linux-kernel - Re: [PATCH v2 2/3] arm64: Add seccomp support

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Message-ID: <20140306152458.GG5202@mudshark.cambridge.arm.com>
Date:	Thu, 6 Mar 2014 15:24:58 +0000
From:	Will Deacon <will.deacon@....com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	"wad@...omium.org" <wad@...omium.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"arndb@...db.de" <arndb@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] arm64: Add seccomp support

On Thu, Mar 06, 2014 at 02:34:46AM +0000, AKASHI Takahiro wrote:
> On 03/01/2014 02:20 AM, Will Deacon wrote:
> > On Tue, Feb 25, 2014 at 09:20:24AM +0000, AKASHI Takahiro wrote:
> > I'm slightly surprised that we do the secure computing check first. Doesn't
> > this allow a debugger to change the syscall to something else after we've
> > decided that it's ok?
> 
> To be honest, I just followed other architectures' implementation.
> Can you elaborate any use case that you have in your mind?

My initial thought was that we should do the secure_computing check *after*
the debugger has finished messing around with the registers. However, I
suppose you'd have had to enable ptrace in your seccompd filter for that
scenario to occur, so there's probably not an issue here after all.

Will
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