[PATCH 10/20] x86/uaccess,ubsan: Fix UBSAN vs SMAP

From: Peter Zijlstra
Date: Thu Mar 07 2019 - 06:53:10 EST


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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
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,