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Date:   Tue, 3 Mar 2020 16:03:27 -0800
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
To:     KP Singh <kpsingh@chromium.org>
Cc:     Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        open list <linux-kernel@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Paul Turner <pjt@google.com>,
        Florent Revest <revest@chromium.org>,
        Brendan Jackman <jackmanb@chromium.org>
Subject: Re: [PATCH bpf-next 4/7] bpf: Attachment verification for
 BPF_MODIFY_RETURN
Message-ID: <20200304000326.nk7jmkgxazl3umbh@ast-mbp>
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 <CAEf4BzaviDB+WGUsg1+aO5GAtkJuQ6aYSiB8VaKL0CoQRPs8Xw@mail.gmail.com>
 <20200303232151.GB17103@chromium.org>
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On Wed, Mar 04, 2020 at 12:21:51AM +0100, KP Singh wrote:
> 
> > > +                       t = btf_type_skip_modifiers(btf, t->type, NULL);
> > > +                       if (!btf_type_is_int(t)) {
> > 
> > Should the size of int be verified here? E.g., if some function
> > returns u8, is that ok for BPF program to return, say, (1<<30) ?
> 
> Would this work?
> 
>        if (size != t->size) {
>                bpf_log(log,
>                        "size accessed = %d should be %d\n",
>                        size, t->size);
>                return false;
>        }

It will cause spurious failures later when llvm optimizes
if (ret & 0xff) into u8 load.
I think btf_type_is_int() is enough as-is.