linux-kernel - Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6cc985bb-6aed-4fb7-0ef2-43aad2717095@oracle.com>
Date:   Wed, 24 Oct 2018 16:30:42 +0530
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     "Stecklina, Julian" <jsteckli@...zon.de>
Cc:     "juerg.haefliger@....com" <juerg.haefliger@....com>,
        "deepa.srinivasan@...cle.com" <deepa.srinivasan@...cle.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
        "pradeep.vincent@...cle.com" <pradeep.vincent@...cle.com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "kanth.ghatraju@...cle.com" <kanth.ghatraju@...cle.com>,
        "joao.m.martins@...cle.com" <joao.m.martins@...cle.com>,
        "liran.alon@...cle.com" <liran.alon@...cle.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "keescook@...gle.com" <keescook@...gle.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "chris.hyser@...cle.com" <chris.hyser@...cle.com>,
        "tyhicks@...onical.com" <tyhicks@...onical.com>,
        "john.haxby@...cle.com" <john.haxby@...cle.com>,
        "jcm@...hat.com" <jcm@...hat.com>
Subject: Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs
 in mind (for KVM to isolate its guests per CPU)

On 10/15/2018 01:37 PM, Khalid Aziz wrote:
> On 09/24/2018 08:45 AM, Stecklina, Julian wrote:
>> I didn't test the version with TLB flushes, because it's clear that the
>> overhead is so bad that no one wants to use this.
> 
> I don't think we can ignore the vulnerability caused by not flushing 
> stale TLB entries. On a mostly idle system, TLB entries hang around long 
> enough to make it fairly easy to exploit this. I was able to use the 
> additional test in lkdtm module added by this patch series to 
> successfully read pages unmapped from physmap by just waiting for system 
> to become idle. A rogue program can simply monitor system load and mount 
> its attack using ret2dir exploit when system is mostly idle. This brings 
> us back to the prohibitive cost of TLB flushes. If we are unmapping a 
> page from physmap every time the page is allocated to userspace, we are 
> forced to incur the cost of TLB flushes in some way. Work Tycho was 
> doing to implement Dave's suggestion can help here. Once Tycho has 
> something working, I can measure overhead on my test machine. Tycho, I 
> can help with your implementation if you need.

I looked at Tycho's last patch with batch update from 
<https://lkml.org/lkml/2017/11/9/951>. I ported it on top of Julian's 
patches and got it working well enough to gather performance numbers. 
Here is what I see for system times on a machine with dual Xeon E5-2630 
and 256GB of memory when running "make -j30 all" on 4.18.6 kernel 
(percentages are relative to base 4.19-rc8 kernel without xpfo):


Base 4.19-rc8				913.84s
4.19-rc8 + xpfo, no TLB flush		1027.985s (+12.5%)
4.19-rc8 + batch update, no TLB flush	970.39s (+6.2%)
4.19-rc8 + xpfo, TLB flush		8458.449s (+825.6%)
4.19-rc8 + batch update, TLB flush	4665.659s (+410.6%)

Batch update is significant improvement but we are starting so far 
behind baseline, it is still a huge slow down.

--
Khalid