Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
livepatch"), in a scenario where livepatch and kprobe coexist on the
same function entry, the creation of kprobe_event using
add_kprobe_event_legacy() will be successful, at the same time as a
trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
perf_event_open() will return an error because both livepatch and kprobe
use FTRACE_OPS_FL_IPMODIFY.
With this patch, whenever an error is returned after
add_kprobe_event_legacy(), this ensures that the created kprobe_event is
cleaned.
Signed-off-by: Chuang W <[email protected]>
Signed-off-by: Jingren Zhou <[email protected]>
---
tools/lib/bpf/libbpf.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0781fae58a06..d0a36350e22a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10809,10 +10809,11 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
}
type = determine_kprobe_perf_type_legacy(probe_name, retprobe);
if (type < 0) {
+ err = type;
pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",
kfunc_name, offset,
- libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
- return type;
+ libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+ goto clear_kprobe_event;
}
attr.size = sizeof(attr);
attr.config = type;
@@ -10826,9 +10827,14 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
err = -errno;
pr_warn("legacy kprobe perf_event_open() failed: %s\n",
libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
- return err;
+ goto clear_kprobe_event;
}
return pfd;
+
+clear_kprobe_event:
+ /* Clear the newly added kprobe_event */
+ remove_kprobe_event_legacy(probe_name, retprobe);
+ return err;
}
struct bpf_link *
--
2.34.1
Chuang W wrote:
> Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
> livepatch"), in a scenario where livepatch and kprobe coexist on the
> same function entry, the creation of kprobe_event using
> add_kprobe_event_legacy() will be successful, at the same time as a
> trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
> perf_event_open() will return an error because both livepatch and kprobe
> use FTRACE_OPS_FL_IPMODIFY.
>
> With this patch, whenever an error is returned after
> add_kprobe_event_legacy(), this ensures that the created kprobe_event is
> cleaned.
>
> Signed-off-by: Chuang W <[email protected]>
> Signed-off-by: Jingren Zhou <[email protected]>
> ---
> tools/lib/bpf/libbpf.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
I think we want to improve the commit message otherwise I'm sure we will
stumble on this in the future and from just above its tricky to follow.
I would suggest almost verbatim the description you gave in reply to
my question. Just cut'n'pasting your text together with minor edit
glue,
"
The legacy kprobe API (i.e. tracefs API) has two steps:
1) register_kprobe
$ echo 'p:mykprobe XXX' > /sys/kernel/debug/tracing/kprobe_events
This will create a trace event of mykprobe and register a disable
kprobe that waits to be activated.
2) enable_kprobe
2.1) using syscall perf_event_open as the following code,
perf_event_kprobe_open_legacy (file: tools/lib/bpf/libbpf.c):
---
attr.type = PERF_TYPE_TRACEPOINT;
pfd = syscall(__NR_perf_event_open, &attr,
pid < 0 ? -1 : pid, /* pid */
pid == -1 ? 0 : -1, /* cpu */
-1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
---
In the implementation code of perf_event_open, enable_kprobe() will be executed.
2.2) using shell
$ echo 1 > /sys/kernel/debug/tracing/events/kprobes/mykprobe/enable
As with perf_event_open, enable_kprobe() will also be executed.
When using the same function XXX, kprobe and livepatch cannot coexist,
that is, step 2) will return an error (ref: arm_kprobe_ftrace()),
however, step 1) is ok! The new kprobe API (i.e. perf kprobe API)
aggregates register_kprobe and enable_kprobe, internally fixes the
issue on failed enable_kprobe.
To fix: before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
livepatch"), in a scenario where livepatch and kprobe coexist on the
same function entry, the creation of kprobe_event using
add_kprobe_event_legacy() will be successful, at the same time as a
trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
perf_event_open() will return an error because both livepatch and kprobe
use FTRACE_OPS_FL_IPMODIFY.
With this patch, whenever an error is returned after
add_kprobe_event_legacy(), this ensures that the created kprobe_event is
cleaned.
"
Thanks,
John
On Tue, Jun 21, 2022 at 12:32 AM Chuang W <[email protected]> wrote:
>
> Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
> livepatch"), in a scenario where livepatch and kprobe coexist on the
> same function entry, the creation of kprobe_event using
> add_kprobe_event_legacy() will be successful, at the same time as a
> trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
> perf_event_open() will return an error because both livepatch and kprobe
> use FTRACE_OPS_FL_IPMODIFY.
>
> With this patch, whenever an error is returned after
> add_kprobe_event_legacy(), this ensures that the created kprobe_event is
> cleaned.
>
> Signed-off-by: Chuang W <[email protected]>
> Signed-off-by: Jingren Zhou <[email protected]>
> ---
This part is good, but I think there are few error paths in
bpf_program__attach_kprobe_opts() itself that would need to call
remove_kprobe_event_legacy() explicitly as well, no?
> tools/lib/bpf/libbpf.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 0781fae58a06..d0a36350e22a 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -10809,10 +10809,11 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
> }
> type = determine_kprobe_perf_type_legacy(probe_name, retprobe);
> if (type < 0) {
> + err = type;
> pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",
> kfunc_name, offset,
> - libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
> - return type;
> + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> + goto clear_kprobe_event;
> }
> attr.size = sizeof(attr);
> attr.config = type;
> @@ -10826,9 +10827,14 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
> err = -errno;
> pr_warn("legacy kprobe perf_event_open() failed: %s\n",
> libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> - return err;
> + goto clear_kprobe_event;
> }
> return pfd;
> +
> +clear_kprobe_event:
> + /* Clear the newly added kprobe_event */
> + remove_kprobe_event_legacy(probe_name, retprobe);
> + return err;
> }
>
> struct bpf_link *
> --
> 2.34.1
>
Hi, John. Thanks, I will resubmit V3 soon, and supplement the commit
information.
On Thu, Jun 23, 2022 at 11:37 AM John Fastabend
<[email protected]> wrote:
>
> Chuang W wrote:
> > Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
> > livepatch"), in a scenario where livepatch and kprobe coexist on the
> > same function entry, the creation of kprobe_event using
> > add_kprobe_event_legacy() will be successful, at the same time as a
> > trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
> > perf_event_open() will return an error because both livepatch and kprobe
> > use FTRACE_OPS_FL_IPMODIFY.
> >
> > With this patch, whenever an error is returned after
> > add_kprobe_event_legacy(), this ensures that the created kprobe_event is
> > cleaned.
> >
> > Signed-off-by: Chuang W <[email protected]>
> > Signed-off-by: Jingren Zhou <[email protected]>
> > ---
> > tools/lib/bpf/libbpf.c | 12 +++++++++---
> > 1 file changed, 9 insertions(+), 3 deletions(-)
>
> I think we want to improve the commit message otherwise I'm sure we will
> stumble on this in the future and from just above its tricky to follow.
> I would suggest almost verbatim the description you gave in reply to
> my question. Just cut'n'pasting your text together with minor edit
> glue,
>
> "
> The legacy kprobe API (i.e. tracefs API) has two steps:
>
> 1) register_kprobe
>
> $ echo 'p:mykprobe XXX' > /sys/kernel/debug/tracing/kprobe_events
>
> This will create a trace event of mykprobe and register a disable
> kprobe that waits to be activated.
>
> 2) enable_kprobe
>
> 2.1) using syscall perf_event_open as the following code,
> perf_event_kprobe_open_legacy (file: tools/lib/bpf/libbpf.c):
> ---
> attr.type = PERF_TYPE_TRACEPOINT;
> pfd = syscall(__NR_perf_event_open, &attr,
> pid < 0 ? -1 : pid, /* pid */
> pid == -1 ? 0 : -1, /* cpu */
> -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
> ---
>
> In the implementation code of perf_event_open, enable_kprobe() will be executed.
>
> 2.2) using shell
>
> $ echo 1 > /sys/kernel/debug/tracing/events/kprobes/mykprobe/enable
>
> As with perf_event_open, enable_kprobe() will also be executed.
>
> When using the same function XXX, kprobe and livepatch cannot coexist,
> that is, step 2) will return an error (ref: arm_kprobe_ftrace()),
> however, step 1) is ok! The new kprobe API (i.e. perf kprobe API)
> aggregates register_kprobe and enable_kprobe, internally fixes the
> issue on failed enable_kprobe.
>
> To fix: before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
> livepatch"), in a scenario where livepatch and kprobe coexist on the
> same function entry, the creation of kprobe_event using
> add_kprobe_event_legacy() will be successful, at the same time as a
> trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
> perf_event_open() will return an error because both livepatch and kprobe
> use FTRACE_OPS_FL_IPMODIFY.
>
> With this patch, whenever an error is returned after
> add_kprobe_event_legacy(), this ensures that the created kprobe_event is
> cleaned.
> "
>
> Thanks,
> John
Hi, Andrii,
Oh, yes. I verified that when bpf_program__attach_kprobe_opts() fails,
the kprobe_event did not clean up.
I will resubmit V3 soon, and fix it.
Thanks.
On Thu, Jun 23, 2022 at 12:03 PM Andrii Nakryiko
<[email protected]> wrote:
>
> On Tue, Jun 21, 2022 at 12:32 AM Chuang W <[email protected]> wrote:
> >
> > Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
> > livepatch"), in a scenario where livepatch and kprobe coexist on the
> > same function entry, the creation of kprobe_event using
> > add_kprobe_event_legacy() will be successful, at the same time as a
> > trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
> > perf_event_open() will return an error because both livepatch and kprobe
> > use FTRACE_OPS_FL_IPMODIFY.
> >
> > With this patch, whenever an error is returned after
> > add_kprobe_event_legacy(), this ensures that the created kprobe_event is
> > cleaned.
> >
> > Signed-off-by: Chuang W <[email protected]>
> > Signed-off-by: Jingren Zhou <[email protected]>
> > ---
>
> This part is good, but I think there are few error paths in
> bpf_program__attach_kprobe_opts() itself that would need to call
> remove_kprobe_event_legacy() explicitly as well, no?
>
> > tools/lib/bpf/libbpf.c | 12 +++++++++---
> > 1 file changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 0781fae58a06..d0a36350e22a 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -10809,10 +10809,11 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
> > }
> > type = determine_kprobe_perf_type_legacy(probe_name, retprobe);
> > if (type < 0) {
> > + err = type;
> > pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",
> > kfunc_name, offset,
> > - libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
> > - return type;
> > + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> > + goto clear_kprobe_event;
> > }
> > attr.size = sizeof(attr);
> > attr.config = type;
> > @@ -10826,9 +10827,14 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
> > err = -errno;
> > pr_warn("legacy kprobe perf_event_open() failed: %s\n",
> > libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> > - return err;
> > + goto clear_kprobe_event;
> > }
> > return pfd;
> > +
> > +clear_kprobe_event:
> > + /* Clear the newly added kprobe_event */
> > + remove_kprobe_event_legacy(probe_name, retprobe);
> > + return err;
> > }
> >
> > struct bpf_link *
> > --
> > 2.34.1
> >