x86/uaccess: Don't leak the AC flag into __put_user() value evaluation

commit 2a418cf3f5f1caf911af288e978d61c9844b0695 upstream.

When calling __put_user(foo(), ptr), the __put_user() macro would call
foo() in between __uaccess_begin() and __uaccess_end().  If that code
were buggy, then those bugs would be run without SMAP protection.

Fortunately, there seem to be few instances of the problem in the
kernel. Nevertheless, __put_user() should be fixed to avoid doing this.
Therefore, evaluate __put_user()'s argument before setting AC.

This issue was noticed when an objtool hack by Peter Zijlstra complained
about genregs_get() and I compared the assembly output to the C source.

 [ bp: Massage commit message and fixed up whitespace. ]

Fixes: 11f1a4b9755f ("x86: reorganize SMAP handling in user space accesses")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20190225125231.845656645@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index aae77eb..4111edb 100644 (file)
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -293,8 +293,7 @@ do {                                                                        \
                __put_user_asm(x, ptr, retval, "l", "k", "ir", errret); \
                break;                                                  \
        case 8:                                                         \
-               __put_user_asm_u64((__typeof__(*ptr))(x), ptr, retval,  \
-                                  errret);                             \
+               __put_user_asm_u64(x, ptr, retval, errret);             \
                break;                                                  \
        default:                                                        \
                __put_user_bad();                                       \
@@ -440,8 +439,10 @@ do {                                                                       \
 #define __put_user_nocheck(x, ptr, size)                       \
 ({                                                             \
        int __pu_err;                                           \
+       __typeof__(*(ptr)) __pu_val;                            \
+       __pu_val = x;                                           \
        __uaccess_begin();                                      \
-       __put_user_size((x), (ptr), (size), __pu_err, -EFAULT); \
+       __put_user_size(__pu_val, (ptr), (size), __pu_err, -EFAULT);\
        __uaccess_end();                                        \
        __builtin_expect(__pu_err, 0);                          \
 })