Re: [PATCH v3 2/4] fprobe: make fprobe_kprobe_handler recursion free
From: Jiri Olsa <hidden>
Date: 2023-05-17 10:47:51
Also in:
bpf, linux-riscv, linux-s390, lkml
Subsystem:
the rest, tracing · Maintainers:
Linus Torvalds, Steven Rostedt, Masami Hiramatsu
On Wed, May 17, 2023 at 11:45:07AM +0800, Ze Gao wrote:
quoted hunk ↗ jump to hunk
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. Signed-off-by: Ze Gao <redacted> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Link: https://lore.kernel.org/linux-trace-kernel/20230516071830.8190-3-zegao@tencent.com (local) --- kernel/trace/fprobe.c | 59 ++++++++++++++++++++++++++++++++----------- 1 file changed, 44 insertions(+), 15 deletions(-)diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c index 9abb3905bc8e..097c740799ba 100644 --- a/kernel/trace/fprobe.c +++ b/kernel/trace/fprobe.c@@ -20,30 +20,22 @@ struct fprobe_rethook_node { char data[]; }; -static void fprobe_handler(unsigned long ip, unsigned long parent_ip, - struct ftrace_ops *ops, struct ftrace_regs *fregs) +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; + int ret;
this change uncovered bug for me introduced by [1] the bpf's kprobe multi uses either fprobe's entry_handler or exit_handler, so the 'ret' value is undefined for return probe path and occasionally we won't setup rethook and miss the return probe we can either squash this change into your patch or I can make separate patch for that.. but given that [1] is quite recent we could just silently fix that ;-) jirka [1] 39d954200bf6 fprobe: Skip exit_handler if entry_handler returns !0 ---
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 9abb3905bc8e..293184227394 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c@@ -27,7 +27,7 @@ static void fprobe_handler(unsigned long ip, unsigned long parent_ip, struct rethook_node *rh = NULL; struct fprobe *fp; void *entry_data = NULL; - int bit, ret; + int bit, ret = 0; fp = container_of(ops, struct fprobe, ops); if (fprobe_disabled(fp))