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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Fri, 10 Jun 2022 16:56:54 -0700
Message-ID: <CAADnVQLL_5NHxNJytDrZCKkQpHx6zLTJYVFzYwPxyWVJZHE-FQ@mail.gmail.com>
Subject: Re: [PATCH v3 1/2] bpf: Add bpf_verify_signature() helper
To:     KP Singh <kpsingh@kernel.org>
Cc:     Daniel Borkmann <daniel@iogearbox.net>,
        Roberto Sassu <roberto.sassu@huawei.com>,
        "ast@kernel.org" <ast@kernel.org>,
        "andrii@kernel.org" <andrii@kernel.org>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        kernel test robot <lkp@intel.com>,
        "john.fastabend@gmail.com" <john.fastabend@gmail.com>
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On Fri, Jun 10, 2022 at 4:53 PM KP Singh <kpsingh@kernel.org> wrote:
> > >>> +static const struct bpf_func_proto bpf_verify_signature_proto = {
> > >>> +   .func           = bpf_verify_signature,
> > >>> +   .gpl_only       = false,
> > >>> +   .ret_type       = RET_INTEGER,
> > >>> +   .arg1_type      = ARG_PTR_TO_MEM,
> > >>> +   .arg2_type      = ARG_CONST_SIZE_OR_ZERO,
> > >>
> > >> Can verify_pkcs7_signature() handle null/0 len for data* args?
> > >
> > > Shouldn't ARG_PTR_TO_MEM require valid memory? 0 len should
> > > not be a problem.
> >
> > check_helper_mem_access() has:
> >
> >       /* Allow zero-byte read from NULL, regardless of pointer type */
> >       if (zero_size_allowed && access_size == 0 &&
> >           register_is_null(reg))
> >               return 0;
>
> Daniel, makes a fair point here. Alexei, what do you think?
>
> I wonder if some "future" signature verification would need even more
> / different arguments so a unified bpf_verify_signature might get more
> complex / not easy to extend.

You mean a pkcs7 specific helper for now?
Makes sense.