Re: [PATCH -tip 4/4] [BUGFIX] kprobes/x86: Fix to support jprobes on ftrace-based kprobe

Masami Hiramatsu
2012-09-07T08:44:31Z

(2012/09/05 23:31), Masami Hiramatsu wrote:
> Fix kprobes/x86 to support jprobes on ftrace-based kprobes.
> Because of -mfentry support of ftrace, ftrace is now put
> on the beginning of function where jprobes are put.
>
> Originally ftrace-based kprobes doesn't support jprobe
> because it will change regs->ip and ftrace doesn't support
> changing IP and ftrace itself doesn't conflict jprobe.
> However, ftrace -mfentry support moves mcount call on the
> top of functions where jprobes are put. This means that
> jprobe always conflicts with ftrace-based kprobe and fails.
>
> This patch allows ftrace-based kprobes to support jprobes
> by allowing to modify regs->ip and kprobes breakpoint
> handler also allows to skip singlestepping because there
> is a ftrace call (not an original instruction).
>
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>

This should have a below line...

Reported-by: Fengguang Wu <fengguang.wu@intel.com>

Thanks!

> ---
>
> arch/x86/kernel/kprobes.c | 42 +++++++++++++++++++++++++++++-------------
> kernel/kprobes.c | 3 ---
> 2 files changed, 29 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
> index f49f60c..b7c2a85 100644
> --- a/arch/x86/kernel/kprobes.c
> +++ b/arch/x86/kernel/kprobes.c
> @@ -541,6 +541,8 @@ reenter_kprobe(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb
> return 1;
> }
>
> +static void __kprobes skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> + struct kprobe_ctlblk *kcb);
> /*
> * Interrupts are disabled on entry as trap3 is an interrupt gate and they
> * remain disabled throughout this function.
> @@ -599,6 +601,12 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
> } else if (kprobe_running()) {
> p = __this_cpu_read(current_kprobe);
> if (p->break_handler && p->break_handler(p, regs)) {
> +#ifdef KPROBES_CAN_USE_FTRACE
> + if (kprobe_ftrace(p)) {
> + skip_singlestep(p, regs, kcb);
> + return 1;
> + }
> +#endif
> setup_singlestep(p, regs, kcb, 0);
> return 1;
> }
> @@ -1053,6 +1061,21 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
> }
>
> #ifdef KPROBES_CAN_USE_FTRACE
> +static void __kprobes skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> + struct kprobe_ctlblk *kcb)
> +{
> + /*
> + * Emulate singlestep (and also recover regs->ip)
> + * as if there is a 5byte nop
> + */
> + regs->ip = (unsigned long)p->addr + MCOUNT_INSN_SIZE;
> + if (unlikely(p->post_handler)) {
> + kcb->kprobe_status = KPROBE_HIT_SSDONE;
> + p->post_handler(p, regs, 0);
> + }
> + __this_cpu_write(current_kprobe, NULL);
> +}
> +
> /* Ftrace callback handler for kprobes */
> void __kprobes kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> struct ftrace_ops *ops, struct pt_regs *regs)
> @@ -1077,19 +1100,12 @@ void __kprobes kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
>
> __this_cpu_write(current_kprobe, p);
> kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> - if (p->pre_handler)
> - p->pre_handler(p, regs);
> -
> - if (unlikely(p->post_handler)) {
> - /*
> - * Emulate singlestep (and also recover regs->ip)
> - * as if there is a 5byte nop
> - */
> - regs->ip = ip + MCOUNT_INSN_SIZE;
> - kcb->kprobe_status = KPROBE_HIT_SSDONE;
> - p->post_handler(p, regs, 0);
> - }
> - __this_cpu_write(current_kprobe, NULL);
> + if (!p->pre_handler || !p->pre_handler(p, regs))
> + skip_singlestep(p, regs, kcb);
> + /*
> + * If pre_handler returns !0, it sets regs->ip and
> + * resets current kprobe.
> + */
> }
> end:
> local_irq_restore(flags);
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 35b4315..098f396 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1418,9 +1418,6 @@ static __kprobes int check_kprobe_address_safe(struct kprobe *p,
> /* Given address is not on the instruction boundary */
> if ((unsigned long)p->addr != ftrace_addr)
> return -EILSEQ;
> - /* break_handler (jprobe) can not work with ftrace */
> - if (p->break_handler)
> - return -EINVAL;
> p->flags |= KPROBE_FLAG_FTRACE;
> #else /* !KPROBES_CAN_USE_FTRACE */
> return -EINVAL;
>

--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com