In trap-based (classic) kprobes, we try to emulate the probed
instruction so as to avoid having to single step it. We use a flag to
determine if the probed instruction was successfully emulated, so that we
can speed up subsequent probe hits.
However, emulate_step() doesn't differentiate between unknown
instructions and an emulation attempt that failed. As such, the current
heuristic is not of much use. Instead, use analyse_instr() during kprobe
registration to determine if the probed instruction can be decoded by
our instruction emulation infrastructure. For unknown instructions, we
can then directly single-step while for other instructions, we can
attempt to emulate and fall back to single stepping if that fails.
Signed-off-by: Naveen N. Rao <redacted>
---
arch/powerpc/kernel/kprobes.c | 62 +++++++++--------------------------
1 file changed, 16 insertions(+), 46 deletions(-)
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index b7b20875d34d91..bbef9e918ecb39 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -107,6 +107,8 @@ int arch_prepare_kprobe(struct kprobe *p)
{
int ret = 0;
struct kprobe *prev;
+ struct pt_regs regs;
+ struct instruction_op op;
struct ppc_inst insn = ppc_inst_read((struct ppc_inst *)p->addr);
if ((unsigned long)p->addr & 0x03) {@@ -140,9 +142,18 @@ int arch_prepare_kprobe(struct kprobe *p)
if (!ret) {
patch_instruction((struct ppc_inst *)p->ainsn.insn, insn);
p->opcode = ppc_inst_val(insn);
+
+ /* Check if this is an instruction we recognise */
+ p->ainsn.boostable = 0;
+ memset(®s, 0, sizeof(struct pt_regs));
+ regs.nip = (unsigned long)p->addr;
+ regs.msr = MSR_KERNEL;
+ ret = analyse_instr(&op, ®s, insn);
+ if (ret == 1 || (ret == 0 && GETTYPE(op.type) != UNKNOWN))
+ p->ainsn.boostable = 1;
+ ret = 0;
}
- p->ainsn.boostable = 0;
return ret;
}
NOKPROBE_SYMBOL(arch_prepare_kprobe);@@ -225,47 +236,6 @@ void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
}
NOKPROBE_SYMBOL(arch_prepare_kretprobe);
-static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
-{
- int ret;
- struct ppc_inst insn = ppc_inst_read((struct ppc_inst *)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 %s\n", ppc_inst_as_str(insn));
- BUG();
- } else {
- /*
- * If we haven't previously emulated this instruction, then it
- * can't be boosted. Note it down so we don't try to do so again.
- *
- * If, however, we had emulated this instruction in the past,
- * then this is just an error with the current run (for
- * instance, exceptions due to a load/store). We return 0 so
- * that this is now single-stepped, but continue to try
- * emulating it in subsequent probe hits.
- */
- if (unlikely(p->ainsn.boostable != 1))
- p->ainsn.boostable = -1;
- }
-
- return ret;
-}
-NOKPROBE_SYMBOL(try_to_emulate);
-
int kprobe_handler(struct pt_regs *regs)
{
struct kprobe *p;@@ -334,8 +304,8 @@ int kprobe_handler(struct pt_regs *regs)
set_current_kprobe(p, regs, kcb);
kprobes_inc_nmissed_count(p);
kcb->kprobe_status = KPROBE_REENTER;
- if (p->ainsn.boostable >= 0) {
- ret = try_to_emulate(p, regs);
+ if (p->ainsn.boostable) {
+ ret = emulate_step(regs, ppc_inst_read((struct ppc_inst *)p->ainsn.insn));
if (ret > 0) {
restore_previous_kprobe(kcb);@@ -356,8 +326,8 @@ int kprobe_handler(struct pt_regs *regs)
return 1;
}
- if (p->ainsn.boostable >= 0) {
- ret = try_to_emulate(p, regs);
+ if (p->ainsn.boostable) {
+ ret = emulate_step(regs, ppc_inst_read((struct ppc_inst *)p->ainsn.insn));
if (ret > 0) {
if (p->post_handler)--
2.30.2