[PATCH v2 4/5] powerpc: kprobes: factor out code to emulate instruction into a helper

Naveen N. Rao
2017-04-12T10:59:54Z

This helper will be used in a subsequent patch to emulate instructions
on re-entering the kprobe handler. No functional change.

Acked-by: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
arch/powerpc/kernel/kprobes.c | 52 ++++++++++++++++++++++++++-----------------
1 file changed, 31 insertions(+), 21 deletions(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 0732a0291ace..8b48f7d046bd 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -207,6 +207,35 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
regs->link = (unsigned long)kretprobe_trampoline;
}

+int __kprobes try_to_emulate(struct kprobe *p, struct pt_regs *regs)
+{
+ int ret;
+ unsigned int insn = *p->ainsn.insn;
+
+ /* regs->nip is also adjusted if emulate_step returns 1 */
+ ret = emulate_step(regs, insn);
+ if (ret > 0) {
+ /*
+ * Once this instruction has been boosted
+ * successfully, set the boostable flag
+ */
+ if (unlikely(p->ainsn.boostable == 0))
+ p->ainsn.boostable = 1;
+ } else if (ret < 0) {
+ /*
+ * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
+ * So, we should never get here... but, its still
+ * good to catch them, just in case...
+ */
+ printk("Can't step on instruction %x\n", insn);
+ BUG();
+ } else if (ret == 0)
+ /* This instruction can't be boosted */
+ p->ainsn.boostable = -1;
+
+ return ret;
+}
+
int __kprobes kprobe_handler(struct pt_regs *regs)
{
struct kprobe *p;
@@ -302,18 +331,9 @@ int __kprobes kprobe_handler(struct pt_regs *regs)

ss_probe:
if (p->ainsn.boostable >= 0) {
- unsigned int insn = *p->ainsn.insn;
+ ret = try_to_emulate(p, regs);

- /* regs->nip is also adjusted if emulate_step returns 1 */
- ret = emulate_step(regs, insn);
if (ret > 0) {
- /*
- * Once this instruction has been boosted
- * successfully, set the boostable flag
- */
- if (unlikely(p->ainsn.boostable == 0))
- p->ainsn.boostable = 1;
-
if (p->post_handler)
p->post_handler(p, regs, 0);

@@ -321,17 +341,7 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
reset_current_kprobe();
preempt_enable_no_resched();
return 1;
- } else if (ret < 0) {
- /*
- * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
- * So, we should never get here... but, its still
- * good to catch them, just in case...
- */
- printk("Can't step on instruction %x\n", insn);
- BUG();
- } else if (ret == 0)
- /* This instruction can't be boosted */
- p->ainsn.boostable = -1;
+ }
}
prepare_singlestep(p, regs);
kcb->kprobe_status = KPROBE_HIT_SS;
--
2.12.1