linux-kernel - Re: [PATCH] x86/msr: Block writes to certain MSRs unconditionally

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Date:   Sun, 11 Apr 2021 09:03:34 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Feng Tang <feng.tang@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Len Brown <len.brown@...el.com>
Subject: Re: [PATCH] x86/msr: Block writes to certain MSRs unconditionally

On Sat, Apr 10, 2021 at 11:52 AM Andi Kleen <ak@...ux.intel.com> wrote:
>
> Borislav Petkov <bp@...en8.de> writes:
>
> > From: Borislav Petkov <bp@...e.de>
> > Date: Sat, 10 Apr 2021 14:08:13 +0200
> >
> > There are a bunch of MSRs which luserspace has no business poking at,
> > whatsoever. Add a ban list and put the TSC-related MSRs in there. Issue
> > a big juicy splat to catch offenders.
>
> Have you ever seen any user programs actually write those MSRs?
> I don't see why they ever would, it's not that they have any motivation
> to do it (unlike SMM), and I don't know of any examples.

I have actually seen real user programs poke MSR_SYSCALL_MASK.