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    Subject[PATCH 6/9][RFC] kprobes: Allow probe on ftrace reserved text (but move it)
    From: Steven Rostedt <srostedt@redhat.com>

    If a probe is placed on a ftrace nop (or ftrace_caller), simply move the
    probe to the next instruction instead of rejecting it. This will allow
    kprobes not to be affected by ftrace using the -mfentry gcc option which
    will put the ftrace nop at the beginning of the function. As a very common
    case for kprobes is to add a probe to the very beginning of a function
    we need a way to handle the case when ftrace takes the first instruction.

    Added KPROBE_FLAG_MOVED (as suggested by Masami) that is set when the address
    is moved to get around an ftrace nop.

    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    include/linux/ftrace.h | 2 ++
    include/linux/kprobes.h | 1 +
    kernel/kprobes.c | 13 ++++++++++++-
    3 files changed, 15 insertions(+), 1 deletion(-)

    diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
    index 9310993..211ae45 100644
    --- a/include/linux/ftrace.h
    +++ b/include/linux/ftrace.h
    @@ -414,6 +414,8 @@ static inline int ftrace_text_reserved(void *start, void *end)
    #define ftrace_set_notrace(ops, buf, len, reset) ({ -ENODEV; })
    #define ftrace_free_filter(ops) do { } while (0)

    +static inline unsigned long ftrace_location(unsigned long ip) { return 0; }
    +
    static inline ssize_t ftrace_filter_write(struct file *file, const char __user *ubuf,
    size_t cnt, loff_t *ppos) { return -ENODEV; }
    static inline ssize_t ftrace_notrace_write(struct file *file, const char __user *ubuf,
    diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
    index b6e1f8c..23cf41e 100644
    --- a/include/linux/kprobes.h
    +++ b/include/linux/kprobes.h
    @@ -128,6 +128,7 @@ struct kprobe {
    * NOTE:
    * this flag is only for optimized_kprobe.
    */
    +#define KPROBE_FLAG_MOVED 8 /* probe was moved passed ftrace nop */

    /* Has this kprobe gone ? */
    static inline int kprobe_gone(struct kprobe *p)
    diff --git a/kernel/kprobes.c b/kernel/kprobes.c
    index c62b854..952619b 100644
    --- a/kernel/kprobes.c
    +++ b/kernel/kprobes.c
    @@ -1319,10 +1319,22 @@ int __kprobes register_kprobe(struct kprobe *p)
    struct kprobe *old_p;
    struct module *probed_mod;
    kprobe_opcode_t *addr;
    + unsigned long ftrace_addr;

    addr = kprobe_addr(p);
    if (IS_ERR(addr))
    return PTR_ERR(addr);
    +
    + /*
    + * If the address is located on a ftrace nop, set the
    + * breakpoint to the following instruction.
    + */
    + ftrace_addr = ftrace_location((unsigned long)addr);
    + if (unlikely(ftrace_addr)) {
    + addr = (kprobe_opcode_t *)(ftrace_addr + MCOUNT_INSN_SIZE);
    + p->flags |= KPROBE_FLAG_MOVED;
    + }
    +
    p->addr = addr;

    ret = check_kprobe_rereg(p);
    @@ -1333,7 +1345,6 @@ int __kprobes register_kprobe(struct kprobe *p)
    preempt_disable();
    if (!kernel_text_address((unsigned long) p->addr) ||
    in_kprobes_functions((unsigned long) p->addr) ||
    - ftrace_text_reserved(p->addr, p->addr) ||
    jump_label_text_reserved(p->addr, p->addr)) {
    ret = -EINVAL;
    goto cannot_probe;
    --
    1.7.9.5



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