From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 820424FC35E; Wed, 30 Sep 2026 13:37:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790775461; cv=none; b=L537CljJIPd6Nmwe/IaLaMyg1jVGMjDv3Cydmfm7O7ShydCYkJu+KOFjkYl8A1jKKF0Emup5GYh/Lu2VcrFO7D+LLMwAFkDg5Y1/mErztumWp7AbrhhlgRR7qQq4Wlv27TRyV/kdsqXnv/aGnP+KZOIhoqDhDQJMLquDUjZOAw4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790775461; c=relaxed/simple; bh=zlzB9ZxMupeywswUrXtebUKbcoIFtT/AWMqoIyrffMg=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=oyzZYMkD0sOQ5TfSURrQuGdI5dXu9E2nKF1tpZ3jfXxLej7yBuFfBDU0TiC6xz9Dd0yeQE+5QT9jhsdx81b7b3PsHhiNqCEmjR0Z6mMc0MvRyDAq4rdQAvc6o6jNEVlPgMyQlIzSU8qdp5R/Sb/k/0+Xp3TXgQNtnXKHsknOJ8E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=itHCfg7Z; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="itHCfg7Z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 792371F000FF; Wed, 30 Sep 2026 13:37:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790775448; bh=YgnrYF/r12cfEcieDzIy2DjQVqRHIKIEg5GVjZLOGsg=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=itHCfg7ZEtaJlbsoQD0HpDA7shWjfhI1FyRHvTBe4TzDHB52zGsWjr6fgAl90D7DD a75DQ/5UrHCmadawrQ/nyeqoEGjftqx+B5SB/3CoLqOo2I7plYhpcoj+bQXXWD+9qq auuyKPFXeT5QpzHX/Fy+jRiNMR9QYxfzVPItpaREjgjc3Dz8/8Gubm/jX+oa94SzMV K0hCjmZi9O6/7tlwGznM0avBZN9QkEeqzOkuO69vqauFgRcYWy97abqNcfa0FnxqD1 8ujASKGp/lmqOVo79apQKeNfug7RsDWDrYNSAq+ww3RzoogEHzNtEzxgaXzXRqmtwJ wWdfRq3TH0lGg== Date: Wed, 30 Sep 2026 22:37:24 +0900 From: Masami Hiramatsu (Google) To: Leon Hwang Cc: Naveen N Rao , "David S . Miller" , Ingo Molnar , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] kprobes: Skip disarmed probes when checking optkprobe overlap Message-Id: <20260930223724.87336536b2fe72f3732a9534@kernel.org> In-Reply-To: <20260930053618.104498-1-leon.hwang@linux.dev> References: <20260930053618.104498-1-leon.hwang@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 30 Sep 2026 13:36:18 +0800 Leon Hwang wrote: > On x86, an optkprobe at A replaces five bytes with a jump. If a disabled > probe B is at A+2, get_optimized_kprobe() stops at B when arming a new > probe C at A+4. It leaves A optimized: > > A A+1 A+2 A+3 A+4 > A's jump | e9 | d0 | d1 | d2 | d3 | > after C | e9 | d0 | d1 | d2 | cc | > > The INT3 for C overwrites the last byte of A's jump displacement, so > execution can jump to the wrong address. B can have prepared optinsns > while disarmed, but has no jump to unoptimize. Oops, good catch! get_optimized_kprobe() only checks the first disabled one and do not unoptimize the A. > > Continue past disarmed and unprepared probes to find the active optimized > probe before arming a probe in its jump. Yeah, this looks good to me. Let me send via probes/fixes. Thank you!! > > Fixes: afd66255b9a4 ("kprobes: Introduce kprobes jump optimization") > Cc: stable@vger.kernel.org > Signed-off-by: Leon Hwang > --- > kernel/kprobes.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index 6337da5cab9e..e6f6e18fa1b5 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -495,14 +495,16 @@ static bool kprobe_queued(struct kprobe *p) > static struct kprobe *get_optimized_kprobe(kprobe_opcode_t *addr) > { > int i; > - struct kprobe *p = NULL; > + struct kprobe *p; > struct optimized_kprobe *op; > > /* Don't check i == 0, since that is a breakpoint case. */ > - for (i = 1; !p && i < MAX_OPTIMIZED_LENGTH / sizeof(kprobe_opcode_t); i++) > + for (i = 1; i < MAX_OPTIMIZED_LENGTH / sizeof(kprobe_opcode_t); i++) { > p = get_kprobe(addr - i); > + /* A disabled probe can have prepared, but inactive, optinsns. */ > + if (!p || !kprobe_optready(p) || kprobe_disarmed(p)) > + continue; > > - if (p && kprobe_optready(p)) { > op = container_of(p, struct optimized_kprobe, kp); > if (arch_within_optimized_kprobe(op, addr)) > return p; > -- > 2.55.0 > -- Masami Hiramatsu (Google)