Messages in this thread Patch in this message | | | From | Masami Hiramatsu <> | Subject | [BUGFIX PATCH tip/master V2 3/3] kprobes/arm: Fix a possible deadlock case in kretprobe | Date | Fri, 10 Feb 2017 01:32:22 +0900 |
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Fix a possibility of deadlock case in kretprobe on arm implementation. There may be a chance that the kretprobe hash table lock can cause a dead lock.
The senario is that a user puts 2 kretprobes, one on normal function and one on a function which can be called from somewhare which can interrupt in irq disabled critical section like FIQ.
In this case, if the kernel hits the 1st kretprobe on a normal function return which calls trampoline_handler(), acquire a spinlock on the hash table in kretprobe_hash_lock() and disable irqs. After that, if the 2nd kretprobe is kicked from FIQ, it also calls trampoline_handler() and tries to acquire the same spinlock (since the hash is based on current task, same as the 1st kretprobe), it causes a deadlock.
Actually, this bug has been introduced by kretprobe-booster which removes a kprobe from return trampoline code, but also resets current kprobe, which can be a stopper for the nested k(ret)probes.
To fix this issue, I introduced a dummy kprobe which is set as a current kprobe while holding the kretprobe-hash lock. With that, if the 2nd kretprobe's kprobe is kicked (to modify the return address, a kprobe is kicked when the target function is called), that kprobe (and the 2nd kretprobe also) is skipped because it detects there is another kprobe is running.
This reentrance detection and nested kprobe blocker had existed when the original kretprobe was implemented by using a kprobe on trampoline code. This fixes just revived it.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> --- arch/arm/probes/kprobes/core.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c index b6dc9d8..3e5aab7 100644 --- a/arch/arm/probes/kprobes/core.c +++ b/arch/arm/probes/kprobes/core.c @@ -426,6 +426,8 @@ void __naked __kprobes kretprobe_trampoline(void) : : : "memory"); } +static struct kprobe dummy_retprobe = {.addr = (void *)&kretprobe_trampoline}; + /* Called from kretprobe_trampoline */ static __used __kprobes void *trampoline_handler(struct pt_regs *regs) { @@ -436,6 +438,11 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs) unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline; INIT_HLIST_HEAD(&empty_rp); + + /* This prevents kernel to change running cpu while processing */ + preempt_disable(); + get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE; + __this_cpu_write(current_kprobe, &dummy_retprobe); kretprobe_hash_lock(current, &head, &flags); /* @@ -458,9 +465,8 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs) if (ri->rp && ri->rp->handler) { __this_cpu_write(current_kprobe, &ri->rp->kp); - get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE; ri->rp->handler(ri, regs); - __this_cpu_write(current_kprobe, NULL); + __this_cpu_write(current_kprobe, &dummy_retprobe); } orig_ret_address = (unsigned long)ri->ret_addr; @@ -477,6 +483,8 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs) kretprobe_assert(ri, orig_ret_address, trampoline_address); kretprobe_hash_unlock(current, &flags); + __this_cpu_write(current_kprobe, NULL); + preempt_enable_no_resched(); hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) { hlist_del(&ri->hlist);
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