[PATCH] powerpc/kprobes: fix singlestep out-of-line

We currently single-step inline if the instruction on which a kprobe is
inserted is a trap variant.

- variants (such as tdnei, used by BUG()) typically evaluate a condition
  and cause a trap only if the condition is satisfied.
- kprobes uses the unconditional "trap" (0x7fe00008) and single-stepping
  again on this instruction, resulting in another trap without
  evaluating the condition is obviously incorrect.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 856ef1a..f788663 100644 (file)
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -90,15 +90,15 @@ void __kprobes arch_remove_kprobe(struct kprobe *p)
 
 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
-       kprobe_opcode_t insn = *p->ainsn.insn;
-
        regs->msr |= MSR_SE;
 
-       /* single step inline if it is a trap variant */
-       if (is_trap(insn))
-               regs->nip = (unsigned long)p->addr;
-       else
-               regs->nip = (unsigned long)p->ainsn.insn;
+       /*
+        * On powerpc we should single step on the original
+        * instruction even if the probed insn is a trap
+        * variant as values in regs could play a part in
+        * if the trap is taken or not
+        */
+       regs->nip = (unsigned long)p->ainsn.insn;
 }
 
 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)