linux-kernel - Re: Pondering per-process vsyscall disablement

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Date:	Wed, 28 May 2014 14:45:18 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>, Marian Marinov <mm@...com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Linux API <linux-api@...r.kernel.org>
Subject: Re: Pondering per-process vsyscall disablement

On 05/23/2014 09:40 AM, Andy Lutomirski wrote:
> 
> I don't think this should be something configured by the
> administrator, unless the administrator is the builder of a kiosky
> thing like Chromium OS.  In that case, the administrator can use
> vsyscall=none.
> 
> I think this should be handled by either libc or the toolchain, hence
> the suggestions of a syscall or an ELF header.
> 

We could mimic the NX stack stuff, but it would have a lot of false
negatives, simply because very few things would actually poke at the
vsyscall page.

The NX stuff uses a dummy program header in the ELF image.

On the other hand, you could make the argument that anything compiled
with a new toolchain simply should not use the vsyscall page, and just
unconditionally set the opt-out bit (header) in question.

It might be better to have some kind of flags field (which a number of
architectures use) than keep using dummy program headers, though.

	-hpa

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