Re: [PATCH bpf-next v9 3/9] bpf: Refactor reporting log_true_size for prog_load

[Andrii Nakryiko]

On Mon, Feb 2, 2026 at 6:42 AM Leon Hwang <leon.hwang@xxxxxxxxx> 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_prog_load_log_attr_init(): initialize the 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@xxxxxxxxx>
> ---
>  include/linux/bpf.h          |  4 +++-
>  include/linux/bpf_verifier.h | 10 ++++++++++
>  kernel/bpf/log.c             | 35 +++++++++++++++++++++++++++++++++++
>  kernel/bpf/syscall.c         |  8 +++++---
>  kernel/bpf/verifier.c        | 13 +++----------
>  5 files changed, 56 insertions(+), 14 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 8355b585cd18..c805b85b6f7a 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -631,6 +631,16 @@ static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log)
>         return log && log->level;
>  }
>
> +struct bpf_log_attr {
> +       u32 offsetof_true_size;
> +       u32 uattr_size;
> +       bpfptr_t uattr;
> +};
> +
> +int bpf_prog_load_log_attr_init(struct bpf_log_attr *attr_log, union bpf_attr *attr,
> +                               bpfptr_t uattr, u32 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..ff579fcba36f 100644
> --- a/kernel/bpf/log.c
> +++ b/kernel/bpf/log.c
> @@ -863,3 +863,38 @@ void print_insn_state(struct bpf_verifier_env *env, const struct bpf_verifier_st
>         }
>         print_verifier_state(env, vstate, frameno, false);
>  }
> +
> +static void bpf_log_attr_init(struct bpf_log_attr *attr_log, int offsetof_true_size, bpfptr_t uattr,
> +                             u32 uattr_size)
> +{
> +       memset(attr_log, 0, sizeof(*attr_log));
> +       attr_log->offsetof_true_size = offsetof_true_size;
> +       attr_log->uattr_size = uattr_size;
> +       attr_log->uattr = uattr;
> +}
> +
> +int bpf_prog_load_log_attr_init(struct bpf_log_attr *attr_log, union bpf_attr *attr,
> +                               bpfptr_t uattr, u32 size)
> +{
> +       bpf_log_attr_init(attr_log, offsetof(union bpf_attr, log_true_size), uattr, size);
> +       return 0;
> +}
> +
> +int bpf_log_attr_finalize(struct bpf_log_attr *attr, struct bpf_verifier_log *log)
> +{
> +       u32 log_true_size;
> +       size_t size;
> +       int err;
> +
> +       if (!log)
> +               return 0;

can this ever happen? why guard against this?

> +
> +       err = bpf_vlog_finalize(log, &log_true_size);
> +
> +       size = sizeof(log_true_size);
> +       if (attr->uattr_size >= attr->offsetof_true_size + size &&
> +           copy_to_bpfptr_offset(attr->uattr, attr->offsetof_true_size, &log_true_size, size))
> +               err = -EFAULT;

minor nit: return -EFAULT;

> +
> +       return err;
> +}

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