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, 16 insertions, 0 deletions

diff --git a/arch/arm/kernel/kprobes-thumb.c b/arch/arm/kernel/kprobes-thumb.c
index 24a188b1601..973c3eb1243 100644
--- a/arch/arm/kernel/kprobes-thumb.c
+++ b/arch/arm/kernel/kprobes-thumb.c
@@ -33,9 +33,24 @@ static unsigned long __kprobes thumb_check_cc(unsigned long cpsr)
 	return true;
 }
 
+static void __kprobes thumb16_singlestep(struct kprobe *p, struct pt_regs *regs)
+{
+	regs->ARM_pc += 2;
+	p->ainsn.insn_handler(p, regs);
+	regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
+}
+
+static void __kprobes thumb32_singlestep(struct kprobe *p, struct pt_regs *regs)
+{
+	regs->ARM_pc += 4;
+	p->ainsn.insn_handler(p, regs);
+	regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
+}
+
 enum kprobe_insn __kprobes
 thumb16_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 {
+	asi->insn_singlestep = thumb16_singlestep;
 	asi->insn_check_cc = thumb_check_cc;
 	return INSN_REJECTED;
 }
@@ -43,6 +58,7 @@ thumb16_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 enum kprobe_insn __kprobes
 thumb32_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 {
+	asi->insn_singlestep = thumb32_singlestep;
 	asi->insn_check_cc = thumb_check_cc;
 	return INSN_REJECTED;
 }