Subject: [RFC PATCH v4 27/34] early kprobes on ftrace: kprobe_on_ftrace_get_old_insn()

From: [email-masked] (Wang Nan)
Date: Wed, 4 Mar 2015 10:30:24 +0800

On 2015/3/2 22:25, Wang Nan wrote:
> Newly introduced function kprobe_on_ftrace_get_old_insn() will be
> called by ftrace when ftrace generating call instruction. It is for
> retriving probed instructions which original nops are replaced by
> kprobe. FTRACE_FL_EARLY_KPROBES bit in rec->flags is cleared, so after
> calling kprobe_on_ftrace_get_old_insn() an ftrace record will not be
> treated as early kprobed.
> 
> Signed-off-by: Wang Nan <[email-masked]>
> ---
>  include/linux/kprobes.h |  9 +++++++++
>  kernel/kprobes.c        | 34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 43 insertions(+)
> 
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 5a5290f..2d78bbb 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -289,6 +289,8 @@ extern const unsigned char *arch_kprobe_on_ftrace_get_old_insn(struct kprobe *kp
>  
>  extern void init_kprobes_on_ftrace(void);
>  extern bool kprobe_fix_ftrace_make_nop(struct dyn_ftrace *rec);
> +extern const unsigned char *kprobe_on_ftrace_get_old_insn(struct dyn_ftrace *rec,
> +		const unsigned char *ftrace_nop, unsigned char *dest, size_t insn_size);
>  #else
>  static inline void init_kprobes_on_ftrace(void)
>  {
> @@ -299,6 +301,13 @@ static inline bool kprobe_fix_ftrace_make_nop(struct dyn_ftrace *_unused)
>  
>  	return false;
>  }
> +
> +static inline const unsigned char *
> +kprobe_on_ftrace_get_old_insn(struct dyn_ftrace *_unused,
> +		const unsigned char *ftrace_nop, unsigned char *_unused2, size_t _unused3)
> +{
> +	return ftrace_nop;
> +}
>  #endif // CONFIG_EARLY_KPROBES && CONFIG_KPROBES_ON_FTRACE
>  
>  #ifdef CONFIG_EARLY_KPROBES
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 20b6ab8..c504c1c 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2623,6 +2623,40 @@ bool kprobe_fix_ftrace_make_nop(struct dyn_ftrace *rec)
>  	return true;
>  }
>  
> +/* NOTE: caller must ensure holding kprobe_mutex */
> +const unsigned char *
> +kprobe_on_ftrace_get_old_insn(struct dyn_ftrace *rec,
> +		const unsigned char *ftrace_nop,
> +		unsigned char *dest, size_t insn_size)
> +{
> +	const unsigned char *ret;
> +	struct kprobe *kp;
> +	void *addr;
> +
> +	if (!(rec->flags & FTRACE_FL_EARLY_KPROBES))
> +		return ftrace_nop;
> +
> +	addr = (void *)rec->ip;
> +
> +	/*
> +	 * Note that get_kprobe always get the kprobe on table, for it
> +	 * KPROBE_FLAG_OPTIMIZED is reliable.
> +	 */
> +	kp = get_kprobe(addr);
> +
> +	if (!kp || !(kp->flags & KPROBE_FLAG_FTRACE_EARLY)) {
> +		mutex_unlock(&kprobe_mutex);

This mutex_unlock() is buggy. I'll fix it in next version.

> +		return ftrace_nop;
> +	}
> +
> +	ret = arch_kprobe_on_ftrace_get_old_insn(kp, ftrace_nop,
> +			dest, insn_size);
> +
> +	/* Only give one chance for kprobe to retrive old insn. */
> +	rec->flags &= ~FTRACE_FL_EARLY_KPROBES;
> +	return ret;
> +}
> +
>  void init_kprobes_on_ftrace(void)
>  {
>  	kprobes_on_ftrace_initialized = true;
>