netdev - Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 17 Feb 2012 05:51:25 +0100
From:	"Indan Zupancic" <indan@....nu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Andrew Lutomirski" <luto@....edu>,
	"Will Drewry" <wad@...omium.org>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
	kernel-hardening@...ts.openwall.com, netdev@...r.kernel.org,
	x86@...nel.org, arnd@...db.de, davem@...emloft.net,
	mingo@...hat.com, oleg@...hat.com, peterz@...radead.org,
	rdunlap@...otime.net, mcgrathr@...omium.org, tglx@...utronix.de,
	eparis@...hat.com, serge.hallyn@...onical.com, djm@...drot.org,
	scarybeasts@...il.com, pmoore@...hat.com,
	akpm@...ux-foundation.org, corbet@....net, eric.dumazet@...il.com,
	markus@...omium.org, keescook@...omium.org
Subject: Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF

On Fri, February 17, 2012 05:09, H. Peter Anvin wrote:
> On 02/16/2012 07:27 PM, Indan Zupancic wrote:
>>
>> A JIT won't be able to merge accesses because it also has to merge other
>> instructions and recognize when 64-bit operations are done with 32-bit
>> instructions. I think that will be too hard for a JIT.
>>
>
> Please Google "peephole optimizer".

I have written one for uni. Like I said, I think it will be too hard
for a BPF JIT because the pattern is too complex. Keep in mind that
there is no 64-bit register where you can load the data to, everything
is done on 32-bit values. So you have to recognize 32-bit code emulating
64-bit ops. I don't think anyone will add all the different patterns of
doing that to the JIT, there are too many.

The current JIT is networking-only and is very simplistic. It is a very
long way to a sophisticated enough JIT that does such complex peephole
optimisations. I'm not saying it's impossible in general, just that the
kernel BPF JIT won't be able to do it. It's a lot easier to just add
64-bit support to BPF instead.

Greetings,

Indan

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html