linux-kernel - Re: [PATCH v6] x86/resctrl: Fix task CLOSID/RMID update race

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Message-ID: <CALPaoCiQmh-t_Wj8mzr6+_EUo_9x2=xVQOYh0_NSP+sVHGvCtA@mail.gmail.com>
Date:   Tue, 20 Dec 2022 17:07:17 +0100
From:   Peter Newman <peternewman@...gle.com>
To:     reinette.chatre@...el.com, fenghua.yu@...el.com
Cc:     bp@...en8.de, derkling@...gle.com, eranian@...gle.com,
        hpa@...or.com, james.morse@....com, jannh@...gle.com,
        kpsingh@...gle.com, linux-kernel@...r.kernel.org, mingo@...hat.com,
        tglx@...utronix.de, x86@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH v6] x86/resctrl: Fix task CLOSID/RMID update race

On Fri, Dec 16, 2022 at 2:31 PM Peter Newman <peternewman@...gle.com> wrote:
> In a memory bandwidth-metered compute host, malicious jobs could exploit
> this race to remain in a previous CLOSID or RMID in order to dodge a
> class-of-service downgrade imposed by an admin or to steal bandwidth.

After discussing with Reinette some more[1], I think the payoff of
exploiting this is too little for this to concern me, so I'll remove
the paragraph above.

[1] https://lore.kernel.org/lkml/CALPaoCi8hcFzNN9O9fS9Etri_KMdU32UU1tJsfeO1OxR-i1j7g@mail.gmail.com/

Consequently I don't think this fix is critical enough to be needed on
stable, so I'll drop the CC: stable from the update.