ARM: kprobes: enable OPTPROBES for ARM 32

This patch introduce kprobeopt for ARM 32.

Limitations:
 - Currently only kernel compiled with ARM ISA is supported.

 - Offset between probe point and optinsn slot must not larger than
   32MiB. Masami Hiramatsu suggests replacing 2 words, it will make
   things complex. Futher patch can make such optimization.

Kprobe opt on ARM is relatively simpler than kprobe opt on x86 because
ARM instruction is always 4 bytes aligned and 4 bytes long. This patch
replace probed instruction by a 'b', branch to trampoline code and then
calls optimized_callback(). optimized_callback() calls opt_pre_handler()
to execute kprobe handler. It also emulate/simulate replaced instruction.

When unregistering kprobe, the deferred manner of unoptimizer may leave
branch instruction before optimizer is called. Different from x86_64,
which only copy the probed insn after optprobe_template_end and
reexecute them, this patch call singlestep to emulate/simulate the insn
directly. Futher patch can optimize this behavior.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Jon Medhurst (Tixy) <tixy@linaro.org>
Signed-off-by: Jon Medhurst <tixy@linaro.org>

1 files changed, 19 insertions, 7 deletions

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index 3a58db4cc1c6..a4ec240ee7ba 100644
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -163,19 +163,31 @@ void __kprobes arch_arm_kprobe(struct kprobe *p)
  * memory. It is also needed to atomically set the two half-words of a 32-bit
  * Thumb breakpoint.
  */
-int __kprobes __arch_disarm_kprobe(void *p)
-{
-	struct kprobe *kp = p;
-	void *addr = (void *)((uintptr_t)kp->addr & ~1);
-
-	__patch_text(addr, kp->opcode);
+struct patch {
+	void *addr;
+	unsigned int insn;
+};
 
+static int __kprobes_remove_breakpoint(void *data)
+{
+	struct patch *p = data;
+	__patch_text(p->addr, p->insn);
 	return 0;
 }
 
+void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
+{
+	struct patch p = {
+		.addr = addr,
+		.insn = insn,
+	};
+	stop_machine(__kprobes_remove_breakpoint, &p, cpu_online_mask);
+}
+
 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 {
-	stop_machine(__arch_disarm_kprobe, p, cpu_online_mask);
+	kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
+			p->opcode);
 }
 
 void __kprobes arch_remove_kprobe(struct kprobe *p)