linux-kernel - Re: [PATCH RFC 0/2] Selective mitigation for trusted userspace

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Message-ID: <ydu5mlvvvizkadyspu52afbdoyjq7akyx2665l3zit2tj6cs3s@4edufjodwmbu>
Date: Fri, 27 Sep 2024 17:52:35 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, David Kaplan <David.Kaplan@....com>, 
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH RFC 0/2] Selective mitigation for trusted userspace

Hello.

On Thu, Sep 19, 2024 at 02:52:31PM GMT, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> wrote:
> This is an experimental series exploring the feasibility of selectively
> applying CPU vulnerability mitigations on a per-process basis. The
> motivation behind this work is to address the performance degradation
> experienced by trusted user-space applications due to system-wide CPU
> mitigations.

This is an interesting idea (like an extension of core scheduling).

> The rationale for choosing the cgroup interface over other potential
> interfaces, such as LSMs, is cgroup's inherent support for core scheduling.

You don't list prctl (and process inheritance) interface here.

> Core scheduling allows the grouping of tasks such that they are scheduled
> to run on the same cores. 

And that is actually the way how core scheduling is implemented AFAICS
-- cookie creation and passing via prctls.
Thus I don't find the implementation via a cgroup attribute ideal.

(I'd also say that cgroups are more organization/resource domains but
not so much security domains.)


> - Should child processes inherit the parent's unmitigated status?

Assuming turning off mitigations is a a privileged operation, the
fork could preserve it. It would be upon parent to clear it up properly
before handing over execution to a child (cf e.g. dropping uid=0).

HTH,
Michal

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