netdev - Re: [PATCH] arm64: bpf: Fix branch offset in JIT

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Date:   Mon, 14 Sep 2020 20:55:16 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Xi Wang <xi.wang@...il.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Will Deacon <will@...nel.org>, bpf@...r.kernel.org,
        ardb@...nel.org, naresh.kamboju@...aro.org,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Yauheni Kaliuta <yauheni.kaliuta@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        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>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH] arm64: bpf: Fix branch offset in JIT

On Mon, Sep 14, 2020 at 10:47:33AM -0700, Xi Wang wrote:
> On Mon, Sep 14, 2020 at 10:03 AM Ilias Apalodimas
> <ilias.apalodimas@...aro.org> wrote:
> > Naresh from Linaro reported it during his tests on 5.8-rc1 as well [1].
> > I've included both Jiri and him on the v2 as reporters.
> >
> > [1] https://lkml.org/lkml/2020/8/11/58
> 
> I'm curious what you think of Luke's earlier patch to this bug:

We've briefly discussed this approach with Yauheni while coming up with the 
posted patch.
I think that contructing the array correctly in the first place is better. 
Right now it might only be used in bpf2a64_offset() and bpf_prog_fill_jited_linfo()
but if we fixup the values on the fly in there, everyone that intends to use the
offset for any reason will have to account for the missing instruction.

Cheers
/Ilias
> 
> https://lore.kernel.org/bpf/CANoWswkaj1HysW3BxBMG9_nd48fm0MxM5egdtmHU6YsEc_GUtQ@mail.gmail.com/T/#m4335b4005da0d60059ba96920fcaaecf2637042a