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

[Leon Hwang <leon.hwang@linux.dev>]

On 5/2/26 03:48, Andrii Nakryiko wrote:
> On Mon, Feb 2, 2026 at 6:42 AM Leon Hwang <leon.hwang@linux.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_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@linux.dev>
>> ---
>>  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?
> 

In patch #7, 'log' can be NULL when users do not provide 'log_buf'.

However, bpf_vlog_finalize() already guards against this case, so I'll
drop this check.

>> +
>> +       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;
> 

Ack.

Thanks,
Leon