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    Subject[PATCH 6/6 v2] kprobes/x86: Fix to support jprobes on ftrace-based kprobe
    From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

    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).

    Link: http://lkml.kernel.org/r/20120905143125.10329.90836.stgit@localhost.localdomain

    Reported-by: Fengguang Wu <fengguang.wu@intel.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    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;
    --
    1.7.10.4

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