linux-kernel - Re: [PATCH] x86/msr: do not warn on writes to OC

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Date:   Tue, 8 Sep 2020 20:01:12 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        kitsunyan <kitsunyan@...mail.cc>,
        "Brown, Len" <len.brown@...el.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sultan Alsawaf <sultan@...neltoast.com>
Subject: Re: [PATCH] x86/msr: do not warn on writes to OC_MAILBOX

On Tue, Sep 08, 2020 at 07:42:12PM +0200, Jason A. Donenfeld wrote:
> Are you prepared to track down all the MSRs that might maybe do
> something naughty?

I'm not prepared - that's why this MSR filtering. To block *all* direct
MSR accesses from userspace in the future.

> Does `dd` warn when you run `dd if=/dev/zero of=/dev/sda`?

Yah, because that's the same as bricking your hardware. Geez.

> Probably not possible. Optimal values are related to the "silicon
> lottery" that occurs when you buy a new CPU. Different optimal values
> for different individual chips.

Let's wait for what Srinivas finds out. I'd let Intel decide what they
wanna do.

-- 
Regards/Gruss,
    Boris.

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