[PATCH 14/25] x86/uaccess,ubsan: Fix UBSAN vs SMAP

[Peter Zijlstra <peterz@infradead.org>]

UBSAN can insert extra code in random locations; including AC=1
sections. Typically this code is not safe and needs wrapping.

So far, only __ubsan_handle_type_mismatch* have been observed in AC=1
sections and therefore only those are annotated.

Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 lib/Makefile |    1 +
 lib/ubsan.c  |    4 ++++
 2 files changed, 5 insertions(+)

--- a/lib/Makefile
+++ b/lib/Makefile
@@ -263,6 +263,7 @@ obj-$(CONFIG_UCS2_STRING) += ucs2_string
 obj-$(CONFIG_UBSAN) += ubsan.o
 
 UBSAN_SANITIZE_ubsan.o := n
+CFLAGS_ubsan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
 obj-$(CONFIG_SBITMAP) += sbitmap.o
 
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -17,6 +17,7 @@
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/sched.h>
+#include <linux/uaccess.h>
 
 #include "ubsan.h"
 
@@ -313,6 +314,7 @@ static void handle_object_size_mismatch(
 static void ubsan_type_mismatch_common(struct type_mismatch_data_common *data,
 				unsigned long ptr)
 {
+	unsigned long flags = user_access_save();
 
 	if (!ptr)
 		handle_null_ptr_deref(data);
@@ -320,6 +322,8 @@ static void ubsan_type_mismatch_common(s
 		handle_misaligned_access(data, ptr);
 	else
 		handle_object_size_mismatch(data, ptr);
+
+	user_access_restore(flags);
 }
 
 void __ubsan_handle_type_mismatch(struct type_mismatch_data *data,