netdev - Re: [PATCH RFC v4 net-next 01/26] net: filter: add "load 64-bit immediate" eBPF instruction

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Message-ID: <CAMEtUuwO028MV8TQXQew1SOQjUvSbQ_bazAqorGRxojXXYXEnA@mail.gmail.com>
Date:	Wed, 13 Aug 2014 14:38:23 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v4 net-next 01/26] net: filter: add "load 64-bit
 immediate" eBPF instruction

On Wed, Aug 13, 2014 at 2:27 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 08/13/2014 02:23 PM, Andy Lutomirski wrote:
>> On Wed, Aug 13, 2014 at 2:21 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>> One thing about this that may be a serious concern: allowing the user to
>>> control 8 contiguous bytes of kernel memory may be a security hazard.
>>
>> I'm confused.  What kind of memory?  I can control a lot more than 8
>> bytes of stack very easily.
>>
>> Or are you concerned about 8 contiguous bytes of *executable* memory?
>>
>
> Yes.  Useful for some kinds of ROP custom gadgets.

I don't get it. What is ROP ?
What is the concern about 8 bytes ?
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