From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 AD50EDF49 for ; Tue, 14 Oct 2025 13:00:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760446828; cv=none; b=TomLWUxnnqP4JTfw9B7TeZvNXHecH7K0blhvz2O666pI157m8D/I9sVMe9smEpmhds92iLR4CHIA30TjvuGtdOKUbhZiiaYLVsRPvtY8C/7nzjyHeEVR5ja59TqXJe3RDEmVOR18vGSm/cHDAV3dPqqwJq8f5qOcrJgejeOSHLI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760446828; c=relaxed/simple; bh=KyRyzVg30jXMn6bZNZ0rygSJ+SR+6mcaF+QaAS4lfxM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=cRX1CI6VWF2dgUMTnNSWw48QMxAJZAjKEV5mVbzyFPjBFZOyknxCOTc7y/WdB4qwZTHQvlSyBDEPGatO7Ni1Su1wrvjaG8hubEFwZP4tEUG99t9dzKhcPrZynXfUDWiOhZNr55vaN/22ZZx6+a8Q0Rm7hMxUxrKVfIrWoHZYGLY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VvptaeDj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VvptaeDj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2528C4CEE7; Tue, 14 Oct 2025 13:00:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760446828; bh=KyRyzVg30jXMn6bZNZ0rygSJ+SR+6mcaF+QaAS4lfxM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VvptaeDjxPREqhjaa16yrB2IiPS5mG1N7T4DlUBZwtuyTO3HQHjbpujwtyfC6PiqM Pp8Nr31evWZ35MykvcVjZmJt90LJX5TlwStWmvkR4HbV3iHqw7oqCCmFV7yQK+BWN+ ELZ8zLAnHofWQrIimme0I5bfEdtRCGN7jjAsGkPGozwxwR4ekYH3lqlba+yFpB8Lop QoINkkJLF1f9jHNzaE/LMBmVNCnawb9Rxk/CcP3eKnM4OJPUY+sphk2jCEqiUhxvbR 9sU4N8aRRoFY8PUzMCD/yu6fovHWxtU6v/B6eybmKoSm53qfpUn5MaqEMGU6aZd0OY 7JsicIBD7gzjA== From: Sasha Levin To: stable@vger.kernel.org Cc: Yuan Chen , "Masami Hiramatsu (Google)" , Sasha Levin Subject: [PATCH 5.4.y] tracing: Fix race condition in kprobe initialization causing NULL pointer dereference Date: Tue, 14 Oct 2025 09:00:26 -0400 Message-ID: <20251014130026.12319-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <2025101331-mulled-pueblo-7ac2@gregkh> References: <2025101331-mulled-pueblo-7ac2@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Yuan Chen [ Upstream commit 9cf9aa7b0acfde7545c1a1d912576e9bab28dc6f ] 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 = 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 = 0xffff0ad5fa89f088, //this value is correct, but x21 = 0 ... } Race Condition Analysis: The race occurs between kprobe activation and perf_events initialization: CPU0 CPU1 ==== ==== perf_kprobe_init perf_trace_event_init tp_event->perf_events = list;(1) tp_event->class->reg (2)← KPROBE ACTIVE Debug exception triggers ... kprobe_dispatcher kprobe_perf_func (tk->tp.flags & TP_FLAG_PROFILE) head = this_cpu_ptr(call->perf_events)(3) (perf_events is still NULL) Problem: 1. CPU0 executes (1) assigning tp_event->perf_events = 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 CPU1 sees that kprobe functionality is enabled but does not see that perf_events has been assigned. Add pairing read and write memory barriers to guarantee that if CPU1 sees that kprobe functionality is enabled, it must also see that perf_events has been assigned. Link: https://lore.kernel.org/all/20251001022025.44626-1-chenyuan_fl@163.com/ Fixes: 50d780560785 ("tracing/kprobes: Add probe handler dispatcher to support perf and ftrace concurrent use") Cc: stable@vger.kernel.org Signed-off-by: Yuan Chen Signed-off-by: Masami Hiramatsu (Google) [ Dropped ftrace changes + context ] Signed-off-by: Sasha Levin --- kernel/trace/trace_kprobe.c | 11 +++++++---- kernel/trace/trace_probe.h | 9 +++++++-- kernel/trace/trace_uprobe.c | 12 ++++++++---- 3 files changed, 22 insertions(+), 10 deletions(-) diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c index 56d22752a52e3..01a9fc7279c6c 100644 --- a/kernel/trace/trace_kprobe.c +++ b/kernel/trace/trace_kprobe.c @@ -1585,14 +1585,15 @@ static int kprobe_register(struct trace_event_call *event, static int kprobe_dispatcher(struct kprobe *kp, struct pt_regs *regs) { struct trace_kprobe *tk = container_of(kp, struct trace_kprobe, rp.kp); + unsigned int flags = trace_probe_load_flag(&tk->tp); int ret = 0; raw_cpu_inc(*tk->nhit); - if (trace_probe_test_flag(&tk->tp, TP_FLAG_TRACE)) + if (flags & TP_FLAG_TRACE) kprobe_trace_func(tk, regs); #ifdef CONFIG_PERF_EVENTS - if (trace_probe_test_flag(&tk->tp, TP_FLAG_PROFILE)) + if (flags & TP_FLAG_PROFILE) ret = kprobe_perf_func(tk, regs); #endif return ret; @@ -1603,13 +1604,15 @@ static int kretprobe_dispatcher(struct kretprobe_instance *ri, struct pt_regs *regs) { struct trace_kprobe *tk = container_of(ri->rp, struct trace_kprobe, rp); + unsigned int flags; raw_cpu_inc(*tk->nhit); - if (trace_probe_test_flag(&tk->tp, TP_FLAG_TRACE)) + flags = trace_probe_load_flag(&tk->tp); + if (flags & TP_FLAG_TRACE) kretprobe_trace_func(tk, ri, regs); #ifdef CONFIG_PERF_EVENTS - if (trace_probe_test_flag(&tk->tp, TP_FLAG_PROFILE)) + if (flags & TP_FLAG_PROFILE) kretprobe_perf_func(tk, ri, regs); #endif return 0; /* We don't tweek kernel, so just return 0 */ diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h index edbb1624061ed..15c9ef34a611e 100644 --- a/kernel/trace/trace_probe.h +++ b/kernel/trace/trace_probe.h @@ -252,16 +252,21 @@ struct event_file_link { struct list_head list; }; +static inline unsigned int trace_probe_load_flag(struct trace_probe *tp) +{ + return smp_load_acquire(&tp->event->flags); +} + static inline bool trace_probe_test_flag(struct trace_probe *tp, unsigned int flag) { - return !!(tp->event->flags & flag); + return !!(trace_probe_load_flag(tp) & flag); } static inline void trace_probe_set_flag(struct trace_probe *tp, unsigned int flag) { - tp->event->flags |= flag; + smp_store_release(&tp->event->flags, tp->event->flags | flag); } static inline void trace_probe_clear_flag(struct trace_probe *tp, diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index e924c04af627e..4f844df6ee000 100644 --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -1465,6 +1465,7 @@ static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs) struct uprobe_dispatch_data udd; struct uprobe_cpu_buffer *ucb; int dsize, esize; + unsigned int flags; int ret = 0; @@ -1485,11 +1486,12 @@ static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs) ucb = uprobe_buffer_get(); store_trace_args(ucb->buf, &tu->tp, regs, esize, dsize); - if (trace_probe_test_flag(&tu->tp, TP_FLAG_TRACE)) + flags = trace_probe_load_flag(&tu->tp); + if (flags & TP_FLAG_TRACE) ret |= uprobe_trace_func(tu, regs, ucb, dsize); #ifdef CONFIG_PERF_EVENTS - if (trace_probe_test_flag(&tu->tp, TP_FLAG_PROFILE)) + if (flags & TP_FLAG_PROFILE) ret |= uprobe_perf_func(tu, regs, ucb, dsize); #endif uprobe_buffer_put(ucb); @@ -1503,6 +1505,7 @@ static int uretprobe_dispatcher(struct uprobe_consumer *con, struct uprobe_dispatch_data udd; struct uprobe_cpu_buffer *ucb; int dsize, esize; + unsigned int flags; tu = container_of(con, struct trace_uprobe, consumer); @@ -1520,11 +1523,12 @@ static int uretprobe_dispatcher(struct uprobe_consumer *con, ucb = uprobe_buffer_get(); store_trace_args(ucb->buf, &tu->tp, regs, esize, dsize); - if (trace_probe_test_flag(&tu->tp, TP_FLAG_TRACE)) + flags = trace_probe_load_flag(&tu->tp); + if (flags & TP_FLAG_TRACE) uretprobe_trace_func(tu, func, regs, ucb, dsize); #ifdef CONFIG_PERF_EVENTS - if (trace_probe_test_flag(&tu->tp, TP_FLAG_PROFILE)) + if (flags & TP_FLAG_PROFILE) uretprobe_perf_func(tu, func, regs, ucb, dsize); #endif uprobe_buffer_put(ucb); -- 2.51.0