linux-kernel - Re: [PATCH 2/3] x86/kprobes: Fix __recover_optprobed

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Message-Id: <20230216000849.f0e332ebf35150cb5d5c4a29@kernel.org>
Date:   Thu, 16 Feb 2023 00:08:49 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Yang Jihong <yangjihong1@...wei.com>
Cc:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
        <naveen.n.rao@...ux.ibm.com>, <anil.s.keshavamurthy@...el.com>,
        <davem@...emloft.net>, <ast@...nel.org>, <peterz@...radead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] x86/kprobes: Fix __recover_optprobed_insn check
 optimizing logic

On Wed, 15 Feb 2023 19:54:29 +0800
Yang Jihong <yangjihong1@...wei.com> wrote:

> Since the following commit:
> 
>   commit f66c0447cca1 ("kprobes: Set unoptimized flag after unoptimizing code")
> 
> modified the update timing of the KPROBE_FLAG_OPTIMIZED, a optimized_kprobe
> may be in the optimizing or unoptimizing state when op.kp->flags
> has KPROBE_FLAG_OPTIMIZED and op->list is not empty.
> 
> The __recover_optprobed_insn check logic is incorrect, a kprobe in the
> unoptimizing state may be incorrectly determined as unoptimizing.
> As a result, incorrect instructions are copied.

Ah, good catch!

> 
> The optprobe_queued_unopt function needs to be exported for invoking in
> arch directory.
> 
> Fixes: f66c0447cca1 ("kprobes: Set unoptimized flag after unoptimizing code")

Cc: stable@...r.kernel.org

> Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
> ---
>  arch/x86/kernel/kprobes/opt.c | 4 ++--
>  include/linux/kprobes.h       | 1 +
>  kernel/kprobes.c              | 2 +-
>  3 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
> index e57e07b0edb6..3718d6863555 100644
> --- a/arch/x86/kernel/kprobes/opt.c
> +++ b/arch/x86/kernel/kprobes/opt.c
> @@ -46,8 +46,8 @@ unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
>  		/* This function only handles jump-optimized kprobe */
>  		if (kp && kprobe_optimized(kp)) {
>  			op = container_of(kp, struct optimized_kprobe, kp);
> -			/* If op->list is not empty, op is under optimizing */
> -			if (list_empty(&op->list))
> +			/* If op is [un]optimized or under unoptimizing */

Hmm, this is a bit confusing comment. If it is unoptimized, the kprobe_optimized() returns false.
Thus the comment should be /* If op is optimized or under unoptimizing */.

Thank you,

> +			if (list_empty(&op->list) || optprobe_queued_unopt(op))
>  				goto found;
>  		}
>  	}
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index a0b92be98984..ab39285f71a6 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -378,6 +378,7 @@ extern void opt_pre_handler(struct kprobe *p, struct pt_regs *regs);
>  DEFINE_INSN_CACHE_OPS(optinsn);
>  
>  extern void wait_for_kprobe_optimizer(void);
> +bool optprobe_queued_unopt(struct optimized_kprobe *op);
>  #else /* !CONFIG_OPTPROBES */
>  static inline void wait_for_kprobe_optimizer(void) { }
>  #endif /* CONFIG_OPTPROBES */
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 0730e595f4c1..bf60eb26c873 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -661,7 +661,7 @@ void wait_for_kprobe_optimizer(void)
>  	mutex_unlock(&kprobe_mutex);
>  }
>  
> -static bool optprobe_queued_unopt(struct optimized_kprobe *op)
> +bool optprobe_queued_unopt(struct optimized_kprobe *op)
>  {
>  	struct optimized_kprobe *_op;
>  
> -- 
> 2.30.GIT
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>