linux-kernel - Re: [PATCH 30/30] x32: Add x32 VDSO support

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Message-ID: <4F43F25E.3030004@zytor.com>
Date:	Tue, 21 Feb 2012 11:37:02 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Lutomirski <luto@....edu>
CC:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	mingo@...nel.org, tglx@...utronix.de,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	hjl.tools@...il.com
Subject: Re: [PATCH 30/30] x32: Add x32 VDSO support

On 02/21/2012 11:29 AM, Andrew Lutomirski wrote:
>>
>> The vsyscall page shouldn't be mapped for x32 tasks...
> 
> How is that possible?  It lives in the fixmap and is presumably
> visible from any 64-bit code.
> 
> Admittedly, x32 tasks are probably somewhat difficult to trick into
> calling addresses with high bits set, but it's not necessarily
> impossible.
> 

Fair enough, and it's not necessarily all that hard either.

And it's visible even in a 32-bit task, although a 32-bit task has to
switch into 64-bit mode.  Yet another reason the vsyscall page needs to die.

I was having delusions that we could have a task-owned PDT in negative
space, but that would require unsharing the third level, too, which is
just way too messy.

	-hpa
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