netdev - RE: [PATCH] arm64: net: bpf: don't BUG() on large shifts

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Date:	Thu, 7 Jan 2016 11:07:39 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Alexei Starovoitov' <alexei.starovoitov@...il.com>,
	Rabin Vincent <rabin@....in>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"zlim.lnx@...il.com" <zlim.lnx@...il.com>,
	"yang.shi@...aro.org" <yang.shi@...aro.org>,
	"will.deacon@....com" <will.deacon@....com>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] arm64: net: bpf: don't BUG() on large shifts

From: Alexei Starovoitov
> Sent: 06 January 2016 22:13
> On Wed, Jan 06, 2016 at 09:31:27PM +0100, Rabin Vincent wrote:
> > On Tue, Jan 05, 2016 at 09:55:58AM -0800, Alexei Starovoitov wrote:
> > > this one is better to be addressed in verifier instead of eBPF JITs.
> > > Please reject it in check_alu_op() instead.
> >
> > AFAICS the eBPF verifier is not called on the eBPF filters generated by
> > the BPF->eBPF conversion in net/core/filter.c, so performing this check
> > only in check_alu_op() will be insufficient.  So I think we'd need to
> > add this check to bpf_check_classic() too.  Or am I missing something?
> 
> correct. the check is needed in bpf_check_classic() too and I believe
> it's ok to tighten it up in this case, since >32 shift is
> invalid/undefined anyway. We can either accept it as nop or K&=31
> or error. I think returning error is more user friendly long term, though
> there is a small risk of rejecting previously loadable broken programs.

Or replace with an assignment of zero?

	David

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