[PATCH stable v4.9 08/35] powerpc/64: Use barrier_nospec in syscall entry

Michael Ellerman
2019-04-11T11:46:47Z

commit 51973a815c6b46d7b23b68d6af371ad1c9d503ca upstream.

Our syscall entry is done in assembly so patch in an explicit
barrier_nospec.

Based on a patch by Michal Suchanek.

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
arch/powerpc/kernel/entry_64.S | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index e24ae0fa80ed..11e390662384 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -38,6 +38,7 @@
#include <asm/context_tracking.h>
#include <asm/tm.h>
#include <asm/ppc-opcode.h>
+#include <asm/barrier.h>
#include <asm/export.h>
#ifdef CONFIG_PPC_BOOK3S
#include <asm/exception-64s.h>
@@ -180,6 +181,15 @@ system_call: /* label this so stack traces look sane */
clrldi r8,r8,32
15:
slwi r0,r0,4
+
+ barrier_nospec_asm
+ /*
+ * Prevent the load of the handler below (based on the user-passed
+ * system call number) being speculatively executed until the test
+ * against NR_syscalls and branch to .Lsyscall_enosys above has
+ * committed.
+ */
+
ldx r12,r11,r0 /* Fetch system call handler [ptr] */
mtctr r12
bctrl /* Call handler */
--
2.20.1