From: Paolo Bonzini <pbonzini@redhat.com>
To: speck@linutronix.de
Subject: [MODERATED] Re: LVI
Date: Tue, 26 Nov 2019 11:55:21 +0100 [thread overview]
Message-ID: <e43ebda7-90fc-f44d-84e9-a0edcd4d10fd@redhat.com> (raw)
In-Reply-To: <20191126005417.GG84886@tassilo.jf.intel.com>
[-- Attachment #1: Type: text/plain, Size: 1308 bytes --]
On 26/11/19 01:54, speck for Andi Kleen wrote:
>
> Hi Folks,
>
> We (well Tony, but he's currently on vacation) did a lot of analysis on LVI and we
> concluded the kernel does not need any new changes. That's why you didn't see any
> patches from Intel on this.
>
> Longer story:
>
> Assists are somewhat messy and can happen in many circumstances. However most
> are rare and hard to trigger, so if you get them they're typically not usable
> for a high loop count practical side channel. The main exception is the page A/D
> assist which can be triggered in the kernel by *_user()
>
> *_user is protected by STAC/CLAC already and those have strong enough semantics
> to stop an LVI attack outside the uaccess region. But of course there are CPUs
> (pre BDW) which don't have STAC/CLAC.
>
> But to do anything with LVI you need a Spectre v1 style read gadget. Without
> a gadget the attack is not feasible. And those gadgets are usually Spectre v1
> problems, so they would need to be fixed anyways.
Don't you need only half of a Spectrev1 gadget (see the Xen advisory at
https://xenbits.xen.org/xsa/advisory-289.html and the KVM patch at
https://marc.info/?l=kvm&m=157444806904659&w=2)? Also I assume you
didn't take into account using vmexits as an assist.
Paolo
next prev parent reply other threads:[~2019-11-26 10:55 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 17:40 [MODERATED] LVI Josh Poimboeuf
2019-11-19 17:51 ` [MODERATED] LVI Andrew Cooper
2019-11-19 18:27 ` Josh Poimboeuf
2019-11-19 19:26 ` Andrew Cooper
2019-11-20 9:52 ` Paolo Bonzini
2019-11-19 18:12 ` Greg KH
2019-11-19 18:21 ` Josh Poimboeuf
2019-11-19 18:46 ` Greg KH
2019-11-19 18:21 ` Paolo Bonzini
2019-11-19 18:22 ` Andrew Cooper
2019-11-19 18:27 ` Josh Poimboeuf
2019-11-19 18:36 ` Luck, Tony
2019-11-20 17:02 ` Greg KH
2019-11-19 18:39 ` Andrew Cooper
2019-11-19 21:00 ` Josh Poimboeuf
2019-11-19 21:03 ` Josh Poimboeuf
2019-11-20 14:11 ` Andrew Cooper
2019-11-20 8:04 ` Peter Zijlstra
2019-11-20 9:49 ` Andrew Cooper
2019-11-20 17:13 ` Josh Poimboeuf
2019-11-20 17:25 ` Greg KH
2019-11-20 17:29 ` Tyler Hicks
2019-11-20 17:30 ` Andrew Cooper
2019-11-20 17:46 ` Greg KH
2019-11-20 19:09 ` Peter Zijlstra
2019-11-20 19:19 ` Greg KH
2019-11-21 0:50 ` LVI Thomas Gleixner
2019-11-21 13:45 ` [MODERATED] LVI Greg KH
2019-11-26 0:54 ` Andi Kleen
2019-11-26 10:37 ` Greg KH
2019-11-26 18:23 ` Andi Kleen
2019-11-27 7:38 ` Greg KH
2019-11-26 10:55 ` Paolo Bonzini [this message]
2019-11-26 18:28 ` Andi Kleen
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