linux-kernel - Re: [PATCH v13 net-next 07/11] bpf: verifier (add ability to receive verification log)

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Date:	Thu, 18 Sep 2014 16:50:04 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v13 net-next 07/11] bpf: verifier (add ability to receive
 verification log)

On 09/18/2014 04:34 PM, Alexei Starovoitov wrote:
> On Wed, Sep 17, 2014 at 11:44 PM, Daniel Borkmann <dborkman@...hat.com> wrote:
...
>> Sure, you will never get a full compatibility on that regard
>> while backwards compatibility needs to be guaranteed on the
>> other hand. I looked at perf_copy_attr() implementation and I
>> think that we should mimic it in a very similar way as it
>> exactly solves what we need.
>>
>> For example, it will return with -EINVAL for (size > PAGE_SIZE)
>> and (size < PERF_ATTR_SIZE_VER0) where PAGE_SIZE has been chosen
>> as an arbitrary hard upper limit where it is believed that it will
>> never grow beyond that large limit in future.
>>
>> So this is a more loose constraint than what we currently do,
>> that is, -EINVAL on (size > sizeof(attr)) where attr is the
>> currently known size of a specific kernel. That would at least
>> be a start, you won't be able to cover everything though, but
>> it would allow to address the issue raised when running with
>> a basic feature set.
>
> you missed my point. We should not 'do a start', since it
> doesn't help user space in the long run and only makes
> kernel more complex.

Sorry, I don't think I missed your point. But if you see things
differently, fair enough, it was just a suggestion.
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