Re: [PATCH bpf-next v2] bpf: Add bpf_check_attach_target_with_klog method to output failure logs to kernel
From: Yonghong Song
Date: Thu Jul 25 2024 - 02:10:14 EST
On 7/24/24 11:05 PM, Leon Hwang wrote:
On 25/7/24 13:54, Yonghong Song wrote:
On 7/24/24 10:15 PM, Zheao Li wrote:
This is a v2 patch, previous Link:
https://lore.kernel.org/bpf/20240724152521.20546-1-me@xxxxxxxxxxxx/T/#u
Compare with v1:
1. Format the code style and signed-off field
2. Use a shorter name bpf_check_attach_target_with_klog instead of
original name bpf_check_attach_target_with_kernel_log
When attaching a freplace hook, failures can occur,
but currently, no output is provided to help developers diagnose the
root cause.
This commit adds a new method, bpf_check_attach_target_with_klog,
which outputs the verifier log to the kernel.
Developers can then use dmesg to obtain more detailed information
about the failure.
For an example of eBPF code,
Link:
https://github.com/Asphaltt/learn-by-example/blob/main/ebpf/freplace/main.go
Co-developed-by: Leon Hwang <hffilwlqm@xxxxxxxxx>
Signed-off-by: Leon Hwang <hffilwlqm@xxxxxxxxx>
Signed-off-by: Zheao Li <me@xxxxxxxxxxxx>
---
include/linux/bpf_verifier.h | 5 +++++
kernel/bpf/syscall.c | 5 +++--
kernel/bpf/trampoline.c | 6 +++---
kernel/bpf/verifier.c | 19 +++++++++++++++++++
4 files changed, 30 insertions(+), 5 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 5cea15c81b8a..8eddba62c194 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -848,6 +848,11 @@ static inline void bpf_trampoline_unpack_key(u64
key, u32 *obj_id, u32 *btf_id)
*btf_id = key & 0x7FFFFFFF;
}
+int bpf_check_attach_target_with_klog(const struct bpf_prog *prog,
+ const struct bpf_prog *tgt_prog,
+ u32 btf_id,
+ struct bpf_attach_target_info *tgt_info);
format issue in the above. Same code alignment is needed for arguments
in different lines.
+
int bpf_check_attach_target(struct bpf_verifier_log *log,
const struct bpf_prog *prog,
const struct bpf_prog *tgt_prog,
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 869265852d51..bf826fcc8cf4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3464,8 +3464,9 @@ static int bpf_tracing_prog_attach(struct
bpf_prog *prog,
*/
struct bpf_attach_target_info tgt_info = {};
- err = bpf_check_attach_target(NULL, prog, tgt_prog, btf_id,
- &tgt_info);
+ err = bpf_check_attach_target_with_klog(prog, NULL,
+ prog->aux->attach_btf_id,
+ &tgt_info);
code alignment issue here as well.
Also, the argument should be 'prog, tgt_prog, btf_id, &tgt_info', right?
if (err)
goto out_unlock;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index f8302a5ca400..8862adaa7302 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -699,9 +699,9 @@ int bpf_trampoline_link_cgroup_shim(struct
bpf_prog *prog,
u64 key;
int err;
- err = bpf_check_attach_target(NULL, prog, NULL,
- prog->aux->attach_btf_id,
- &tgt_info);
+ err = bpf_check_attach_target_with_klog(prog, NULL,
+ prog->aux->attach_btf_id,
+ &tgt_info);
code alignment issue here
if (err)
return err;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1f5302fb0957..4873b72f5a9a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -21643,6 +21643,25 @@ static int
check_non_sleepable_error_inject(u32 btf_id)
return btf_id_set_contains(&btf_non_sleepable_error_inject,
btf_id);
}
+int bpf_check_attach_target_with_klog(const struct bpf_prog *prog,
+ const struct bpf_prog *tgt_prog,
+ u32 btf_id,
+ struct bpf_attach_target_info *tgt_info);
code alignment issue here.
+{
+ struct bpf_verifier_log *log;
+ int err;
+
+ log = kzalloc(sizeof(*log), GFP_KERNEL | __GFP_NOWARN);
__GFP_NOWARN is unnecessary here.
+ if (!log) {
+ err = -ENOMEM;
+ return err;
+ }
+ log->level = BPF_LOG_KERNEL;
+ err = bpf_check_attach_target(log, prog, tgt_prog, btf_id,
tgt_info);
+ kfree(log);
+ return err;
+}
+
int bpf_check_attach_target(struct bpf_verifier_log *log,
const struct bpf_prog *prog,
const struct bpf_prog *tgt_prog,
More importantly, Andrii has implemented retsnoop, which intends to locate
precise location in the kernel where err happens. The link is
https://github.com/anakryiko/retsnoop
Maybe you want to take a look and see whether it can resolve your issue.
We should really avoid putting more stuff in dmesg whenever possible.
retsnoop is really cool.
However, when something wrong in bpf_check_attach_target(), retsnoop
only gets its return value -EINVAL, without any bpf_log() in it. It's
hard to figure out the reason why bpf_check_attach_target() returns -EINVAL.
It should have line number like below in https://github.com/anakryiko/retsnoop
|$ sudo ./retsnoop -e '*sys_bpf' -a ':kernel/bpf/*.c' Receiving data...
20:19:36.372607 -> 20:19:36.372682 TID/PID 8346/8346 (simfail/simfail):
entry_SYSCALL_64_after_hwframe+0x63 (arch/x86/entry/entry_64.S:120:0)
do_syscall_64+0x35 (arch/x86/entry/common.c:80:7) . do_syscall_x64
(arch/x86/entry/common.c:50:12) 73us [-ENOMEM] __x64_sys_bpf+0x1a
(kernel/bpf/syscall.c:5067:1) 70us [-ENOMEM] __sys_bpf+0x38b
(kernel/bpf/syscall.c:4947:9) . map_create (kernel/bpf/syscall.c:1106:8)
. find_and_alloc_map (kernel/bpf/syscall.c:132:5) ! 50us [-ENOMEM]
array_map_alloc !* 2us [NULL] bpf_map_alloc_percpu Could you double
check? It does need corresponding kernel source though. |
How about adding a tracepoint in bpf_check_attach_target_with_klog()?
It's to avoid putting stuff in dmesg.
Thanks,
Leon