ARM: kprobes: Fix emulation of LDRH, STRH, LDRSB and LDRSH instructions

The decoding of these instructions got the register indexed and
immediate indexed forms the wrong way around, causing incorrect
emulation.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/arm/kernel/kprobes-decode.c b/arch/arm/kernel/kprobes-decode.c
index c24e21ec427f..348ff47acd06 100644
--- a/arch/arm/kernel/kprobes-decode.c
+++ b/arch/arm/kernel/kprobes-decode.c
@@ -883,11 +883,12 @@ emulate_alu_tests(struct kprobe *p, struct pt_regs *regs)
 static enum kprobe_insn __kprobes
 prep_emulate_ldr_str(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 {
-        int ibit = (insn & (1 << 26)) ? 25 : 22;
+        int not_imm = (insn & (1 << 26)) ? (insn & (1 << 25))
+                                         : (~insn & (1 << 22));
 
         insn &= 0xfff00fff;
         insn |= 0x00001000;     /* Rn = r0, Rd = r1 */
-        if (insn & (1 << ibit)) {
+        if (not_imm) {
                 insn &= ~0xf;
                 insn |= 2;      /* Rm = r2 */
         }