Re: [PATCH bpf-next v5 4/9] bpf: Add syscall common attributes support for prog_load

[Andrii Nakryiko]

On Mon, Jan 12, 2026 at 6:59 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>
> The log buffer of common attributes would be confusing with the one in
> 'union bpf_attr' for BPF_PROG_LOAD.
>
> In order to clarify the usage of these two log buffers, they both can be
> used for logging if:
>
> * They are same, including 'log_buf', 'log_level' and 'log_size'.
> * One of them is missing, then another one will be used for logging.
>
> If they both have 'log_buf' but they are not same totally, return -EUSERS.

why use this special error code that we don't seem to use in BPF
subsystem at all? What's wrong with -EINVAL. This shouldn't be an easy
mistake to do, tbh.

>
> Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
> ---
>  include/linux/bpf_verifier.h |  4 +++-
>  kernel/bpf/log.c             | 29 ++++++++++++++++++++++++++---
>  kernel/bpf/syscall.c         |  9 ++++++---
>  3 files changed, 35 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 4c9632c40059..da2d37ca60e7 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -637,9 +637,11 @@ struct bpf_log_attr {
>         u32 log_level;
>         struct bpf_attrs *attrs;
>         u32 offsetof_log_true_size;
> +       struct bpf_attrs *attrs_common;
>  };
>
> -int bpf_prog_load_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs);
> +int bpf_prog_load_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs,
> +                               struct bpf_attrs *attrs_common);
>  int bpf_log_attr_finalize(struct bpf_log_attr *log_attr, struct bpf_verifier_log *log);
>
>  #define BPF_MAX_SUBPROGS 256
> diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
> index 457b724c4176..eba60a13e244 100644
> --- a/kernel/bpf/log.c
> +++ b/kernel/bpf/log.c
> @@ -865,23 +865,41 @@ void print_insn_state(struct bpf_verifier_env *env, const struct bpf_verifier_st
>  }
>
>  static int bpf_log_attr_init(struct bpf_log_attr *log_attr, struct bpf_attrs *attrs, u64 log_buf,
> -                            u32 log_size, u32 log_level, int offsetof_log_true_size)
> +                            u32 log_size, u32 log_level, int offsetof_log_true_size,
> +                            struct bpf_attrs *attrs_common)
>  {
> +       const struct bpf_common_attr *common_attr = attrs_common ? attrs_common->attr : NULL;
> +

There is something to be said about naming choices here :) it's easy
to get lost in attrs_common being actually bpf_attrs, which contains
attr field, which is actually of bpf_common_attr type... It's a bit
disorienting. :)

>         memset(log_attr, 0, sizeof(*log_attr));
>         log_attr->log_buf = log_buf;
>         log_attr->log_size = log_size;
>         log_attr->log_level = log_level;
>         log_attr->attrs = attrs;
>         log_attr->offsetof_log_true_size = offsetof_log_true_size;
> +       log_attr->attrs_common = attrs_common;
> +
> +       if (log_buf && common_attr && common_attr->log_buf &&
> +               (log_buf != common_attr->log_buf ||
> +                log_size != common_attr->log_size ||
> +                log_level != common_attr->log_level))
> +               return -EUSERS;
> +
> +       if (!log_buf && common_attr && common_attr->log_buf) {
> +               log_attr->log_buf = common_attr->log_buf;
> +               log_attr->log_size = common_attr->log_size;
> +               log_attr->log_level = common_attr->log_level;
> +       }
> +
>         return 0;
>  }
>

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