[PATCH] ARM: kprobes: Restrict probing SWP instructions to ARMv5 and below

[tixy@yxit.co.uk (Tixy)]

The SWP instruction is deprecated on ARMv6 and with ARMv7 it will be
UNDEFINED when CONFIG_SWP_EMULATE is selected. In this case, probing a
SWP instruction will cause an oops when the kprobes emulation code
executes an undefined instruction.

As the SWP instruction should be rare or non-existent in kernels for
ARMv6 and later, we can simply avoid these problems by not allowing
probing of these.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
---
 arch/arm/kernel/kprobes-arm.c      |    4 +++-
 arch/arm/kernel/kprobes-test-arm.c |   25 ++++++++++++++++---------
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/arch/arm/kernel/kprobes-arm.c b/arch/arm/kernel/kprobes-arm.c
index 9fe8910..8a30c89 100644
--- a/arch/arm/kernel/kprobes-arm.c
+++ b/arch/arm/kernel/kprobes-arm.c
@@ -519,10 +519,12 @@ static const union decode_item arm_cccc_0000_____1001_table[] = {
 static const union decode_item arm_cccc_0001_____1001_table[] = {
 	/* Synchronization primitives					*/
 
+#if __LINUX_ARM_ARCH__ < 6
+	/* Deprecated on ARMv6 and may be UNDEFINED on v7		*/
 	/* SMP/SWPB		cccc 0001 0x00 xxxx xxxx xxxx 1001 xxxx */
 	DECODE_EMULATEX	(0x0fb000f0, 0x01000090, emulate_rd12rn16rm0_rwflags_nopc,
 						 REGS(NOPC, NOPC, 0, 0, NOPC)),
-
+#endif
 	/* LDREX/STREX{,D,B,H}	cccc 0001 1xxx xxxx xxxx xxxx 1001 xxxx */
 	/* And unallocated instructions...				*/
 	DECODE_END
diff --git a/arch/arm/kernel/kprobes-test-arm.c b/arch/arm/kernel/kprobes-test-arm.c
index edf9ad8..ba32b39 100644
--- a/arch/arm/kernel/kprobes-test-arm.c
+++ b/arch/arm/kernel/kprobes-test-arm.c
@@ -427,18 +427,25 @@ void kprobe_arm_test_cases(void)
 
 	TEST_GROUP("Synchronization primitives")
 
-	/*
-	 * Use hard coded constants for SWP instructions to avoid warnings
-	 * about deprecated instructions.
-	 */
-	TEST_RP( ".word 0xe108e097 @ swp	lr, r",7,VAL2,", [r",8,0,"]")
-	TEST_R(  ".word 0x610d0091 @ swpvs	r0, r",1,VAL1,", [sp]")
-	TEST_RP( ".word 0xe10cd09e @ swp	sp, r",14,VAL2,", [r",12,13*4,"]")
+#if __LINUX_ARM_ARCH__ < 6
+	TEST_RP("swp	lr, r",7,VAL2,", [r",8,0,"]")
+	TEST_R( "swpvs	r0, r",1,VAL1,", [sp]")
+	TEST_RP("swp	sp, r",14,VAL2,", [r",12,13*4,"]")
+#else
+	TEST_UNSUPPORTED(".word 0xe108e097 @ swp	lr, r7, [r8]")
+	TEST_UNSUPPORTED(".word 0x610d0091 @ swpvs	r0, r1, [sp]")
+	TEST_UNSUPPORTED(".word 0xe10cd09e @ swp	sp, r14 [r12]")
+#endif
 	TEST_UNSUPPORTED(".word 0xe102f091 @ swp pc, r1, [r2]")
 	TEST_UNSUPPORTED(".word 0xe102009f @ swp r0, pc, [r2]")
 	TEST_UNSUPPORTED(".word 0xe10f0091 @ swp r0, r1, [pc]")
-	TEST_RP( ".word 0xe148e097 @ swpb	lr, r",7,VAL2,", [r",8,0,"]")
-	TEST_R(  ".word 0x614d0091 @ swpvsb	r0, r",1,VAL1,", [sp]")
+#if __LINUX_ARM_ARCH__ < 6
+	TEST_RP("swpb	lr, r",7,VAL2,", [r",8,0,"]")
+	TEST_R( "swpvsb	r0, r",1,VAL1,", [sp]")
+#else
+	TEST_UNSUPPORTED(".word 0xe148e097 @ swpb	lr, r7, [r8]")
+	TEST_UNSUPPORTED(".word 0x614d0091 @ swpvsb	r0, r1, [sp]")
+#endif
 	TEST_UNSUPPORTED(".word 0xe142f091 @ swpb pc, r1, [r2]")
 
 	TEST_UNSUPPORTED(".word	0xe1100090") /* Unallocated space */
-- 
1.7.2.5