x86/kasan: instrument user memory access API
Exchange between user and kernel memory is coded in assembly language.
Which means that such accesses won't be spotted by KASAN as a compiler
instruments only C code.
Add explicit KASAN checks to user memory access API to ensure that
userspace writes to (or reads from) a valid kernel memory.
Note: Unlike others strncpy_from_user() is written mostly in C and KASAN
sees memory accesses in it. However, it makes sense to add explicit
check for all @count bytes that *potentially* could be written to the
kernel.
[aryabinin@virtuozzo.com: move kasan check under the condition]
Link: http://lkml.kernel.org/r/1462869209-21096-1-git-send-email-aryabinin@virtuozzo.com
Link: http://lkml.kernel.org/r/1462538722-1574-4-git-send-email-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index 3384032..33f655e 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -1,5 +1,6 @@
#include <linux/compiler.h>
#include <linux/export.h>
+#include <linux/kasan-checks.h>
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/errno.h>
@@ -109,6 +110,7 @@
unsigned long max = max_addr - src_addr;
long retval;
+ kasan_check_write(dst, count);
user_access_begin();
retval = do_strncpy_from_user(dst, src, count, max);
user_access_end();