Messages in this thread Patch in this message | | | Subject | [PATCH] x86/pkeys: add check for pkey "overflow" | From | Dave Hansen <> | Date | Wed, 22 Jan 2020 08:53:46 -0800 |
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Alex Shi reported the pkey macros above arch_set_user_pkey_access() to be unused. They are unused, and even refer to a nonexistent CONFIG option.
But, they might have served a good use, which was to ensure that the code does not try to set values that would not fit in the PKRU register. As it stands, a too-large 'pkey' value would be likely to silently overflow the u32 new_pkru_bits.
Add a check to look for overflows. Also add a comment to remind any future developer to closely examine the types used to store pkey values if arch_max_pkey() ever changes.
This boots and passes the x86 pkey selftests.
Reported-by: Alex Shi <alex.shi@linux.alibaba.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: x86@kernel.org Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Cyrill Gorcunov <gorcunov@gmail.com> Cc: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com> Cc: Aubrey Li <aubrey.li@linux.intel.com> Cc: linux-kernel@vger.kernel.org Signed-off-by: Dave Hansen <dave.hansen@intel.com> ---
b/arch/x86/include/asm/pkeys.h | 5 +++++ b/arch/x86/kernel/fpu/xstate.c | 9 +++++++-- 2 files changed, 12 insertions(+), 2 deletions(-)
diff -puN arch/x86/kernel/fpu/xstate.c~pkey-check-pkru-shift arch/x86/kernel/fpu/xstate.c --- a/arch/x86/kernel/fpu/xstate.c~pkey-check-pkru-shift 2020-01-21 09:20:26.542385466 -0800 +++ b/arch/x86/kernel/fpu/xstate.c 2020-01-21 09:28:18.068384290 -0800 @@ -902,8 +902,6 @@ const void *get_xsave_field_ptr(int xfea #ifdef CONFIG_ARCH_HAS_PKEYS -#define NR_VALID_PKRU_BITS (CONFIG_NR_PROTECTION_KEYS * 2) -#define PKRU_VALID_MASK (NR_VALID_PKRU_BITS - 1) /* * This will go out and modify PKRU register to set the access * rights for @pkey to @init_val. @@ -922,6 +920,13 @@ int arch_set_user_pkey_access(struct tas if (!boot_cpu_has(X86_FEATURE_OSPKE)) return -EINVAL; + /* + * This code should only be called with valid 'pkey' + * values originating from in-kernel users. Complain + * if a bad value is observed. + */ + WARN_ON_ONCE(pkey >= arch_max_pkey()); + /* Set the bits we need in PKRU: */ if (init_val & PKEY_DISABLE_ACCESS) new_pkru_bits |= PKRU_AD_BIT; diff -puN arch/x86/include/asm/pkeys.h~pkey-check-pkru-shift arch/x86/include/asm/pkeys.h --- a/arch/x86/include/asm/pkeys.h~pkey-check-pkru-shift 2020-01-21 09:23:36.733384991 -0800 +++ b/arch/x86/include/asm/pkeys.h 2020-01-21 09:41:44.797382278 -0800 @@ -4,6 +4,11 @@ #define ARCH_DEFAULT_PKEY 0 +/* + * If more than 16 keys are ever supported, a thorough audit + * will be necessary to ensure that the types that store key + * numbers and masks have sufficient capacity. + */ #define arch_max_pkey() (boot_cpu_has(X86_FEATURE_OSPKE) ? 16 : 1) extern int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, _
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