[PATCH] kprobes: only test 'sub pc, pc, #1b-2b+8-2' on ARMv6

[Rabin Vincent]

On Wed, Jun 13, 2012 at 12:48 PM, Tixy <tixy at yxit.co.uk> wrote:
> I agree with this analysis. However, it is possible to have a kernel
> built to support both ARM v6 and v7 (e.g OMAP2+) in which case
> __LINUX_ARM_ARCH__ == 6 will be true but the code could be running on v7
> hardware. Therefore a compile time check for ARM architecture isn't
> sufficient to fix the problem.

How about the following check instead?  At least one other place uses
it.

8<---
>From f1e1794c0c12e39e99d4169c934fd43feb889d7b Mon Sep 17 00:00:00 2001
From: Rabin Vincent <rabin.vincent at stericsson.com>
Date: Mon, 11 Jun 2012 16:55:37 +0530
Subject: [PATCH] ARM: kprobes: only test 'sub pc, pc, #1b-2b+8-2' on ARMv6

'sub pc, pc, #1b-2b+8-2' results in address<1:0> == '10'.

sub pc, pc, #const (== ADR pc, #const) performs an interworking branch
(BXWritePC()) on ARMv7+ and a simple branch (BranchWritePC()) on earlier
versions.

In ARM state, BXWritePC() is UNPREDICTABLE when address<1:0> == '10'.

In ARM state on ARMv6+, BranchWritePC() ignores address<1:0>.  Before
ARMv6, BranchWritePC() is UNPREDICTABLE if address<1:0> != '00'

So the instruction is UNPREDICTABLE both before and after v6.

Signed-off-by: Rabin Vincent <rabin.vincent at stericsson.com>
---
 arch/arm/kernel/kprobes-test-arm.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/kprobes-test-arm.c
b/arch/arm/kernel/kprobes-test-arm.c
index ba32b39..38c1a3b 100644
--- a/arch/arm/kernel/kprobes-test-arm.c
+++ b/arch/arm/kernel/kprobes-test-arm.c
@@ -187,8 +187,8 @@ void kprobe_arm_test_cases(void)
 	TEST_BF_R ("mov	pc, r",0,2f,"")
 	TEST_BF_RR("mov	pc, r",0,2f,", asl r",1,0,"")
 	TEST_BB(   "sub	pc, pc, #1b-2b+8")
-#if __LINUX_ARM_ARCH__ >= 6
-	TEST_BB(   "sub	pc, pc, #1b-2b+8-2") /* UNPREDICTABLE before ARMv6 */
+#if __LINUX_ARM_ARCH__ == 6 && !defined(CONFIG_CPU_V7)
+	TEST_BB(   "sub	pc, pc, #1b-2b+8-2") /* UNPREDICTABLE before and
after ARMv6 */
 #endif
 	TEST_BB_R( "sub	pc, pc, r",14, 1f-2f+8,"")
 	TEST_BB_R( "rsb	pc, r",14,1f-2f+8,", pc")
-- 
1.7.9.5