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

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Date:   Mon, 14 Sep 2020 18:12:34 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Will Deacon <will@...nel.org>
Cc:     brouer@...hat.com, Ilias Apalodimas <ilias.apalodimas@...aro.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@...r.kernel.org,
        Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH] arm64: bpf: Fix branch offset in JIT


On Mon, 14 Sep 2020 15:01:15 +0100 Will Deacon <will@...nel.org> wrote:

> Hi Ilias,
> 
> On Mon, Sep 14, 2020 at 04:23:50PM +0300, Ilias Apalodimas wrote:
> > On Mon, Sep 14, 2020 at 03:35:04PM +0300, Ilias Apalodimas wrote:  
> > > On Mon, Sep 14, 2020 at 01:20:43PM +0100, Will Deacon wrote:  
> > > > On Mon, Sep 14, 2020 at 11:36:21AM +0300, Ilias Apalodimas wrote:  
> > > > > Running the eBPF test_verifier leads to random errors looking like this:  
> 
> [...]
> > >   
> > Any suggestion on any Fixes I should apply? The original code was 'correct' and
> > broke only when bounded loops and their self-tests were introduced.  
> 
> Ouch, that's pretty bad as it means nobody is regression testing BPF on
> arm64 with mainline. Damn.

Yes, it unfortunately seems that upstream is lacking BPF regression
testing for ARM64 :-(

This bug surfaced when Red Hat QA tested our kernel backports, on
different archs.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer