linux-kernel - Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas

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Date:   Wed, 26 Aug 2020 21:01:17 +0200
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alan Cox <alan@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christopher Lameter <cl@...ux.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Reshetova\, Elena" <elena.reshetova@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>,
        Linux API <linux-api@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas

* Andy Lutomirski:

>> I _believe_ there are also things like AES-NI that can get strong
>> protection from stuff like this.  They load encryption keys into (AVX)
>> registers and then can do encrypt/decrypt operations without the keys
>> leaving the registers.  If the key was loaded from a secret memory area
>> right into the registers, I think the protection from cache attacks
>> would be pretty strong.
>
> Except for context switches :)

An rseq sequence could request that the AVX registers should be
cleared on context switch.  (I'm mostly kidding.)

I think the main issue is that we do not have a good established
programming model to actually use such features and completely avoid
making copies of secret data.