma flags to hold 16 keys. This is sufficient for x86. PowerPC supports 32 keys, which needs 5bits. This patch allocates an additional bit.

---
 fs/proc/task_mmu.c |    1 +
 include/linux/mm.h |    3 ++-
 2 files changed, 3 insertions(+), 1 deletions(-)

index b139617..0edd4da 100644
@@ -680,6 +680,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 		[ilog2(VM_PKEY_BIT1)]	= "",
 		[ilog2(VM_PKEY_BIT2)]	= "",
 		[ilog2(VM_PKEY_BIT3)]	= "",
+		[ilog2(VM_PKEY_BIT4)]	= "",
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 	};
 	size_t i;

index 01381d3..ebcb997 100644
@@ -231,9 +231,10 @@ extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
 #ifdef CONFIG_ARCH_HAS_PKEYS
 # define VM_PKEY_SHIFT	VM_HIGH_ARCH_BIT_0
 # define VM_PKEY_BIT0	VM_HIGH_ARCH_0	/* A protection key is a 4-bit value */
-# define VM_PKEY_BIT1	VM_HIGH_ARCH_1
+# define VM_PKEY_BIT1	VM_HIGH_ARCH_1	/* on x86 and 5-bit value on ppc64   */
 # define VM_PKEY_BIT2	VM_HIGH_ARCH_2
 # define VM_PKEY_BIT3	VM_HIGH_ARCH_3
+# define VM_PKEY_BIT4	VM_HIGH_ARCH_4
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 
 #if defined(CONFIG_X86)

1.7.1

Sorry please ignore this series. It was a duplication mistake. I aborted the send midway, but a few escaped into the cyber.

RP

Ram Pai