Commit 06961928 authored Aug 29, 2019 by Peter Zijlstra Committed by Greg Kroah-Hartman Sep 21, 2019

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>

parent ab1dfea6

arch/x86/include/asm/uaccess.h

+3 −1

Original line number	Diff line number	Diff line
		@@ -438,8 +438,10 @@ 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); \