ARM: kprobes: Add hooks to override singlestep()

When a probe fires we must single-step the instruction which was
replaced by a breakpoint. As the steps to do this vary between ARM and
Thumb instructions we need a way to customise single-stepping.

This is done by adding a new hook called insn_singlestep to
arch_specific_insn which is initialised by the instruction decoding
functions.

These single-step hooks must update PC and call the instruction handler.
For Thumb instructions an additional step of updating ITSTATE is needed.
We do this after calling the handler because some handlers will need to
test if they are running in an IT block.

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

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/arm/kernel/kprobes-arm.c b/arch/arm/kernel/kprobes-arm.c
index 0262b29163d1..a1143e86a09a 100644
--- a/arch/arm/kernel/kprobes-arm.c
+++ b/arch/arm/kernel/kprobes-arm.c
@@ -1494,6 +1494,12 @@ space_cccc_11xx(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 	return INSN_REJECTED;
 }
 
+static void __kprobes arm_singlestep(struct kprobe *p, struct pt_regs *regs)
+{
+	regs->ARM_pc += 4;
+	p->ainsn.insn_handler(p, regs);
+}
+
 /* Return:
  *   INSN_REJECTED     If instruction is one not allowed to kprobe,
  *   INSN_GOOD         If instruction is supported and uses instruction slot,
@@ -1509,6 +1515,7 @@ space_cccc_11xx(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 enum kprobe_insn __kprobes
 arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 {
+	asi->insn_singlestep = arm_singlestep;
 	asi->insn_check_cc = kprobe_condition_checks[insn>>28];
 	asi->insn[1] = KPROBE_RETURN_INSTRUCTION;