linux-kernel - Re: [PATCH 0/3] arm64:msr: Add MSR driver

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Message-ID: <20201130190331.GI6019@zn.tnic>
Date:   Mon, 30 Nov 2020 20:03:31 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Rongwei Wang <rongwei.wang@...ux.alibaba.com>
Cc:     catalin.marinas@....com, will@...nel.org,
        bjorn.andersson@...aro.org, shawnguo@...nel.org, vkoul@...nel.org,
        geert+renesas@...der.be, Anson.Huang@....com, michael@...le.cc,
        krzk@...nel.org, olof@...om.net, vincenzo.frascino@....com,
        ardb@...nel.org, masahiroy@...nel.org, gshan@...hat.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] arm64:msr: Add MSR driver

On Tue, Dec 01, 2020 at 01:48:30AM +0800, Rongwei Wang wrote:
> MSR ARM driver aims to provide interfacs for user to read or write
> data to all system registers.

Just a warranty from x86 land: if I were an ARM arch maintainer, I would
never never *ever* take such driver exposing naked hw registers to
userspace.

We have been fighting with this on x86 for years:

a7e1f67ed29f ("x86/msr: Filter MSR writes")

with userspace tools poking at random MSRs. Read the commit message
for what can happen. And taking that thing is like opening a huge
can'o'worms that can't be closed anymore.

Currently, we're trying to move userspace tools to proper sysfs
interfaces but it is a huuuge pain. It is a lot easier to have people
define proper interfaces from the get-go where the kernel can control
and synchronize access.

HTH.

-- 
Regards/Gruss,
    Boris.

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