ARM: 7181/1: Restrict kprobes probing SWP instructions to ARMv5 and below

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.

Reported-by: Leif Lindholm <leif.lindholm@arm.com>
Tested-by: Leif Lindholm <leif.lindholm@arm.com>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

2 files changed, 19 insertions, 10 deletions

diff --git a/arch/arm/kernel/kprobes-arm.c b/arch/arm/kernel/kprobes-arm.c
index 9fe8910308af..8a30c89da70e 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 edf9ad8d3c6b..ba32b393b3f0 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 */