linux-kernel - Re: [PATCHv6 01/16] x86/cpu: Enumerate the LASS feature bits

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Message-ID: <ztkgdk72p2z3q6z4hslfg4gj6pejirh7cnssxhd7u72mo4enn4@viqrwrycderf>
Date: Mon, 23 Jun 2025 16:42:41 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Andy Lutomirski <luto@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
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	linux-mm@...ck.org, Yian Chen <yian.chen@...el.com>
Subject: Re: [PATCHv6 01/16] x86/cpu: Enumerate the LASS feature bits

On Mon, Jun 23, 2025 at 12:21:05PM +0200, Borislav Petkov wrote:
> On Mon, Jun 23, 2025 at 11:17:02AM +0300, Kirill A. Shutemov wrote:
> > What about this:
> > 
> > LASS provides protection against a class of speculative attacks, such as
> > SLAM[1]. Add the "lass" flag to /proc/cpuinfo to indicate that the feature
> > is supported by hardware and enabled by the kernel. This allows userspace
> > to determine if the setup is secure against such attacks.
> 
> Yeah, thanks.
> 
> I'm still not fully on board with userspace determining whether they're
> mitigated or not but that's a general problem with our mitigations.
> 
> Also, I haven't looked at the patchset yet but I think it should be also
> adding code to bugs.c to make all those vulns which it addresses, report that
> they're mitigated by LASS now in
> 
> grep -r . /sys/devices/system/cpu/vulnerabilities/
> 
> output.
> 
> Which makes your cpuinfo flag not really needed as we already have a special
> method for the mitigations reporting.
> 
> But ok, it has gotten kernel enablement so stating so in cpuinfo is ok.

Due to SLAM, we decided to postpone LAM enabling, until LASS is landed.

I am not sure if we want to add static
/sys/devices/system/cpu/vulnerabilities/slam with "Mitigation: LASS".

There might be other yet-to-be-discovered speculative attacks that LASS
mitigates. Security features have to visible to userspace independently of
known vulnerabilities.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov