netdev - Re: UBSAN: array-index-out-of-bounds in kernel/bpf/arraymap.c:177

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Date:   Tue, 19 May 2020 21:55:45 -0400
From:   Qian Cai <cai@....pw>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Linux Netdev List <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: UBSAN: array-index-out-of-bounds in kernel/bpf/arraymap.c:177



> On May 19, 2020, at 7:23 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> 
> I agree, it's bad to have this noise. But again, there is nothing
> wrong with the way it's used in BPF code base. We'd gladly use
> flexible array, if we could. But given we can't, I'd say the proper
> solution (in order of my preference) would be:
> 
>  - don't trigger false error, if zero-sized array is the member of union;
>  - or have some sort of annotation at field declaration site (not a
> field access site).
> 
> Is that possible?

I am not a compiler expert, but with my experience with all those compiler instrumental technology like KCSAN, KASAN and UBSAN, it seems both options you prop need to modify compilers, i.e., -fsanitize=undefined