[PATCH AUTOSEL 4.19 158/209] s390/kasan: avoid user access code instrumentation

[Sasha Levin]

From: Vasily Gorbik <gor@xxxxxxxxxxxxx>

[ Upstream commit b6cbe3e8bdff6f21f1b58b08a55f479cdcf98282 ]

Kasan instrumentation adds "store" check for variables marked as
modified by inline assembly. With user pointers containing addresses
from another address space this produces false positives.

static inline unsigned long clear_user_xc(void __user *to, ...)
{
	asm volatile(
	...
	: "+a" (to) ...

User space access functions are wrapped by manually instrumented
functions in kasan common code, which should be sufficient to catch
errors. So, we just disable uaccess.o instrumentation altogether.

Reviewed-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/s390/lib/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/s390/lib/Makefile b/arch/s390/lib/Makefile
index 57ab40188d4bd..5418d10dc2a81 100644
--- a/arch/s390/lib/Makefile
+++ b/arch/s390/lib/Makefile
@@ -9,5 +9,9 @@ lib-$(CONFIG_SMP) += spinlock.o
 lib-$(CONFIG_KPROBES) += probes.o
 lib-$(CONFIG_UPROBES) += probes.o
 
+# Instrumenting memory accesses to __user data (in different address space)
+# produce false positives
+KASAN_SANITIZE_uaccess.o := n
+
 chkbss := mem.o
 include $(srctree)/arch/s390/scripts/Makefile.chkbss
-- 
2.20.1