linux-kernel - Re: [RFC PATCH v4 00/19] Core scheduling v4

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Date:   Tue, 17 Mar 2020 14:58:28 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Joel Fernandes <joel@...lfernandes.org>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Dario Faggioli <dfaggioli@...e.com>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Luck, Tony" <tony.luck@...el.com>
Subject: Re: [RFC PATCH v4 00/19] Core scheduling v4



On 3/17/20 2:17 PM, Thomas Gleixner wrote:

>> The interrupt handler will be run with PTE inverted.  So I don't think
>> there's a leak via L1TF in this scenario.
> 
> How so?
> 
> Host memory is attackable, when one of the sibling SMT threads runs in
> host OS (hypervisor) context and the other in guest context.
> 
> HT1 is in guest mode and attacking (has control over PTEs). HT2 is
> running in host mode and executes an interrupt handler. The host PTE
> inversion does not matter in this scenario at all.
> 
> So HT1 can very well see data which is brought into the shared L1 by
> HT2.
> 
> The only way to mitigate that aside of disabling HT is disabling EPT.
> 

I had a brain lapse. Yes, PTE inversion is for mitigating against malicious
user space code, not for malicious guest.

Thanks for the correction.

Tim