Commit 3cc4e2c5 authored by Ze Gao's avatar Ze Gao Committed by Masami Hiramatsu (Google)
Browse files

fprobe: make fprobe_kprobe_handler recursion free 

Current implementation calls kprobe related functions before doing
ftrace recursion check in fprobe_kprobe_handler, which opens door
to kernel crash due to stack recursion if preempt_count_{add, sub}
is traceable in kprobe_busy_{begin, end}.

Things goes like this without this patch quoted from Steven:
"
fprobe_kprobe_handler() {
   kprobe_busy_begin() {
      preempt_disable() {
         preempt_count_add() {  <-- trace
            fprobe_kprobe_handler() {
		[ wash, rinse, repeat, CRASH!!! ]
"

By refactoring the common part out of fprobe_kprobe_handler and
fprobe_handler and call ftrace recursion detection at the very beginning,
the whole fprobe_kprobe_handler is free from recursion.

[ Fix the indentation of __fprobe_handler() parameters. ]

Link: https://lore.kernel.org/all/20230517034510.15639-3-zegao@tencent.com/



Fixes: ab51e15d ("fprobe: Introduce FPROBE_FL_KPROBE_SHARED flag for fprobe")
Signed-off-by: default avatarZe Gao <zegao@tencent.com>
Acked-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
parent be243bac

kernel/trace/fprobe.c

+44 −15
Original line number Diff line number Diff line
@@ -20,30 +20,22 @@ struct fprobe_rethook_node { 
	char data[];

};



static void fprobe_handler(unsigned long ip, unsigned long parent_ip,

static inline void __fprobe_handler(unsigned long ip, unsigned long parent_ip,

			struct ftrace_ops *ops, struct ftrace_regs *fregs)

{

	struct fprobe_rethook_node *fpr;

	struct rethook_node *rh = NULL;

	struct fprobe *fp;

	void *entry_data = NULL;

	int bit, ret = 0;

	int ret = 0;



	fp = container_of(ops, struct fprobe, ops);

	if (fprobe_disabled(fp))

		return;



	bit = ftrace_test_recursion_trylock(ip, parent_ip);

	if (bit < 0) {

		fp->nmissed++;

		return;

	}



	if (fp->exit_handler) {

		rh = rethook_try_get(fp->rethook);

		if (!rh) {

			fp->nmissed++;

			goto out;

			return;

		}

		fpr = container_of(rh, struct fprobe_rethook_node, node);

		fpr->entry_ip = ip;
@@ -61,23 +53,60 @@ static void fprobe_handler(unsigned long ip, unsigned long parent_ip, 
		else

			rethook_hook(rh, ftrace_get_regs(fregs), true);

	}

out:

}



static void fprobe_handler(unsigned long ip, unsigned long parent_ip,

		struct ftrace_ops *ops, struct ftrace_regs *fregs)

{

	struct fprobe *fp;

	int bit;



	fp = container_of(ops, struct fprobe, ops);

	if (fprobe_disabled(fp))

		return;



	/* recursion detection has to go before any traceable function and

	 * all functions before this point should be marked as notrace

	 */

	bit = ftrace_test_recursion_trylock(ip, parent_ip);

	if (bit < 0) {

		fp->nmissed++;

		return;

	}

	__fprobe_handler(ip, parent_ip, ops, fregs);

	ftrace_test_recursion_unlock(bit);



}

NOKPROBE_SYMBOL(fprobe_handler);



static void fprobe_kprobe_handler(unsigned long ip, unsigned long parent_ip,

				  struct ftrace_ops *ops, struct ftrace_regs *fregs)

{

	struct fprobe *fp = container_of(ops, struct fprobe, ops);

	struct fprobe *fp;

	int bit;



	fp = container_of(ops, struct fprobe, ops);

	if (fprobe_disabled(fp))

		return;



	/* recursion detection has to go before any traceable function and

	 * all functions called before this point should be marked as notrace

	 */

	bit = ftrace_test_recursion_trylock(ip, parent_ip);

	if (bit < 0) {

		fp->nmissed++;

		return;

	}



	if (unlikely(kprobe_running())) {

		fp->nmissed++;

		return;

	}



	kprobe_busy_begin();

	fprobe_handler(ip, parent_ip, ops, fregs);

	__fprobe_handler(ip, parent_ip, ops, fregs);

	kprobe_busy_end();

	ftrace_test_recursion_unlock(bit);

}



static void fprobe_exit_handler(struct rethook_node *rh, void *data,