From 6ae865615fc43d014da2fd1f1bba7e81ee622d1b Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 24 Apr 2019 09:19:24 +0200 Subject: x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation The __put_user() macro evaluates it's @ptr argument inside the __uaccess_begin() / __uaccess_end() region. While this would normally not be expected to be an issue, an UBSAN bug (it ignored -fwrapv, fixed in GCC 8+) would transform the @ptr evaluation for: drivers/gpu/drm/i915/i915_gem_execbuffer.c: if (unlikely(__put_user(offset, &urelocs[r-stack].presumed_offset))) { into a signed-overflow-UB check and trigger the objtool AC validation. Finish this commit: 2a418cf3f5f1 ("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") and explicitly evaluate all 3 arguments early. Reported-by: Randy Dunlap Signed-off-by: Peter Zijlstra (Intel) Acked-by: Randy Dunlap # build-tested Acked-by: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: luto@kernel.org Fixes: 2a418cf3f5f1 ("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") Link: http://lkml.kernel.org/r/20190424072208.695962771@infradead.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/uaccess.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 5ca7b91faf67..bb21913885a3 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -427,10 +427,11 @@ do { \ ({ \ __label__ __pu_label; \ int __pu_err = -EFAULT; \ - __typeof__(*(ptr)) __pu_val; \ - __pu_val = x; \ + __typeof__(*(ptr)) __pu_val = (x); \ + __typeof__(ptr) __pu_ptr = (ptr); \ + __typeof__(size) __pu_size = (size); \ __uaccess_begin(); \ - __put_user_size(__pu_val, (ptr), (size), __pu_label); \ + __put_user_size(__pu_val, __pu_ptr, __pu_size, __pu_label); \ __pu_err = 0; \ __pu_label: \ __uaccess_end(); \ -- cgit v1.2.3-59-g8ed1b