From 58ab9a088ddac4efe823471275859d64f735577e Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Thu, 23 Feb 2017 14:26:03 -0800 Subject: [PATCH] x86/pkeys: Check against max pkey to avoid overflows Kirill reported a warning from UBSAN about undefined behavior when using protection keys. He is running on hardware that actually has support for it, which is not widely available. The warning triggers because of very large shifts of integers when doing a pkey_free() of a large, invalid value. This happens because we never check that the pkey "fits" into the mm_pkey_allocation_map(). I do not believe there is any danger here of anything bad happening other than some aliasing issues where somebody could do: pkey_free(35); and the kernel would effectively execute: pkey_free(8); While this might be confusing to an app that was doing something stupid, it has to do something stupid and the effects are limited to the app shooting itself in the foot. Signed-off-by: Dave Hansen Cc: stable@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Cc: shuah@kernel.org Cc: kirill.shutemov@linux.intel.com Link: http://lkml.kernel.org/r/20170223222603.A022ED65@viggo.jf.intel.com Signed-off-by: Thomas Gleixner --- arch/x86/include/asm/pkeys.h | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h index 34684adb6899..b3b09b98896d 100644 --- a/arch/x86/include/asm/pkeys.h +++ b/arch/x86/include/asm/pkeys.h @@ -46,6 +46,15 @@ extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey, static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) { + /* + * "Allocated" pkeys are those that have been returned + * from pkey_alloc(). pkey 0 is special, and never + * returned from pkey_alloc(). + */ + if (pkey <= 0) + return false; + if (pkey >= arch_max_pkey()) + return false; return mm_pkey_allocation_map(mm) & (1U << pkey); } @@ -82,12 +91,6 @@ int mm_pkey_alloc(struct mm_struct *mm) static inline int mm_pkey_free(struct mm_struct *mm, int pkey) { - /* - * pkey 0 is special, always allocated and can never - * be freed. - */ - if (!pkey) - return -EINVAL; if (!mm_pkey_is_allocated(mm, pkey)) return -EINVAL;