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

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Message-ID: <CAObL_7H=M7-wxobKkj+K2fcrpEv0Nfp8=6gV2yvdb2hqxCTAGg@mail.gmail.com>
Date:	Tue, 21 Feb 2012 11:40:38 -0800
From:	Andrew Lutomirski <luto@....edu>
To:	"H. Peter Anvin" <hpa@...or.com>
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 Tue, Feb 21, 2012 at 11:37 AM, H. Peter Anvin <hpa@...or.com> wrote:
> 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.

I'd like to do that, too, and I'd also like to have a per-cpu
kernel-only page in there, but that's even worse.  If we had a
separate cr3-like register for negative addresses, life would be good
:)

--Andy
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