linux-kernel - Re: [RFC PATCH] x86/msr: Filter MSR writes

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Message-ID: <20200612170303.GD22660@zn.tnic>
Date:   Fri, 12 Jun 2020 19:03:03 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     x86-ml <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86/msr: Filter MSR writes

On Fri, Jun 12, 2020 at 09:57:09AM -0700, Sean Christopherson wrote:
> DS_AREA takes a virtual (linear) address, i.e. the address can be legal from
> the CPUs perspective but still lead to a #PF due to the address not being
> mapped in the page tables.

It's not that - peterz and tglx - and I assume you meant that too - you
all want to taint on the very *attempt* to WRMSR, regardless of whether
the MSR exists or not.

I don't necessarily agree with that because I don't think we should
taint when the MSR doesn't exist but if you all want it, sure, whatever.
I don't care that deeply.

> So users don't have to unload and reload the module just to enable or
> disable writes.  I don't think it changes the protections in any way, a
> priveleged user still needs to explicitly toggle the control.

There's /sys/module/msr/parameters/. A privileged user can do whatever.
A non-privileged should not disable that.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette