x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation

mainline inclusion
from mainline-5.1
commit 6ae865615fc4
category: bugfix
bugzilla: 14433
CVE: NA

-------------------------------------------------

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: NRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Acked-by: NLinus 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.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>
Signed-off-by: NHongbo Yao <yaohongbo@huawei.com>
----
[conflicts]
	arch/x86/include/asm/uaccess.h
Reviewed-by: NXuefeng Wang <wxf.wang@hisilicon.com>
Reviewed-by: NChen Zhou <chenzhou10@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/x86/include/asm/uaccess.h

@@ -436,10 +436,11 @@ do {									\
 #define __put_user_nocheck(x, ptr, size)			\
 ({								\
 	int __pu_err;						\
-	__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_err, -EFAULT);\
+	__put_user_size(__pu_val, __pu_ptr, __pu_size, __pu_err, -EFAULT);\
 	__uaccess_end();					\
 	__builtin_expect(__pu_err, 0);				\
 })