linux-kernel - Re: [PATCH 1/6] ebpf: add a seccomp program type

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Date:	Wed, 9 Sep 2015 09:37:51 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Tycho Andersen <tycho.andersen@...onical.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Will Drewry <wad@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/6] ebpf: add a seccomp program type

On Wed, Sep 9, 2015 at 9:09 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
> On 09/09/2015 06:07 PM, Alexei Starovoitov wrote:
>>
>> On Wed, Sep 09, 2015 at 09:50:35AM -0600, Tycho Andersen wrote:
>
> [...]
>>>
>>> Thoughts?
>>
>>
>> Please do not add any per-instruction hacks. None of them are
>> necessary. Classic had to do extra ugly checks in seccomp only
>> because verifier wasn't flexible enough.
>> If you don't want to see any BPF_CALL in seccomp, just have
>> empty get_func_proto() callback for BPF_PROG_TYPE_SECCOMP
>> and verifier will reject all calls.
>> Currently we have only two non-generic instrucitons
>> LD_ABS and LD_IND that are avaialable for sockets/TC only,
>> because these are legacy instructions and we had to make
>> exceptions for them.
>
> Yep, +1.

Hrmpf. This adds to the cognitive load for accepting this patch
series. :P Now I have to convince myself that there is no additional
exposure to seccomp by using the entire set of eBPF instructions.
While I'm pretty sure it'll be fine, I really don't want to risk being
wrong and opening a hole here. I will spend some time looking at the
new eBPF instructions...

-Kees

-- 
Kees Cook
Chrome OS Security
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