From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> This establishes two more system calls for protection key management: unsigned long pkey_get(int pkey); int pkey_set(int pkey, unsigned long access_rights); The return value from pkey_get() and the 'access_rights' passed to pkey_set() are the same format: a bitmask containing PKEY_DENY_WRITE and/or PKEY_DENY_ACCESS, or nothing set at all. These can replace userspace's direct use of the new rdpkru/wrpkru instructions. With current hardware, the kernel can not enforce that it has control over a given key. But, this at least allows the kernel to indicate to userspace that userspace does not control a given protection key. This makes it more likely that situations like using a pkey after sys_pkey_free() can be detected. The kernel does _not_ enforce that this interface must be used for changes to PKRU, whether or not a key has been "allocated". This syscall interface could also theoretically be replaced with a pair of vsyscalls. The vsyscalls would just call WRPKRU/RDPKRU directly in situations where they are drop-in equivalents for what the kernel would be doing. Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: linux-api@xxxxxxxxxxxxxxx Cc: linux-mm@xxxxxxxxx Cc: x86@xxxxxxxxxx Cc: torvalds@xxxxxxxxxxxxxxxxxxxx Cc: akpm@xxxxxxxxxxxxxxxxxxxx --- b/arch/x86/entry/syscalls/syscall_32.tbl | 2 + b/arch/x86/entry/syscalls/syscall_64.tbl | 2 + b/arch/x86/include/asm/pkeys.h | 4 +- b/arch/x86/kernel/fpu/xstate.c | 55 +++++++++++++++++++++++++++++-- b/include/linux/pkeys.h | 8 ++++ b/mm/mprotect.c | 41 +++++++++++++++++++++++ 6 files changed, 109 insertions(+), 3 deletions(-) diff -puN arch/x86/entry/syscalls/syscall_32.tbl~pkeys-118-syscalls-set-get arch/x86/entry/syscalls/syscall_32.tbl --- a/arch/x86/entry/syscalls/syscall_32.tbl~pkeys-118-syscalls-set-get 2016-06-08 16:26:35.894970089 -0700 +++ b/arch/x86/entry/syscalls/syscall_32.tbl 2016-06-08 16:26:35.906970634 -0700 @@ -389,3 +389,5 @@ 380 i386 pkey_mprotect sys_pkey_mprotect 381 i386 pkey_alloc sys_pkey_alloc 382 i386 pkey_free sys_pkey_free +383 i386 pkey_get sys_pkey_get +384 i386 pkey_set sys_pkey_set diff -puN arch/x86/entry/syscalls/syscall_64.tbl~pkeys-118-syscalls-set-get arch/x86/entry/syscalls/syscall_64.tbl --- a/arch/x86/entry/syscalls/syscall_64.tbl~pkeys-118-syscalls-set-get 2016-06-08 16:26:35.896970180 -0700 +++ b/arch/x86/entry/syscalls/syscall_64.tbl 2016-06-08 16:26:35.906970634 -0700 @@ -338,6 +338,8 @@ 329 common pkey_mprotect sys_pkey_mprotect 330 common pkey_alloc sys_pkey_alloc 331 common pkey_free sys_pkey_free +332 common pkey_get sys_pkey_get +333 common pkey_set sys_pkey_set # # x32-specific system call numbers start at 512 to avoid cache impact diff -puN arch/x86/include/asm/pkeys.h~pkeys-118-syscalls-set-get arch/x86/include/asm/pkeys.h --- a/arch/x86/include/asm/pkeys.h~pkeys-118-syscalls-set-get 2016-06-08 16:26:35.898970271 -0700 +++ b/arch/x86/include/asm/pkeys.h 2016-06-08 16:26:35.908970724 -0700 @@ -56,7 +56,7 @@ static inline bool validate_pkey(int pke } static inline -bool mm_pkey_is_allocated(struct mm_struct *mm, unsigned long pkey) +bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) { if (!validate_pkey(pkey)) return true; @@ -107,4 +107,6 @@ extern int arch_set_user_pkey_access(str extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long init_val); +extern unsigned long arch_get_user_pkey_access(struct task_struct *tsk, + int pkey); #endif /*_ASM_X86_PKEYS_H */ diff -puN arch/x86/kernel/fpu/xstate.c~pkeys-118-syscalls-set-get arch/x86/kernel/fpu/xstate.c --- a/arch/x86/kernel/fpu/xstate.c~pkeys-118-syscalls-set-get 2016-06-08 16:26:35.899970316 -0700 +++ b/arch/x86/kernel/fpu/xstate.c 2016-06-08 16:26:35.908970724 -0700 @@ -690,7 +690,7 @@ void fpu__resume_cpu(void) * * Note: does not work for compacted buffers. */ -void *__raw_xsave_addr(struct xregs_state *xsave, int xstate_feature_mask) +static void *__raw_xsave_addr(struct xregs_state *xsave, int xstate_feature_mask) { int feature_nr = fls64(xstate_feature_mask) - 1; @@ -864,6 +864,7 @@ out: #define NR_VALID_PKRU_BITS (CONFIG_NR_PROTECTION_KEYS * 2) #define PKRU_VALID_MASK (NR_VALID_PKRU_BITS - 1) +#define PKRU_INIT_STATE 0 /* * This will go out and modify the XSAVE buffer so that PKRU is @@ -882,6 +883,9 @@ int __arch_set_user_pkey_access(struct t int pkey_shift = (pkey * PKRU_BITS_PER_PKEY); u32 new_pkru_bits = 0; + /* Only support manipulating current task for now */ + if (tsk != current) + return -EINVAL; /* * This check implies XSAVE support. OSPKE only gets * set if we enable XSAVE and we enable PKU in XCR0. @@ -907,7 +911,7 @@ int __arch_set_user_pkey_access(struct t * state. */ if (!old_pkru_state) - new_pkru_state.pkru = 0; + new_pkru_state.pkru = PKRU_INIT_STATE; else new_pkru_state.pkru = old_pkru_state->pkru; @@ -945,4 +949,51 @@ int arch_set_user_pkey_access(struct tas return -EINVAL; return __arch_set_user_pkey_access(tsk, pkey, init_val); } + +/* + * Figures out what the rights are currently for 'pkey'. + * Converts from PKRU's format to the user-visible PKEY_DISABLE_* + * format. + */ +unsigned long arch_get_user_pkey_access(struct task_struct *tsk, int pkey) +{ + struct fpu *fpu = ¤t->thread.fpu; + u32 pkru_reg; + int ret = 0; + + /* Only support manipulating current task for now */ + if (tsk != current) + return -1; + if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) + return -1; + /* + * The contents of PKRU itself are invalid. Consult the + * task's XSAVE buffer for PKRU contents. This is much + * more expensive than reading PKRU directly, but should + * be rare or impossible with eagerfpu mode. + */ + if (!fpu->fpregs_active) { + struct xregs_state *xsave = &fpu->state.xsave; + struct pkru_state *pkru_state = + get_xsave_addr(xsave, XFEATURE_MASK_PKRU); + /* + * PKRU is in its init state and not present in + * the buffer in a saved form. + */ + if (!pkru_state) + return PKRU_INIT_STATE; + + return pkru_state->pkru; + } + /* + * Consult the user register directly. + */ + pkru_reg = read_pkru(); + if (!__pkru_allows_read(pkru_reg, pkey)) + ret |= PKEY_DISABLE_ACCESS; + if (!__pkru_allows_write(pkru_reg, pkey)) + ret |= PKEY_DISABLE_WRITE; + + return ret; +} #endif /* CONFIG_ARCH_HAS_PKEYS */ diff -puN include/linux/pkeys.h~pkeys-118-syscalls-set-get include/linux/pkeys.h --- a/include/linux/pkeys.h~pkeys-118-syscalls-set-get 2016-06-08 16:26:35.901970407 -0700 +++ b/include/linux/pkeys.h 2016-06-08 16:26:35.909970770 -0700 @@ -44,6 +44,14 @@ static inline int mm_pkey_free(struct mm static inline int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long init_val) { + return -EINVAL; +} + +static inline +unsigned long arch_get_user_pkey_access(struct task_struct *tsk, int pkey) +{ + if (pkey) + return -1; return 0; } diff -puN mm/mprotect.c~pkeys-118-syscalls-set-get mm/mprotect.c --- a/mm/mprotect.c~pkeys-118-syscalls-set-get 2016-06-08 16:26:35.903970497 -0700 +++ b/mm/mprotect.c 2016-06-08 16:26:35.909970770 -0700 @@ -537,3 +537,44 @@ SYSCALL_DEFINE1(pkey_free, int, pkey) */ return ret; } + +SYSCALL_DEFINE2(pkey_get, int, pkey, unsigned long, flags) +{ + unsigned long ret = 0; + + if (flags) + return -EINVAL; + + down_write(¤t->mm->mmap_sem); + if (!mm_pkey_is_allocated(current->mm, pkey)) + ret = -EBADF; + up_write(¤t->mm->mmap_sem); + + if (ret) + return ret; + + ret = arch_get_user_pkey_access(current, pkey); + + return ret; +} + +SYSCALL_DEFINE3(pkey_set, int, pkey, unsigned long, access_rights, + unsigned long, flags) +{ + unsigned long ret = 0; + + if (flags) + return -EINVAL; + + down_write(¤t->mm->mmap_sem); + if (!mm_pkey_is_allocated(current->mm, pkey)) + ret = -EBADF; + up_write(¤t->mm->mmap_sem); + + if (ret) + return ret; + + ret = arch_set_user_pkey_access(current, pkey, access_rights); + + return ret; +} _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>