| From e55d08b9118a4078334fb7f3218ae0ebcba12dba Mon Sep 17 00:00:00 2001 |
| From: Peter Zijlstra <peterz@infradead.org> |
| Date: Wed, 24 Apr 2019 09:19:24 +0200 |
| Subject: x86/uaccess: Dont leak the AC flag into __put_user() argument |
| evaluation |
| |
| [ Upstream commit 6ae865615fc43d014da2fd1f1bba7e81ee622d1b ] |
| |
| 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 <rdunlap@infradead.org> |
| Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> |
| Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested |
| Acked-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| 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 <mingo@kernel.org> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| 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 1954dd5552a2e..3822cc8ac9d6d 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(); \ |
| -- |
| 2.20.1 |
| |