linux-kernel - Re: [RFC PATCH v3 1/2] x86: cpu/bugs: add AMD ERAPS support; hardware flushes RSB

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: <7222b969-30a8-42de-b2ca-601f6d1b03cd@intel.com>
Date: Mon, 2 Dec 2024 09:26:16 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Amit Shah <amit@...nel.org>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, x86@...nel.org, linux-doc@...r.kernel.org
Cc: amit.shah@....com, thomas.lendacky@....com, bp@...en8.de,
 tglx@...utronix.de, peterz@...radead.org, jpoimboe@...nel.org,
 pawan.kumar.gupta@...ux.intel.com, corbet@....net, mingo@...hat.com,
 dave.hansen@...ux.intel.com, hpa@...or.com, seanjc@...gle.com,
 pbonzini@...hat.com, daniel.sneddon@...ux.intel.com, kai.huang@...el.com,
 sandipan.das@....com, boris.ostrovsky@...cle.com, Babu.Moger@....com,
 david.kaplan@....com, dwmw@...zon.co.uk, andrew.cooper3@...rix.com
Subject: Re: [RFC PATCH v3 1/2] x86: cpu/bugs: add AMD ERAPS support; hardware
 flushes RSB

On 11/28/24 05:28, Amit Shah wrote:
> From: Amit Shah <amit.shah@....com>
> 
> When Automatic IBRS is disabled, Linux flushed the RSB on every context
> switch.  This RSB flush is not necessary in software with the ERAPS
> feature on Zen5+ CPUs that flushes the RSB in hardware on a context
> switch (triggered by mov-to-CR3).
> 
> Additionally, the ERAPS feature also tags host and guest addresses in
> the RSB - eliminating the need for software flushing of the RSB on
> VMEXIT.
> 
> Disable all RSB flushing by Linux when the CPU has ERAPS.
> 
> Feature mentioned in AMD PPR 57238.  Will be resubmitted once APM is
> public - which I'm told is imminent.

There was a _lot_ of discussion about this. But all of that discussion
seems to have been trimmed out and it seems like we're basically back
to: "this is new hardware supposed to mitigate SpectreRSB, thus it
mitigates SpectreRSB."

Could we please summarize the previous discussions in the changelog?
Otherwise, I fear it will be lost.