powerpc/64: Use barrier_nospec in syscall entry

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>

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 3d1af55..b10e010 100644 (file)
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -36,6 +36,7 @@
 #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>
@@ -178,6 +179,15 @@ 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 */