Add user pointer masking to __put_user() to mitigate Spectre v1.
A write in a mispredicted access_ok() branch to a user-controlled kernel
address can populate the rest of the affected cache line with kernel
data.
This makes its behavior identical to put_user(), so converge their
implementations.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
arch/x86/lib/putuser.S | 27 ++++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)
diff --git a/arch/x86/lib/putuser.S b/arch/x86/lib/putuser.S
index cb137e0286be..1b122261b7aa 100644
--- a/arch/x86/lib/putuser.S
+++ b/arch/x86/lib/putuser.S
@@ -87,7 +87,26 @@ SYM_FUNC_START(__put_user_8)
SYM_FUNC_END(__put_user_8)
EXPORT_SYMBOL(__put_user_8)
-/* .. and the same for __put_user, just without the range checks */
+#ifdef CONFIG_X86_64
+
+/*
+ * On x86-64, put_user() does address masking rather than a conditional
+ * bounds check so there's no functional difference with __put_user().
+ */
+SYM_FUNC_ALIAS(__put_user_nocheck_1, __put_user_1);
+EXPORT_SYMBOL(__put_user_nocheck_1);
+
+SYM_FUNC_ALIAS(__put_user_nocheck_2, __put_user_2);
+EXPORT_SYMBOL(__put_user_nocheck_2);
+
+SYM_FUNC_ALIAS(__put_user_nocheck_4, __put_user_4);
+EXPORT_SYMBOL(__put_user_nocheck_4);
+
+SYM_FUNC_ALIAS(__put_user_nocheck_8, __put_user_8);
+EXPORT_SYMBOL(__put_user_nocheck_8);
+
+#else /* CONFIG_X86_32 */
+
SYM_FUNC_START(__put_user_nocheck_1)
ASM_STAC
6: movb %al,(%_ASM_CX)
@@ -118,15 +137,15 @@ EXPORT_SYMBOL(__put_user_nocheck_4)
SYM_FUNC_START(__put_user_nocheck_8)
ASM_STAC
9: mov %_ASM_AX,(%_ASM_CX)
-#ifdef CONFIG_X86_32
10: movl %edx,4(%_ASM_CX)
-#endif
xor %ecx,%ecx
ASM_CLAC
RET
SYM_FUNC_END(__put_user_nocheck_8)
EXPORT_SYMBOL(__put_user_nocheck_8)
+#endif /* CONFIG_X86_32 */
+
SYM_CODE_START_LOCAL(__put_user_handle_exception)
ASM_CLAC
.Lbad_put_user:
@@ -140,11 +159,9 @@ SYM_CODE_END(__put_user_handle_exception)
_ASM_EXTABLE_UA(4b, __put_user_handle_exception)
#ifdef CONFIG_X86_32
_ASM_EXTABLE_UA(5b, __put_user_handle_exception)
-#endif
_ASM_EXTABLE_UA(6b, __put_user_handle_exception)
_ASM_EXTABLE_UA(7b, __put_user_handle_exception)
_ASM_EXTABLE_UA(8b, __put_user_handle_exception)
_ASM_EXTABLE_UA(9b, __put_user_handle_exception)
-#ifdef CONFIG_X86_32
_ASM_EXTABLE_UA(10b, __put_user_handle_exception)
#endif
--
2.47.0