netdev - Re: [PATCH net] bpf: enforce correct alignment for instructions

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Date:   Thu, 21 Jun 2018 23:03:09 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>, edumazet@...gle.com
Cc:     netdev@...r.kernel.org, kafai@...com, ast@...nel.org
Subject: Re: [PATCH net] bpf: enforce correct alignment for instructions

On 06/21/2018 06:08 AM, Eric Dumazet wrote:
> On 06/20/2018 08:46 PM, David Miller wrote:
>> From: Eric Dumazet <edumazet@...gle.com>
>> Date: Wed, 20 Jun 2018 17:24:09 -0700
>>
>>> After commit 9facc336876f ("bpf: reject any prog that failed read-only lock")
>>> offsetof(struct bpf_binary_header, image) became 3 instead of 4,
>>> breaking powerpc BPF badly, since instructions need to be word aligned.
>>>
>>> Fixes: 9facc336876f ("bpf: reject any prog that failed read-only lock")
>>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>>
>> I'll apply this directly, thanks Eric.
> 
> Thanks David :)

Sigh, sorry for the breakage, looks like I got fooled by x86 gcc.

struct bpf_binary_header {
        u16                        pages;                /*     0     2 */
        u16                        locked:1;             /*     2:15  2 */

        /* XXX 15 bits hole, try to pack */

        u8                         image[0];             /*     4     0 */

        /* size: 4, cachelines: 1, members: 3 */
        /* bit holes: 1, sum bit holes: 15 bits */
        /* last cacheline: 4 bytes */
};

Thanks Eric!