netdev - Re: [PATCH net] ebpf, x86: fix general protection fault when tail call is invoked

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Date:	Tue, 28 Jul 2015 19:17:11 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Alexei Starovoitov <ast@...mgrid.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net] ebpf, x86: fix general protection fault when tail
 call is invoked

On 07/28/2015 07:02 PM, Alexei Starovoitov wrote:
> On 7/28/15 6:26 AM, Daniel Borkmann wrote:
>> After patch, disassembly:
>>
>>    [...]
>>    9e:   lea    0x80(%rsi,%rdx,8),%rax   <--- CONFIG_LOCKDEP/CONFIG_LOCK_STAT
>>          48 8d 84 d6 80 00 00 00
>>    a6:   mov    (%rax),%rax
>>          48 8b 00
>>    [...]
>>
>>    [...]
>>    9e:   lea    0x50(%rsi,%rdx,8),%rax   <--- No CONFIG_LOCKDEP
>>          48 8d 84 d6 50 00 00 00
>>    a6:   mov    (%rax),%rax
>>          48 8b 00
>>    [...]
>>
>> Fixes: b52f00e6a715 ("x86: bpf_jit: implement bpf_tail_call() helper")
>> Signed-off-by: Daniel Borkmann<daniel@...earbox.net>
>
> Thanks for fixing it.

No problem!

> Most of my development is actually with LOCKDEP on, but I don't ever
> turn LOCK_STAT on, so sadly missed this 48 byte increase of 80 byte
> structure :(

I feel that at some point we might have hit this anyway, e.g. Huawei
guys with their perf work further extending bpf_maps, etc, etc.

Thanks,
Daniel
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