netdev - Re: [PATCH] ppc: Fix BPF JIT for ABIv2

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Date:	Tue, 21 Jun 2016 08:45:59 -0700
From:	Alexei Starovoitov <ast@...com>
To:	Thadeu Lima de Souza Cascardo <cascardo@...hat.com>,
	Michael Ellerman <mpe@...erman.id.au>
CC:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
	<linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<netdev@...r.kernel.org>, Matt Evans <matt@...abs.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Denis Kirjanov <kda@...ux-powerpc.org>,
	"Paul Mackerras" <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>,
	"Ananth N Mavinakayanahalli" <ananth@...ibm.com>
Subject: Re: [PATCH] ppc: Fix BPF JIT for ABIv2

On 6/21/16 7:47 AM, Thadeu Lima de Souza Cascardo wrote:
>>>
>>> The calling convention is different with ABIv2 and so we'll need changes
>>> in bpf_slow_path_common() and sk_negative_common().
>>
>> How big would those changes be? Do we know?
>>
>> How come no one reported this was broken previously? This is the first I've
>> heard of it being broken.
>>
>
> I just heard of it less than two weeks ago, and only could investigate it last
> week, when I realized mainline was also affected.
>
> It looks like the little-endian support for classic JIT were done before the
> conversion to ABIv2. And as JIT is disabled by default, no one seems to have
> exercised it.

it's not a surprise unfortunately. The JITs that were written before
test_bpf.ko was developed were missing corner cases. Typical tcpdump
would be fine, but fragmented packets, negative offsets and
out-out-bounds wouldn't be handled correctly.
I'd suggest to validate the stable backport with test_bpf as well.