[PATCH] kretprobe: Prevent triggering kretprobe from within kprobe_flush_task
From: Jiri Olsa
Date: Wed Apr 15 2020 - 05:06:12 EST
Ziqian reported lockup when adding retprobe on _raw_spin_lock_irqsave.
My test was also able to trigger lockdep output:
============================================
WARNING: possible recursive locking detected
5.6.0-rc6+ #6 Not tainted
--------------------------------------------
sched-messaging/2767 is trying to acquire lock:
ffffffff9a492798 (&(kretprobe_table_locks[i].lock)){-.-.}, at: kretprobe_hash_lock+0x52/0xa0
but task is already holding lock:
ffffffff9a491a18 (&(kretprobe_table_locks[i].lock)){-.-.}, at: kretprobe_trampoline+0x0/0x50
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&(kretprobe_table_locks[i].lock));
lock(&(kretprobe_table_locks[i].lock));
*** DEADLOCK ***
May be due to missing lock nesting notation
1 lock held by sched-messaging/2767:
#0: ffffffff9a491a18 (&(kretprobe_table_locks[i].lock)){-.-.}, at: kretprobe_trampoline+0x0/0x50
stack backtrace:
CPU: 3 PID: 2767 Comm: sched-messaging Not tainted 5.6.0-rc6+ #6
Call Trace:
dump_stack+0x96/0xe0
__lock_acquire.cold.57+0x173/0x2b7
? native_queued_spin_lock_slowpath+0x42b/0x9e0
? lockdep_hardirqs_on+0x590/0x590
? __lock_acquire+0xf63/0x4030
lock_acquire+0x15a/0x3d0
? kretprobe_hash_lock+0x52/0xa0
_raw_spin_lock_irqsave+0x36/0x70
? kretprobe_hash_lock+0x52/0xa0
kretprobe_hash_lock+0x52/0xa0
trampoline_handler+0xf8/0x940
? kprobe_fault_handler+0x380/0x380
? find_held_lock+0x3a/0x1c0
kretprobe_trampoline+0x25/0x50
? lock_acquired+0x392/0xbc0
? _raw_spin_lock_irqsave+0x50/0x70
? __get_valid_kprobe+0x1f0/0x1f0
? _raw_spin_unlock_irqrestore+0x3b/0x40
? finish_task_switch+0x4b9/0x6d0
? __switch_to_asm+0x34/0x70
? __switch_to_asm+0x40/0x70
The code within the kretprobe handler checks for probe reentrancy,
so we won't trigger any _raw_spin_lock_irqsave probe in there.
The problem is in outside kprobe_flush_task, where we call:
kprobe_flush_task
kretprobe_table_lock
raw_spin_lock_irqsave
_raw_spin_lock_irqsave
where _raw_spin_lock_irqsave triggers the kretprobe and installs
kretprobe_trampoline handler on _raw_spin_lock_irqsave return.
The kretprobe_trampoline handler is then executed with already
locked kretprobe_table_locks, and first thing it does is to
lock kretprobe_table_locks ;-) the whole lockup path like:
kprobe_flush_task
kretprobe_table_lock
raw_spin_lock_irqsave
_raw_spin_lock_irqsave ---> probe triggered, kretprobe_trampoline installed
---> kretprobe_table_locks locked
kretprobe_trampoline
trampoline_handler
kretprobe_hash_lock(current, &head, &flags); <--- deadlock
Adding kprobe_busy_begin/end helpers that mark code with fake
probe installed to prevent triggering of another kprobe within
this code.
Using these helpers in kprobe_flush_task, so the probe recursion
protection check is hit and the probe is never set to prevent
above lockup.
Reported-by: "Ziqian SUN (Zamir)" <zsun@xxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
arch/x86/kernel/kprobes/core.c | 16 +++-------------
include/linux/kprobes.h | 4 ++++
kernel/kprobes.c | 24 ++++++++++++++++++++++++
3 files changed, 31 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 4d7022a740ab..a12adbe1559d 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -753,16 +753,11 @@ asm(
NOKPROBE_SYMBOL(kretprobe_trampoline);
STACK_FRAME_NON_STANDARD(kretprobe_trampoline);
-static struct kprobe kretprobe_kprobe = {
- .addr = (void *)kretprobe_trampoline,
-};
-
/*
* Called from kretprobe_trampoline
*/
__used __visible void *trampoline_handler(struct pt_regs *regs)
{
- struct kprobe_ctlblk *kcb;
struct kretprobe_instance *ri = NULL;
struct hlist_head *head, empty_rp;
struct hlist_node *tmp;
@@ -772,16 +767,12 @@ __used __visible void *trampoline_handler(struct pt_regs *regs)
void *frame_pointer;
bool skipped = false;
- preempt_disable();
-
/*
* Set a dummy kprobe for avoiding kretprobe recursion.
* Since kretprobe never run in kprobe handler, kprobe must not
* be running at this point.
*/
- kcb = get_kprobe_ctlblk();
- __this_cpu_write(current_kprobe, &kretprobe_kprobe);
- kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+ kprobe_busy_begin();
INIT_HLIST_HEAD(&empty_rp);
kretprobe_hash_lock(current, &head, &flags);
@@ -857,7 +848,7 @@ __used __visible void *trampoline_handler(struct pt_regs *regs)
__this_cpu_write(current_kprobe, &ri->rp->kp);
ri->ret_addr = correct_ret_addr;
ri->rp->handler(ri, regs);
- __this_cpu_write(current_kprobe, &kretprobe_kprobe);
+ __this_cpu_write(current_kprobe, &kprobe_busy);
}
recycle_rp_inst(ri, &empty_rp);
@@ -873,8 +864,7 @@ __used __visible void *trampoline_handler(struct pt_regs *regs)
kretprobe_hash_unlock(current, &flags);
- __this_cpu_write(current_kprobe, NULL);
- preempt_enable();
+ kprobe_busy_end();
hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
hlist_del(&ri->hlist);
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 04bdaf01112c..645fd401c856 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -350,6 +350,10 @@ static inline struct kprobe_ctlblk *get_kprobe_ctlblk(void)
return this_cpu_ptr(&kprobe_ctlblk);
}
+extern struct kprobe kprobe_busy;
+void kprobe_busy_begin(void);
+void kprobe_busy_end(void);
+
kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset);
int register_kprobe(struct kprobe *p);
void unregister_kprobe(struct kprobe *p);
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 2625c241ac00..75bb4a8458e7 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1236,6 +1236,26 @@ __releases(hlist_lock)
}
NOKPROBE_SYMBOL(kretprobe_table_unlock);
+struct kprobe kprobe_busy = {
+ .addr = (void *) get_kprobe,
+};
+
+void kprobe_busy_begin(void)
+{
+ struct kprobe_ctlblk *kcb;
+
+ preempt_disable();
+ __this_cpu_write(current_kprobe, &kprobe_busy);
+ kcb = get_kprobe_ctlblk();
+ kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+}
+
+void kprobe_busy_end(void)
+{
+ __this_cpu_write(current_kprobe, NULL);
+ preempt_enable();
+}
+
/*
* This function is called from finish_task_switch when task tk becomes dead,
* so that we can recycle any function-return probe instances associated
@@ -1253,6 +1273,8 @@ void kprobe_flush_task(struct task_struct *tk)
/* Early boot. kretprobe_table_locks not yet initialized. */
return;
+ kprobe_busy_begin();
+
INIT_HLIST_HEAD(&empty_rp);
hash = hash_ptr(tk, KPROBE_HASH_BITS);
head = &kretprobe_inst_table[hash];
@@ -1266,6 +1288,8 @@ void kprobe_flush_task(struct task_struct *tk)
hlist_del(&ri->hlist);
kfree(ri);
}
+
+ kprobe_busy_end();
}
NOKPROBE_SYMBOL(kprobe_flush_task);
--
2.18.2