linux-kernel - Re: [PATCH RFC 0/9] PKS write protected page tables

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Message-ID: <20210506000013.GE1068722@iweiny-DESK2.sc.intel.com>
Date:   Wed, 5 May 2021 17:00:13 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Rick Edgecombe <rick.p.edgecombe@...el.com>, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org, linux-mm@...ck.org,
        x86@...nel.org, akpm@...ux-foundation.org,
        linux-hardening@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, rppt@...nel.org,
        dan.j.williams@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/9] PKS write protected page tables

On Tue, May 04, 2021 at 11:25:31PM -0700, Kees Cook wrote:
> On Tue, May 04, 2021 at 05:30:23PM -0700, Rick Edgecombe wrote:
> 
> > Performance impacts
> > ===================
> > Setting direct map permissions on whatever random page gets allocated for a 
> > page table would result in a lot of kernel range shootdowns and direct map 
> > large page shattering. So the way the PKS page table memory is created is 
> > similar to this module page clustering series[2], where a cache of pages is 
> > replenished from 2MB pages such that the direct map permissions and associated 
> > breakage is localized on the direct map. In the PKS page tables case, a PKS 
> > key is pre-applied to the direct map for pages in the cache.
> > 
> > There would be some costs of memory overhead in order to protect the direct 
> > map page tables. There would also be some extra kernel range shootdowns to 
> > replenish the cache on occasion, from setting the PKS key on the direct map of 
> > the new pages. I don’t have any actual performance data yet.
> 
> What CPU models are expected to have PKS?


Supervisor Memory Protection Keys (PKS) is a feature which is found on Intel’s
Sapphire Rapids (and later) “Scalable Processor” Server CPUs.  It will also be
available in future non-server Intel parts.

Also qemu has some support as well.

https://www.qemu.org/2021/04/30/qemu-6-0-0/

Ira