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Message-ID: <CAEf4Bzb-b+EcF1oLXA7mijL5kVmjpOuh2B+LPM9x4tAFOYHCsw@mail.gmail.com>
Date: Wed, 11 Feb 2026 14:10:06 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Leon Hwang <leon.hwang@...ux.dev>
Cc: bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>,
Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,
Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Shuah Khan <shuah@...nel.org>, Christian Brauner <brauner@...nel.org>,
Seth Forshee <sforshee@...nel.org>, Yuichiro Tsuji <yuichtsu@...zon.com>,
Andrey Albershteyn <aalbersh@...hat.com>, Willem de Bruijn <willemb@...gle.com>,
Jason Xing <kerneljasonxing@...il.com>, Tao Chen <chen.dylane@...ux.dev>,
Mykyta Yatsenko <yatsenko@...a.com>, Kumar Kartikeya Dwivedi <memxor@...il.com>,
Anton Protopopov <a.s.protopopov@...il.com>, Amery Hung <ameryhung@...il.com>,
Rong Tao <rongtao@...tc.cn>, linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
linux-kselftest@...r.kernel.org, kernel-patches-bot@...com
Subject: Re: [PATCH bpf-next v10 3/8] bpf: Refactor reporting log_true_size
for prog_load
On Wed, Feb 11, 2026 at 7:13 AM Leon Hwang <leon.hwang@...ux.dev> wrote:
>
> The next commit will add support for reporting logs via extended common
> attributes, including 'log_true_size'.
>
> To prepare for that, refactor the 'log_true_size' reporting logic by
> introducing a new struct bpf_log_attr to encapsulate log-related behavior:
>
> * bpf_log_attr_init(): initialize log fields, which will support
> extended common attributes in the next commit.
> * bpf_log_attr_finalize(): handle log finalization and write back
> 'log_true_size' to userspace.
>
> Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
> ---
> include/linux/bpf.h | 4 +++-
> include/linux/bpf_verifier.h | 11 +++++++++++
> kernel/bpf/log.c | 25 +++++++++++++++++++++++++
> kernel/bpf/syscall.c | 13 ++++++++++---
> kernel/bpf/verifier.c | 17 ++++-------------
> 5 files changed, 53 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index cd9b96434904..d4dbcc7ad156 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2913,7 +2913,9 @@ int bpf_check_uarg_tail_zero(bpfptr_t uaddr, size_t expected_size,
> size_t actual_size);
>
> /* verify correctness of eBPF program */
> -int bpf_check(struct bpf_prog **fp, union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size);
> +struct bpf_log_attr;
> +int bpf_check(struct bpf_prog **fp, union bpf_attr *attr, bpfptr_t uattr,
> + struct bpf_log_attr *attr_log);
>
> #ifndef CONFIG_BPF_JIT_ALWAYS_ON
> void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth);
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index ef8e45a362d9..dbd9bdb955b3 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -635,6 +635,17 @@ static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log)
> return log && log->level;
> }
>
> +struct bpf_log_attr {
> + char __user *log_buf;
> + u32 log_size;
> + u32 log_level;
> + u32 __user *log_true_size;
> +};
> +
> +int bpf_log_attr_init(struct bpf_log_attr *log, u64 log_buf, u32 log_size, u32 log_level,
> + u32 __user *log_true_size);
> +int bpf_log_attr_finalize(struct bpf_log_attr *attr, struct bpf_verifier_log *log);
> +
> #define BPF_MAX_SUBPROGS 256
>
> struct bpf_subprog_arg_info {
> diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
> index a0c3b35de2ce..e31747b84fe2 100644
> --- a/kernel/bpf/log.c
> +++ b/kernel/bpf/log.c
> @@ -863,3 +863,28 @@ void print_insn_state(struct bpf_verifier_env *env, const struct bpf_verifier_st
> }
> print_verifier_state(env, vstate, frameno, false);
> }
> +
> +int bpf_log_attr_init(struct bpf_log_attr *log, u64 log_buf, u32 log_size, u32 log_level,
> + u32 __user *log_true_size)
> +{
> + memset(log, 0, sizeof(*log));
> + log->log_buf = u64_to_user_ptr(log_buf);
> + log->log_size = log_size;
> + log->log_level = log_level;
> + log->log_true_size = log_true_size;
> + return 0;
> +}
> +
> +int bpf_log_attr_finalize(struct bpf_log_attr *attr, struct bpf_verifier_log *log)
> +{
> + u32 log_true_size;
> + int err;
> +
> + err = bpf_vlog_finalize(log, &log_true_size);
> +
> + if (attr->log_true_size && copy_to_user(attr->log_true_size, &log_true_size,
> + sizeof(log_true_size)))
> + return -EFAULT;
> +
> + return err;
> +}
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 0e231c0b1d04..e86674811996 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2867,7 +2867,7 @@ static int bpf_prog_mark_insn_arrays_ready(struct bpf_prog *prog)
> /* last field in 'union bpf_attr' used by this command */
> #define BPF_PROG_LOAD_LAST_FIELD keyring_id
>
> -static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
> +static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, struct bpf_log_attr *attr_log)
> {
> enum bpf_prog_type type = attr->prog_type;
> struct bpf_prog *prog, *dst_prog = NULL;
> @@ -3085,7 +3085,7 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
> goto free_prog_sec;
>
> /* run eBPF verifier */
> - err = bpf_check(&prog, attr, uattr, uattr_size);
> + err = bpf_check(&prog, attr, uattr, attr_log);
> if (err < 0)
> goto free_used_maps;
>
> @@ -6189,7 +6189,10 @@ static int prog_assoc_struct_ops(union bpf_attr *attr)
> static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
> bpfptr_t uattr_common, unsigned int size_common)
> {
> + bool from_user = !bpfptr_is_kernel(uattr);
> struct bpf_common_attr attr_common;
> + u32 __user *log_true_size = NULL;
> + struct bpf_log_attr attr_log;
> union bpf_attr attr;
> int err;
>
> @@ -6241,7 +6244,11 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
> err = map_freeze(&attr);
> break;
> case BPF_PROG_LOAD:
> - err = bpf_prog_load(&attr, uattr, size);
> + if (from_user && size >= offsetofend(union bpf_attr, log_true_size))
> + log_true_size = uattr.user + offsetof(union bpf_attr, log_true_size);
LGTM, so
Acked-by: Andrii Nakryiko <andrii@...nel.org>
but it caught my eye that we will never return log_true_size if
SYSCALL program tried to load another BPF program (light skeleton
case), which seems limiting, but we can perhaps address that
separately as a follow up
> + err = bpf_log_attr_init(&attr_log, attr.log_buf, attr.log_size, attr.log_level,
> + log_true_size);
> + err = err ?: bpf_prog_load(&attr, uattr, &attr_log);
> break;
> case BPF_OBJ_PIN:
> err = bpf_obj_pin(&attr);
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index edf5342b982f..f1447b1878fd 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -25840,12 +25840,12 @@ static int compute_scc(struct bpf_verifier_env *env)
> return err;
> }
>
> -int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u32 uattr_size)
> +int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
> + struct bpf_log_attr *attr_log)
> {
> u64 start_time = ktime_get_ns();
> struct bpf_verifier_env *env;
> int i, len, ret = -EINVAL, err;
> - u32 log_true_size;
> bool is_priv;
>
> BTF_TYPE_EMIT(enum bpf_features);
> @@ -25892,9 +25892,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
> /* user could have requested verbose verifier output
> * and supplied buffer to store the verification trace
> */
> - ret = bpf_vlog_init(&env->log, attr->log_level,
> - (char __user *) (unsigned long) attr->log_buf,
> - attr->log_size);
> + ret = bpf_vlog_init(&env->log, attr_log->log_level, attr_log->log_buf, attr_log->log_size);
> if (ret)
> goto err_unlock;
>
> @@ -26044,17 +26042,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
> env->prog->aux->verified_insns = env->insn_processed;
>
> /* preserve original error even if log finalization is successful */
> - err = bpf_vlog_finalize(&env->log, &log_true_size);
> + err = bpf_log_attr_finalize(attr_log, &env->log);
> if (err)
> ret = err;
>
> - if (uattr_size >= offsetofend(union bpf_attr, log_true_size) &&
> - copy_to_bpfptr_offset(uattr, offsetof(union bpf_attr, log_true_size),
> - &log_true_size, sizeof(log_true_size))) {
> - ret = -EFAULT;
> - goto err_release_maps;
> - }
> -
> if (ret)
> goto err_release_maps;
>
> --
> 2.52.0
>
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