fprobe_hander and fprobe_kprobe_handler has guarded ftrace recusion
detection but fprobe_exit_handler has not, which possibly introduce
recurive 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 recusion free guard the same way as fprobe_hander and also
mark fprobe_exit_handler notrace. Since ftrace recursion check does
not employ ips, so here use entry_ip and entry_parent_ip the same as
fprobe_handler.
Signed-off-by: Ze Gao <[email protected]>
---
kernel/trace/fprobe.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index ad9a36c87ad9..cf982d4ab142 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 notrace 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;
}
@@ -109,19 +111,30 @@ static void notrace fprobe_kprobe_handler(unsigned long ip, unsigned long parent
ftrace_test_recursion_unlock(bit);
}
-static void fprobe_exit_handler(struct rethook_node *rh, void *data,
+static void notrace fprobe_exit_handler(struct rethook_node *rh, void *data,
struct pt_regs *regs)
{
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
On Mon, 15 May 2023 11:26:40 +0800
Ze Gao <[email protected]> wrote:
> fprobe_hander and fprobe_kprobe_handler has guarded ftrace recusion
> detection but fprobe_exit_handler has not, which possibly introduce
> recurive 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.
Good catch! Yes, this can fix such recursive call case because if
we put a fprobe to the exit of the "func()", recursive call happens
as below;
func() {
} => rethook
=> fprobe_exit_handler()
=> fp->exit_handler() {
func() {
} => rethook
=> fprobe_exit_handler()
=> fp->exit_handler() {
func() {
} => rethook ...
Note that this should not happen with fprobe-based events because
all the code (except for tests) under kernel/trace/ are marked
notrace automatically.
kretprobe avoids this by setting itself to current_kprobe, thus the
other kprobes recursively called from the rethook will be skipped.
>
> So add recusion free guard the same way as fprobe_hander and also
> mark fprobe_exit_handler notrace. Since ftrace recursion check does
> not employ ips, so here use entry_ip and entry_parent_ip the same as
> fprobe_handler.
Looks good to me.
Fixes: 5b0ab78998e3 ("fprobe: Add exit_handler support")
Cc: [email protected]
Acked-by: Masami Hiramatsu (Google) <[email protected]>
>
> Signed-off-by: Ze Gao <[email protected]>
> ---
> kernel/trace/fprobe.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index ad9a36c87ad9..cf982d4ab142 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 notrace 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;
> }
> @@ -109,19 +111,30 @@ static void notrace fprobe_kprobe_handler(unsigned long ip, unsigned long parent
> ftrace_test_recursion_unlock(bit);
> }
>
> -static void fprobe_exit_handler(struct rethook_node *rh, void *data,
> +static void notrace fprobe_exit_handler(struct rethook_node *rh, void *data,
> struct pt_regs *regs)
> {
> 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
>
--
Masami Hiramatsu (Google) <[email protected]>