linux-kernel - RE: [PATCH v5 2/3] x86/bus_lock: Handle #DB for bus lock

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Message-ID: <d98d86f9f5824573b2441089e0c2ae91@intel.com>
Date:   Fri, 19 Mar 2021 21:50:02 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
CC:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        "Yu, Fenghua" <fenghua.yu@...el.com>
Subject: RE: [PATCH v5 2/3] x86/bus_lock: Handle #DB for bus lock

>  What is the justifucation for making this rate limit per UID and not
>  per task, per process or systemwide?

The concern is that a malicious user is running a workload that loops
obtaining the buslock. This brings the whole system to its knees.

Limiting per task doesn't help. The user can just fork(2) a whole bunch
of tasks for a distributed buslock attack..

Systemwide might be an interesting alternative. Downside would be accidental
rate limit of non-malicious tasks that happen to grab a bus lock periodically
but in the same window with other buslocks from other users.

Do you think that a risk worth taking to make the code simpler?

-Tony