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

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Message-ID: <CAObL_7GLnDFkb61jAZEj+9gGTr4FA=8ZFVMxd9Tus4LVVmKjKw@mail.gmail.com>
Date:	Tue, 21 Feb 2012 11:29:00 -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 11:03 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 02/21/2012 10:54 AM, Andrew Lutomirski wrote:
>>
>> uclibc hardcodes a call to the vsyscall gettimeofday implementation in
>> its locking primitives, which probably gives terrible performance, but
>> that's a separate issue.  I think do_emulate_vsyscall should send a
>> segfault if called by an x32 task -- there's some security benefit to
>> doing so, and there's unlikely to be any downside.
>>
>
> 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.

--Andy
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