linux-kernel - Re: [RFC PATCH net-next 2/6] x86: bpf_jit_comp: support BPF_S_ANC_SECCOMP_LD

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Message-ID: <CAKU6vybrYK9oimKSEGhoLeNzhtk=7r3zouRgzDFqGwJHd=psGQ@mail.gmail.com>
Date:	Fri, 26 Apr 2013 11:29:27 -0400
From:	Xi Wang <xi.wang@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Daniel Borkmann <dborkman@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Russell King <linux@....linux.org.uk>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Will Drewry <wad@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net-next 2/6] x86: bpf_jit_comp: support
 BPF_S_ANC_SECCOMP_LD_W instruction

On Fri, Apr 26, 2013 at 11:11 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 2) Calling a function potentially destroys some registers.
>    %rdi,%r8,%r9 for instance, so we are going to crash very easily.
>
> I dont know, I feel a bit uncomfortable having to explain this to
> someone sending security related patches...

My old code did save these registers.  But, do we really need that for
seccomp?  For example, %rdi (skb) is always NULL and never used by
seccomp filters.  Did I miss anything?

- xi
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