linux-kernel - Re: [PATCH] x86/vdso: Add prctl to set per-process VDSO load

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Message-ID: <CADU+-uBMc9THr0ADntsOqwh1--ULYMcssgPBvTesvFR+KQUfRg@mail.gmail.com>
Date:	Fri, 19 Sep 2014 15:02:54 -0700
From:	Filipe Brandenburger <filbranden@...gle.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Greg Thelen <gthelen@...gle.com>,
	X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Michael Davidson <md@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	Richard Larocque <rlarocque@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] x86/vdso: Add prctl to set per-process VDSO load

Hi Andy,

On Fri, Sep 19, 2014 at 12:27 PM, Andy Lutomirski <luto@...capital.net> wrote:
> I have this (special mapping tracking) 3/4 implemented.  I'm planning
> on making it fully functional for 64-bit programs and almost correct
> for 32-bit.  (You'll still crash if you have multiple threads, you use
> sysenter, and you remap the vdso, but I think that this is essentially
> unavoidable until someone lets mremap work on multiple vmas at once.)

In case that's useful, I was looking at swapping the vvar page by
changing the vm_special_mapping to change the pages array between the
actual vvar page and the zero page and using zap_page_range to force
the next access to go through a page fault that would remap it.

I didn't have all the details figured out (I was closer to 1/4 of it
implemented) but I didn't see any issues on 32-bit programs.

Let me know if you'd like to see some of my patches or if you think I
should keep working on them.

Cheers,
Filipe
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