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

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Message-Id: <20180622.071010.933545844318467100.davem@davemloft.net>
Date:   Fri, 22 Jun 2018 07:10:10 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     daniel@...earbox.net
Cc:     eric.dumazet@...il.com, edumazet@...gle.com,
        netdev@...r.kernel.org, kafai@...com, ast@...nel.org
Subject: Re: [PATCH net] bpf: enforce correct alignment for instructions

From: Daniel Borkmann <daniel@...earbox.net>
Date: Thu, 21 Jun 2018 23:03:09 +0200

> 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 */

Note that you can also just make locked a plan u16 for now until you
need more flag bits, the code generated will be more efficient
especially on non-x86.