[PATCH 4.14 53/80] s390: do not bypass BPENTER for interrupt system calls

From: Greg Kroah-Hartman
Date: Fri Apr 27 2018 - 10:46:47 EST

4.14-stable review patch. If anyone has any objections, please let me know.


From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

[ Upstream commit d5feec04fe578c8dbd9e2e1439afc2f0af761ed4 ]

The system call path can be interrupted before the switch back to the
standard branch prediction with BPENTER has been done. The critical
section cleanup code skips forward to .Lsysc_do_svc and bypasses the
BPENTER. In this case the kernel and all subsequent code will run with
the limited branch prediction.

Fixes: eacf67eb9b32 ("s390: run user space and KVM guests with modified branch prediction")
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
arch/s390/kernel/entry.S | 1 +
1 file changed, 1 insertion(+)

--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -1375,6 +1375,7 @@ cleanup_critical:
stg %r15,__LC_SYSTEM_TIMER
0: # update accounting time stamp
+ BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
# set up saved register r11