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Message-Id: <20251001022025.44626-1-chenyuan_fl@163.com>
Date: Wed, 1 Oct 2025 03:20:25 +0100
From: chenyuan_fl@....com
To: mhiramat@...nel.org
Cc: bigeasy@...utronix.de,
chenyuan@...inos.cn,
chenyuan_fl@....com,
john.ogness@...utronix.de,
linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org,
mathieu.desnoyers@...icios.com,
peterz@...radead.org,
rostedt@...dmis.org
Subject: [PATCH v4] tracing: Fix race condition in kprobe initialization causing NULL pointer dereference
From: Yuan Chen <chenyuan@...inos.cn>
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 <kprobe_perf_func+0x2c>: ldr x21, [x24,#120]
include/linux/compiler.h: 294
0xffff3df8995039f0 <kprobe_perf_func+0x30>: 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.
v1->v2: Fix race analysis (per Masami) - kprobe arms in class->reg().
v2->v3: Adopt RELEASE/ACQUIRE semantics per Peter/John's suggestions,
aligning with Steven's clarification on barrier purposes.
v3->v4: Introduce load_flag() (Masami) and optimize barrier usage in
checks/clear (Peter).
Signed-off-by: Yuan Chen <chenyuan@...inos.cn>
---
kernel/trace/trace_fprobe.c | 10 ++++++----
kernel/trace/trace_kprobe.c | 11 +++++++----
kernel/trace/trace_probe.h | 9 +++++++--
kernel/trace/trace_uprobe.c | 12 ++++++++----
4 files changed, 28 insertions(+), 14 deletions(-)
diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index b36ade43d4b3..ad9d6347b5fa 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -522,13 +522,14 @@ static int fentry_dispatcher(struct fprobe *fp, unsigned long entry_ip,
void *entry_data)
{
struct trace_fprobe *tf = container_of(fp, struct trace_fprobe, fp);
+ unsigned int flags = trace_probe_load_flag(&tf->tp);
int ret = 0;
- if (trace_probe_test_flag(&tf->tp, TP_FLAG_TRACE))
+ if (flags & TP_FLAG_TRACE)
fentry_trace_func(tf, entry_ip, fregs);
#ifdef CONFIG_PERF_EVENTS
- if (trace_probe_test_flag(&tf->tp, TP_FLAG_PROFILE))
+ if (flags & TP_FLAG_PROFILE)
ret = fentry_perf_func(tf, entry_ip, fregs);
#endif
return ret;
@@ -540,11 +541,12 @@ static void fexit_dispatcher(struct fprobe *fp, unsigned long entry_ip,
void *entry_data)
{
struct trace_fprobe *tf = container_of(fp, struct trace_fprobe, fp);
+ unsigned int flags = trace_probe_load_flag(&tf->tp);
- if (trace_probe_test_flag(&tf->tp, TP_FLAG_TRACE))
+ if (flags & TP_FLAG_TRACE)
fexit_trace_func(tf, entry_ip, ret_ip, fregs, entry_data);
#ifdef CONFIG_PERF_EVENTS
- if (trace_probe_test_flag(&tf->tp, TP_FLAG_PROFILE))
+ if (flags & TP_FLAG_PROFILE)
fexit_perf_func(tf, entry_ip, ret_ip, fregs, entry_data);
#endif
}
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index ccae62d4fb91..b1b793b8f191 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1813,14 +1813,15 @@ 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;
@@ -1832,6 +1833,7 @@ kretprobe_dispatcher(struct kretprobe_instance *ri, struct pt_regs *regs)
{
struct kretprobe *rp = get_kretprobe(ri);
struct trace_kprobe *tk;
+ unsigned int flags;
/*
* There is a small chance that get_kretprobe(ri) returns NULL when
@@ -1844,10 +1846,11 @@ kretprobe_dispatcher(struct kretprobe_instance *ri, struct pt_regs *regs)
tk = container_of(rp, struct trace_kprobe, rp);
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 tweak kernel, so just return 0 */
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 842383fbc03b..08b5bda24da2 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -271,16 +271,21 @@ 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 8b0bcc0d8f41..430d09c49462 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -1547,6 +1547,7 @@ static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs,
struct trace_uprobe *tu;
struct uprobe_dispatch_data udd;
struct uprobe_cpu_buffer *ucb = NULL;
+ unsigned int flags;
int ret = 0;
tu = container_of(con, struct trace_uprobe, consumer);
@@ -1561,11 +1562,12 @@ static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs,
if (WARN_ON_ONCE(!uprobe_cpu_buffer))
return 0;
- 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);
#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);
#endif
uprobe_buffer_put(ucb);
@@ -1579,6 +1581,7 @@ static int uretprobe_dispatcher(struct uprobe_consumer *con,
struct trace_uprobe *tu;
struct uprobe_dispatch_data udd;
struct uprobe_cpu_buffer *ucb = NULL;
+ unsigned int flags;
tu = container_of(con, struct trace_uprobe, consumer);
@@ -1590,11 +1593,12 @@ static int uretprobe_dispatcher(struct uprobe_consumer *con,
if (WARN_ON_ONCE(!uprobe_cpu_buffer))
return 0;
- 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);
#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);
#endif
uprobe_buffer_put(ucb);
--
2.39.5
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