From nobody Wed Oct 1 22:37:07 2025 Received: from m16.mail.163.com (m16.mail.163.com [220.197.31.2]) (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 057CB24E4A8; Mon, 29 Sep 2025 06:58:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.2 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759129119; cv=none; b=i76ZBz4ve21jWaaPonYtp5mTp2W0NZO0q9n3NVmBN1vHTtKjjJHYfczLZlura6Axr6C46SQztobdW8yxrO0w+0jWg3but4ximofBT6JP9AQj5qCWxZpkIGXLcoOvouccPwBFYtDs5INly9qRv3L9yHk+fQQMCecSgOg4EGeaKt0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759129119; c=relaxed/simple; bh=R7ZZLa2uq2OopMNumMfKiotQ6l8ZXgsGUvlznSbAEM0=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=nL9uTtJGeNVWqdJ/yJoFSX8Mq0QuyQVZMSzZfsQxISNVXPYmTZ5qEpMFpVdFUDyJCFY6KIIc1OjGjOOzWS9Sc4L7+ddo6B8ImIAWfAYpsBfmd+goZh5AChzlW+axGOeCfAcAHujxV8l1aXnpc8ED4ftzZpugear0JLjEX+H3oVk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com; spf=pass smtp.mailfrom=163.com; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b=N/rXDqQz; arc=none smtp.client-ip=220.197.31.2 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=163.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b="N/rXDqQz" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=163.com; s=s110527; h=From:To:Subject:Date:Message-Id:MIME-Version: Content-Type; bh=Gm8qfoQPoH+ievQnWuMi3d0xrbwVYPSrrYvoJdhijto=; b=N/rXDqQzwfmZBa3ZKYb4uxdu7Dcv46G25xwCSu1bPEcO7lg/Bhh3mYPh1BH4JB 3DM1U66VMtJitcdRrTwHTLBP1dWb9KCUSEYz4ALYY+sGZJ/eVOPgxJKu6Or7dmRa 8u6jWsmmx2Fb2N0KazHm3MqQmKE1eRiu8CPqq6SkRQplc= Received: from 163.com (unknown []) by gzga-smtp-mtada-g1-4 (Coremail) with SMTP id _____wDnb3rdLdpoXE62Aw--.14177S2; Mon, 29 Sep 2025 14:57:33 +0800 (CST) From: chenyuan_fl@163.com To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Yuan Chen Subject: [PATCH v2] tracing: Fix race condition in kprobe initialization causing NULL pointer dereference Date: Mon, 29 Sep 2025 07:57:31 +0100 Message-Id: <20250929065731.1351028-1-chenyuan_fl@163.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250929143916.5984441b32e6f84618b4deb8@kernel.org> References: <20250929143916.5984441b32e6f84618b4deb8@kernel.org> 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="utf-8" Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: _____wDnb3rdLdpoXE62Aw--.14177S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxZw4fZw4fZFW8Cr17Xr17trb_yoWrtF17pa nxKw45Kw4kJFyjqryrJr1UA3W7JFyrAFWDJry7Gw45ZF4jgr1UtF12qayUAF13GFWDAFyf J3ZIqr10vryUJaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jo1v3UUUUU= X-CM-SenderInfo: xfkh05pxdqswro6rljoofrz/1tbiJxvXvWjaK+gmjwAAsO From: Yuan Chen There is a critical race condition in kprobe initialization that can lead to NULL pointer dereference and kernel crash. [1135630.084782] Unable to handle kernel paging request at virtual address = 0000710a04630000 ... [1135630.260314] pstate: 404003c9 (nZcv DAIF +PAN -UAO) [1135630.269239] pc : kprobe_perf_func+0x30/0x260 [1135630.277643] lr : kprobe_dispatcher+0x44/0x60 [1135630.286041] sp : ffffaeff4977fa40 [1135630.293441] x29: ffffaeff4977fa40 x28: ffffaf015340e400 [1135630.302837] x27: 0000000000000000 x26: 0000000000000000 [1135630.312257] x25: ffffaf029ed108a8 x24: ffffaf015340e528 [1135630.321705] x23: ffffaeff4977fc50 x22: ffffaeff4977fc50 [1135630.331154] x21: 0000000000000000 x20: ffffaeff4977fc50 [1135630.340586] x19: ffffaf015340e400 x18: 0000000000000000 [1135630.349985] x17: 0000000000000000 x16: 0000000000000000 [1135630.359285] x15: 0000000000000000 x14: 0000000000000000 [1135630.368445] x13: 0000000000000000 x12: 0000000000000000 [1135630.377473] x11: 0000000000000000 x10: 0000000000000000 [1135630.386411] x9 : 0000000000000000 x8 : 0000000000000000 [1135630.395252] x7 : 0000000000000000 x6 : 0000000000000000 [1135630.403963] x5 : 0000000000000000 x4 : 0000000000000000 [1135630.412545] x3 : 0000710a04630000 x2 : 0000000000000006 [1135630.421021] x1 : ffffaeff4977fc50 x0 : 0000710a04630000 [1135630.429410] Call trace: [1135630.434828] kprobe_perf_func+0x30/0x260 [1135630.441661] kprobe_dispatcher+0x44/0x60 [1135630.448396] aggr_pre_handler+0x70/0xc8 [1135630.454959] kprobe_breakpoint_handler+0x140/0x1e0 [1135630.462435] brk_handler+0xbc/0xd8 [1135630.468437] do_debug_exception+0x84/0x138 [1135630.475074] el1_dbg+0x18/0x8c [1135630.480582] security_file_permission+0x0/0xd0 [1135630.487426] vfs_write+0x70/0x1c0 [1135630.493059] ksys_write+0x5c/0xc8 [1135630.498638] __arm64_sys_write+0x24/0x30 [1135630.504821] el0_svc_common+0x78/0x130 [1135630.510838] el0_svc_handler+0x38/0x78 [1135630.516834] el0_svc+0x8/0x1b0 kernel/trace/trace_kprobe.c: 1308 0xffff3df8995039ec : ldr x21, [x24,#120] include/linux/compiler.h: 294 0xffff3df8995039f0 : ldr x1, [x21,x0] kernel/trace/trace_kprobe.c 1308: head =3D this_cpu_ptr(call->perf_events); 1309: if (hlist_empty(head)) 1310: return 0; crash> struct trace_event_call -o struct trace_event_call { ... [120] struct hlist_head *perf_events; //(call->perf_event) ... } crash> struct trace_event_call ffffaf015340e528 struct trace_event_call { ... perf_events =3D 0xffff0ad5fa89f088, //this value is correct, but x21 =3D 0 ... } Race Condition Analysis: The race occurs between kprobe activation and perf_events initialization: CPU0 CPU1 =3D=3D=3D=3D =3D=3D=3D=3D perf_kprobe_init perf_trace_event_init tp_event->perf_events =3D list;(1) tp_event->class->reg (2)=E2=86=90 KPROBE ACTIVE Debug exception triggers ... kprobe_dispatcher kprobe_perf_func (tk->tp.flags = & TP_FLAG_PROFILE) head =3D this_cpu_ptr(call->p= erf_events)(3) (perf_events is still NULL) Problem: 1. CPU0 executes (1) assigning tp_event->perf_events =3D list 2. CPU0 executes (2) enabling kprobe functionality via class->reg() 3. CPU1 triggers and reaches kprobe_dispatcher 4. CPU1 checks TP_FLAG_PROFILE - condition passes (step 2 completed) 5. CPU1 calls kprobe_perf_func() and crashes at (3) because call->perf_events is still NULL The issue: Assignment in step 1 may not be visible to CPU1 due to missing memory barriers before step 2 sets TP_FLAG_PROFILE flag. Add smp_mb() barrier between perf_events assignment and enabling profile functionality to ensure visibility ordering across CPUs. v1->v2: Fix race analysis (per Masami) - kprobe arms in class->reg(). Signed-off-by: Yuan Chen --- kernel/trace/trace_event_perf.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_per= f.c index a6bb7577e8c5..6eff8c9d6bae 100644 --- a/kernel/trace/trace_event_perf.c +++ b/kernel/trace/trace_event_perf.c @@ -113,6 +113,11 @@ static int perf_trace_event_reg(struct trace_event_cal= l *tp_event, =20 tp_event->perf_events =3D list; =20 + /* Ensure perf_events assignment is visible to all CPUs before enabling + * profile functionality + */ + smp_mb(); + if (!total_ref_count) { char __percpu *buf; int i; --=20 2.39.5