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

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Message-ID: <CALCETrU0=_9voz1bxbLom=y7qnk7RN7U5Bd2s+Dk_QQN2yYVfw@mail.gmail.com>
Date:	Tue, 16 Sep 2014 22:34:18 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Richard Larocque <rlarocque@...gle.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Filipe Brandenburger <filbranden@...gle.com>,
	Michael Davidson <md@...gle.com>,
	Greg Thelen <gthelen@...gle.com>, X86 ML <x86@...nel.org>,
	Linux API <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/vdso: Add prctl to set per-process VDSO load

On Tue, Sep 16, 2014 at 10:00 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, Sep 16, 2014 at 6:18 PM, Richard Larocque <rlarocque@...gle.com> wrote:
>> On Tue, Sep 16, 2014 at 5:27 PM, Andy Lutomirski <luto@...capital.net> wrote:
> I think that the patch should instead tweak the vvar mapping to tell
> the vdso not to use rdtsc.  It should be based on this:
>
> https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=x86/vsyscall
>
> and I'll talk to hpa tomorrow about about getting that, or something
> like it, into the tip tree.  In particular, you'll need this:
>
> https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=x86/vsyscall&id=0cc410a05cb95e073ebfe099c9e03cef48d2be0f

Crud.  Now that I've said that, I realize that this won't work right
if rdtscp is off.  I'll drop that patch.

I don't think that this changes the conclusion.  It should be possible
to swap out the vvar page to keep the vdso working even without rdtsc
available.

--Andy

>
> Also, this kind of inheritable restriction may end up requiring
> no_new_privs or CAP_SYS_ADMIN to be secure.
>
> --Andy



-- 
Andy Lutomirski
AMA Capital Management, LLC
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