Messages in this thread Patch in this message | | | Subject | [PATCH ftrace/core v6 1/5] kprobes/ftrace: Recover original IP if pre_handler doesn't change it | From | Masami Hiramatsu <> | Date | Fri, 21 Nov 2014 05:25:09 -0500 |
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Recover original IP register if the pre_handler doesn't change it. Since current kprobes doesn't expect that another ftrace handler may change regs->ip, it sets kprobe.addr + MCOUNT_INSN_SIZE to regs->ip and returns to ftrace. This seems wrong behavior since kprobes can recover regs->ip and safely pass it to another handler.
This adds a code which recovers original regs->ip passed from ftrace right before returning to ftrace, so that another ftrace user can change regs->ip.
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
--- Changes in v4: - Fix description and remove bugfix tag. --- arch/x86/kernel/kprobes/ftrace.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c index 717b02a..5f8f0b3 100644 --- a/arch/x86/kernel/kprobes/ftrace.c +++ b/arch/x86/kernel/kprobes/ftrace.c @@ -27,7 +27,7 @@ static nokprobe_inline int __skip_singlestep(struct kprobe *p, struct pt_regs *regs, - struct kprobe_ctlblk *kcb) + struct kprobe_ctlblk *kcb, unsigned long orig_ip) { /* * Emulate singlestep (and also recover regs->ip) @@ -39,6 +39,8 @@ int __skip_singlestep(struct kprobe *p, struct pt_regs *regs, p->post_handler(p, regs, 0); } __this_cpu_write(current_kprobe, NULL); + if (orig_ip) + regs->ip = orig_ip; return 1; } @@ -46,7 +48,7 @@ int skip_singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { if (kprobe_ftrace(p)) - return __skip_singlestep(p, regs, kcb); + return __skip_singlestep(p, regs, kcb, 0); else return 0; } @@ -71,13 +73,14 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, if (kprobe_running()) { kprobes_inc_nmissed_count(p); } else { + unsigned long orig_ip = regs->ip; /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */ regs->ip = ip + sizeof(kprobe_opcode_t); __this_cpu_write(current_kprobe, p); kcb->kprobe_status = KPROBE_HIT_ACTIVE; if (!p->pre_handler || !p->pre_handler(p, regs)) - __skip_singlestep(p, regs, kcb); + __skip_singlestep(p, regs, kcb, orig_ip); /* * If pre_handler returns !0, it sets regs->ip and * resets current kprobe.
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