Re: [PATCH v2 bpf-next 2/6] bpf: remove minimum size restrictions on verifier log buffer

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Mar 30, 2023 at 10:12 AM Lorenz Bauer <lmb@isovalent.com> wrote:
>
> On Wed, Mar 29, 2023 at 12:56 AM Andrii Nakryiko <andrii@kernel.org> wrote:
> >
> > It's not clear why we have 128 as minimum size, but it makes testing
> > harder and seems unnecessary, as we carefully handle truncation
> > scenarios and use proper snprintf variants. So remove this limitation
> > and just enfore positive length for log buffer.
>
> Nit: enforce

life is boring without typos, will fix in the next revision (if there
has to be another one) :)

>
> >
> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
>
> Acked-by: Lorenz Bauer <lmb@isovalent.com>
>
> > ---
> >  kernel/bpf/log.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
> > index 920061e38d2e..1974891fc324 100644
> > --- a/kernel/bpf/log.c
> > +++ b/kernel/bpf/log.c
> > @@ -11,7 +11,7 @@
> >
> >  bool bpf_verifier_log_attr_valid(const struct bpf_verifier_log *log)
> >  {
> > -       return log->len_total >= 128 && log->len_total <= UINT_MAX >> 2 &&
> > +       return log->len_total > 0 && log->len_total <= UINT_MAX >> 2 &&
> >                log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK);
>
> Probably discussion for your second series. Thought experiment, could
> this be len_total >= 0? I'm still after a way to get the correct log
> buffer size from the first PROG_LOAD call. If the kernel could handle
> this I could mmap a PROT_NONE page, set len_total to 0 and later read
> out the correct buffer size.
>
> I'm guessing that the null termination logic would have to be
> adjusted, anything else though?

I haven't tried, but I'll check if anything needs to be adjusted. But
I don't mind this semantics, it matches other places, like when
getting JIT dump for program info, etc.