5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Yuan Chen chenyuan@kylinos.cn
[ 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 <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.
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 chenyuan@kylinos.cn Signed-off-by: Masami Hiramatsu (Google) mhiramat@kernel.org [ Dropped ftrace changes + context ] Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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(-)
--- a/kernel/trace/trace_kprobe.c +++ b/kernel/trace/trace_kprobe.c @@ -1585,14 +1585,15 @@ static int kprobe_register(struct trace_ 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 */ --- 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, --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -1465,6 +1465,7 @@ static int uprobe_dispatcher(struct upro 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 upro 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 u 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 u 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);