netdev - Re: [PATCH bpf-next] bpf/verifier: enable ctx + const + 0.

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Date:   Wed, 2 May 2018 13:51:36 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     William Tu <u9012063@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Yonghong Song <yhs@...com>, Yifeng Sun <pkusunyifeng@...il.com>
Subject: Re: [PATCH bpf-next] bpf/verifier: enable ctx + const + 0.

On Wed, 2 May 2018 10:54:56 -0700, William Tu wrote:
> On Wed, May 2, 2018 at 1:29 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
> > On 05/02/2018 06:52 AM, Alexei Starovoitov wrote:  
> >> On Tue, May 01, 2018 at 09:35:29PM -0700, William Tu wrote:  
> >> Please test it with real program and you'll see crashes and garbage returned.  
> >
> > +1, *convert_ctx_access() use bpf_insn's off to determine what to rewrite,
> > so this is definitely buggy, and wasn't properly tested as it should have
> > been. The test case is also way too simple, just the LDX and then doing a
> > return 0 will get you past verifier, but won't give you anything in terms
> > of runtime testing that test_verifier is doing. A single test case for a
> > non trivial verifier change like this is also _completely insufficient_,
> > this really needs to test all sort of weird corner cases (involving out of
> > bounds accesses, overflows, etc).  
> 
> Thanks, now I understand.
> It's much more complicated than I thought.

FWIW NFP JIT would also have to be updated, similarly to
*convert_ctx_access() in mem_ldx_skb()/mem_ldx_xdp() we are currently
looking at insn.off.  In case you find a way to solve this.. :)