linux-kernel - Re: [RFC PATCH net-next 3/5] bpf/verifier: feed pointer-to-unknown-scalar casts into scalar ALU path

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Message-ID: <20170608165004.n5jc33pocxlytuvf@ast-mbp.dhcp.thefacebook.com>
Date:   Thu, 8 Jun 2017 09:50:06 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Edward Cree <ecree@...arflare.com>
Cc:     davem@...emloft.net, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        iovisor-dev <iovisor-dev@...ts.iovisor.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH net-next 3/5] bpf/verifier: feed
 pointer-to-unknown-scalar casts into scalar ALU path

On Thu, Jun 08, 2017 at 04:25:39PM +0100, Edward Cree wrote:
> On 08/06/17 03:35, Alexei Starovoitov wrote:
> > such large back and forth move doesn't help reviewing.
> > may be just merge it into previous patch?
> > Or keep that function in the right place in patch 2 already?
> I think 'diff' got a bit confused, and maybe with different options I could
>  have got it to produce something more readable.  But I think I will just
>  merge this into patch 2; it's only separate because it started out as an
>  experiment.

after sleeping on it I'm not sure we should be allowing such pointer
arithmetic. In normal C code people do fancy tricks with lower 3 bits
of the pointer, but in bpf code I cannot see such use case.
What kind of realistic code will be doing ptr & 0x40 ?