linux-kernel - [PATCH v3 3/4] fprobe: add recursion detection in fprobe_exit

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Date:   Wed, 17 May 2023 11:45:08 +0800
From:   Ze Gao <zegao2021@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Albert Ou <aou@...s.berkeley.edu>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>, x86@...nel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org,
        Conor Dooley <conor@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Yonghong Song <yhs@...com>, Ze Gao <zegao@...cent.com>,
        stable@...r.kernel.org
Subject: [PATCH v3 3/4] fprobe: add recursion detection in fprobe_exit_handler

fprobe_hander and fprobe_kprobe_handler has guarded ftrace recursion
detection but fprobe_exit_handler has not, which possibly introduce
recursive calls if the fprobe exit callback calls any traceable
functions. Checking in fprobe_hander or fprobe_kprobe_handler
is not enough and misses this case.

So add recursion free guard the same way as fprobe_hander. Since
ftrace recursion check does not employ ip(s), so here use entry_ip and
entry_parent_ip the same as fprobe_handler.

Fixes: 5b0ab78998e3 ("fprobe: Add exit_handler support")
Signed-off-by: Ze Gao <zegao@...cent.com>
Cc: stable@...r.kernel.org
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Link: https://lore.kernel.org/linux-trace-kernel/20230516071830.8190-4-zegao@tencent.com
---
 kernel/trace/fprobe.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 097c740799ba..281b58c7dd14 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -17,6 +17,7 @@
 struct fprobe_rethook_node {
 	struct rethook_node node;
 	unsigned long entry_ip;
+	unsigned long entry_parent_ip;
 	char data[];
 };
 
@@ -39,6 +40,7 @@ static inline void __fprobe_handler(unsigned long ip, unsigned long
 		}
 		fpr = container_of(rh, struct fprobe_rethook_node, node);
 		fpr->entry_ip = ip;
+		fpr->entry_parent_ip = parent_ip;
 		if (fp->entry_data_size)
 			entry_data = fpr->data;
 	}
@@ -114,14 +116,26 @@ static void fprobe_exit_handler(struct rethook_node *rh, void *data,
 {
 	struct fprobe *fp = (struct fprobe *)data;
 	struct fprobe_rethook_node *fpr;
+	int bit;
 
 	if (!fp || fprobe_disabled(fp))
 		return;
 
 	fpr = container_of(rh, struct fprobe_rethook_node, node);
 
+	/*
+	 * we need to assure no calls to traceable functions in-between the
+	 * end of fprobe_handler and the beginning of fprobe_exit_handler.
+	 */
+	bit = ftrace_test_recursion_trylock(fpr->entry_ip, fpr->entry_parent_ip);
+	if (bit < 0) {
+		fp->nmissed++;
+		return;
+	}
+
 	fp->exit_handler(fp, fpr->entry_ip, regs,
 			 fp->entry_data_size ? (void *)fpr->data : NULL);
+	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(fprobe_exit_handler);
 
-- 
2.40.1