linux-kernel - Re: [PATCH] net: filter: make JITs zero A for SKF_AD_ALU_XOR

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Message-ID: <20160105174309.GA83548@ast-mbp.thefacebook.com>
Date:	Tue, 5 Jan 2016 09:43:10 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	Rabin Vincent <rabin@....in>, davem@...emloft.net,
	netdev@...r.kernel.org, ast@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
	linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: filter: make JITs zero A for SKF_AD_ALU_XOR_X

On Tue, Jan 05, 2016 at 05:36:47PM +0100, Daniel Borkmann wrote:
> On 01/05/2016 04:23 PM, Rabin Vincent wrote:
> >The SKF_AD_ALU_XOR_X ancillary is not like the other ancillary data
> >instructions since it XORs A with X while all the others replace A with
> >some loaded value.  All the BPF JITs fail to clear A if this is used as
> >the first instruction in a filter.  This was found using american fuzzy
> >lop.
> >
> >Add a helper to determine if A needs to be cleared given the first
> >instruction in a filter, and use this in the JITs.  Except for ARM, the
> >rest have only been compile-tested.
> >
> >Fixes: 3480593131e0 ("net: filter: get rid of BPF_S_* enum")
> >Signed-off-by: Rabin Vincent <rabin@....in>
> 
> Excellent catch, thanks a lot! The fix looks good to me and should
> go to -net tree.
> 
> Acked-by: Daniel Borkmann <daniel@...earbox.net>

good catch indeed.
Classic bpf jits didn't have much love. Great to see this work.

Acked-by: Alexei Starovoitov <ast@...nel.org>

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