x86/uaccess: Don't leak the AC flags into __get_user() argument evaluation

[ Upstream commit 9b8bd476e78e89c9ea26c3b435ad0201c3d7dbf5 ]

Identical to __put_user(); the __get_user() argument evalution will too
leak UBSAN crud into the __uaccess_begin() / __uaccess_end() region.
While uncommon this was observed to happen for:

  drivers/xen/gntdev.c: if (__get_user(old_status, batch->status[i]))

where UBSAN added array bound checking.

This complements commit:

  6ae865615fc4 ("x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation")

Tested-by Sedat Dilek <sedat.dilek@gmail.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: broonie@kernel.org
Cc: sfr@canb.auug.org.au
Cc: akpm@linux-foundation.org
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: mhocko@suse.cz
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20190829082445.GM2369@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 4111edb..9718303 100644 (file)
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -451,8 +451,10 @@ do {                                                                       \
 ({                                                                     \
        int __gu_err;                                                   \
        __inttype(*(ptr)) __gu_val;                                     \
+       __typeof__(ptr) __gu_ptr = (ptr);                               \
+       __typeof__(size) __gu_size = (size);                            \
        __uaccess_begin_nospec();                                       \
-       __get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT);    \
+       __get_user_size(__gu_val, __gu_ptr, __gu_size, __gu_err, -EFAULT);      \
        __uaccess_end();                                                \
        (x) = (__force __typeof__(*(ptr)))__gu_val;                     \
        __builtin_expect(__gu_err, 0);                                  \