[PATCH 3.16 156/212] s390/chsc: Add exception handler for CHSC instruction

[Ben Hutchings]

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Oberparleiter <oberpar@xxxxxxxxxxxxxxxxxx>

commit 77759137248f34864a8f7a58bbcebfcf1047504a upstream.

Prevent kernel crashes due to unhandled exceptions raised by the CHSC
instruction which may for example be triggered by invalid ioctl data.

Fixes: 64150adf89df ("s390/cio: Introduce generic synchronous CHSC IOCTL")
Signed-off-by: Peter Oberparleiter <oberpar@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Sebastian Ott <sebott@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/s390/cio/ioasm.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/s390/cio/ioasm.h
+++ b/drivers/s390/cio/ioasm.h
@@ -138,13 +138,15 @@ static inline int tpi(struct tpi_info *a
 static inline int chsc(void *chsc_area)
 {
 	typedef struct { char _[4096]; } addr_type;
-	int cc;
+	int cc = -EIO;
 
 	asm volatile(
 		"	.insn	rre,0xb25f0000,%2,0\n"
-		"	ipm	%0\n"
+		"0:	ipm	%0\n"
 		"	srl	%0,28\n"
-		: "=d" (cc), "=m" (*(addr_type *) chsc_area)
+		"1:\n"
+		EX_TABLE(0b, 1b)
+		: "+d" (cc), "=m" (*(addr_type *) chsc_area)
 		: "d" (chsc_area), "m" (*(addr_type *) chsc_area)
 		: "cc");
 	return cc;