[src/trunk]: src/sys/arch/aarch64 Add a speculation barrier after the 'eret'.

[ryo <ryo%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ad13b0b7d777
branches:  trunk
changeset: 1005774:ad13b0b7d777
user:      ryo <ryo%NetBSD.org@localhost>
date:      Fri Dec 20 07:16:43 2019 +0000

description:
Add a speculation barrier after the 'eret'.

Some aarch64 cpus speculatively execute instructions after 'eret',
and this potentiates side-channel attack.

from
 https://github.com/torvalds/linux/commit/679db70801da9fda91d26caf13bf5b5ccc74e8e8

diffstat:

 sys/arch/aarch64/aarch64/cpuswitch.S |   8 ++++----
 sys/arch/aarch64/include/asm.h       |  11 ++++++++++-
 2 files changed, 14 insertions(+), 5 deletions(-)

diffs (61 lines):

diff -r 93c3dbebeb8a -r ad13b0b7d777 sys/arch/aarch64/aarch64/cpuswitch.S
--- a/sys/arch/aarch64/aarch64/cpuswitch.S      Fri Dec 20 04:04:25 2019 +0000
+++ b/sys/arch/aarch64/aarch64/cpuswitch.S      Fri Dec 20 07:16:43 2019 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: cpuswitch.S,v 1.12 2019/09/15 07:13:37 skrll Exp $ */
+/* $NetBSD: cpuswitch.S,v 1.13 2019/12/20 07:16:43 ryo Exp $ */
 
 /*-
  * Copyright (c) 2014 The NetBSD Foundation, Inc.
@@ -37,7 +37,7 @@
 #include "opt_ddb.h"
 #include "opt_kasan.h"
 
-RCSID("$NetBSD: cpuswitch.S,v 1.12 2019/09/15 07:13:37 skrll Exp $")
+RCSID("$NetBSD: cpuswitch.S,v 1.13 2019/12/20 07:16:43 ryo Exp $")
 
 /*
  * At IPL_SCHED:
@@ -268,7 +268,7 @@
        ldp     x1, x2, [x0, #TF_X1]
        ldr     x0, [x0, #TF_X0]
 
-       eret
+       ERET
 END(el1_trap_exit)
 #ifdef DDB
 END(el1_trap)
@@ -339,7 +339,7 @@
        unwind_x0_x2
 
        /* leave sp at l_md.md_utf, return back to EL0 user process */
-       eret
+       ERET
 END(el0_trap_exit)
 #ifdef DDB
 END(el0_trap)
diff -r 93c3dbebeb8a -r ad13b0b7d777 sys/arch/aarch64/include/asm.h
--- a/sys/arch/aarch64/include/asm.h    Fri Dec 20 04:04:25 2019 +0000
+++ b/sys/arch/aarch64/include/asm.h    Fri Dec 20 07:16:43 2019 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: asm.h,v 1.4 2019/08/05 16:24:48 joerg Exp $ */
+/* $NetBSD: asm.h,v 1.5 2019/12/20 07:16:43 ryo Exp $ */
 
 #ifndef _AARCH64_ASM_H_
 #define _AARCH64_ASM_H_
@@ -8,6 +8,15 @@
 #ifdef __aarch64__
 #define        fp      x29
 #define        lr      x30
+
+/*
+ * Add a speculation barrier after the 'eret'.
+ * Some aarch64 cpus speculatively execute instructions after 'eret',
+ * and this potentiates side-channel attacks.
+ */
+#define        ERET    \
+       eret; dsb sy; isb
+
 #endif
 
 #endif /* !_AARCH64_ASM_H_ */