Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200907094843.1949-1-Jason@zx2c4.com> <20200907100647.GB10657@zn.tnic>
 <22617e57e541e460fac09db04fdb370f8e96e8ef.camel@linux.intel.com>
 <CAHmME9rh8N-Qui2KVxGP33Aar5tao_obA70XKwR2x5Qp1AytTw@mail.gmail.com>
 <20200908172558.GG25236@zn.tnic> <CAHmME9pKfvPGf97BM1=VdUL1uU_8aOoc4+QOu6b51XnPz3SkRA@mail.gmail.com>
 <20200908173656.GI25236@zn.tnic> <CAHmME9pVO01mj8vgKPEX7a6pZDRSfX62e2Ow8R=L79hLSJoaMA@mail.gmail.com>
 <20200908180112.GK25236@zn.tnic>
In-Reply-To: <20200908180112.GK25236@zn.tnic>
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Tue, 8 Sep 2020 21:07:20 +0200
Message-ID: <CAHmME9rMbuXfR+eNhopX8FyeXerUrPo4vaWpF6Dx-u3NnTmrVg@mail.gmail.com>
Subject: Re: [PATCH] x86/msr: do not warn on writes to OC_MAILBOX
To:     Borislav Petkov <bp@alien8.de>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        kitsunyan <kitsunyan@airmail.cc>,
        "Brown, Len" <len.brown@intel.com>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sultan Alsawaf <sultan@kerneltoast.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Sep 8, 2020 at 8:01 PM Borislav Petkov <bp@alien8.de> wrote:
>
> 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.

Nobody is talking about bricking any hardware. Sorry if I seemed to
imply that before. In my experience, undervolting improperly results
in the CPU calculating things wrong and eventually crashing, and
overclocking usually will trip some thermal limits where the CPU
powers down. I've never experienced bricked hardware as a result of
this.

Jason