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From:   Richard Hughes <hughsient@gmail.com>
Date:   Fri, 19 Jun 2020 15:36:28 +0100
Message-ID: <CAD2FfiF8QEarhyFD1GkfnaR+spyH86sChgRZm37ab_gzS2m_wg@mail.gmail.com>
Subject: Re: [PATCH] Ability to read the MKTME status from userspace
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Daniel Gutson <daniel@eclypsium.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>, Tony Luck <tony.luck@intel.com>,
        Rahul Tanwar <rahul.tanwar@linux.intel.com>,
        Xiaoyao Li <xiaoyao.li@intel.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Fri, 19 Jun 2020 at 15:23, Dave Hansen <dave.hansen@intel.com> wrote:
> Last night, I asked my kids if they brushed their teeth.  They said:
> "Dad, my toothbrush was available."  They argued that mere availability
> was a better situation than not *having* a toothbrush.  They were
> logically right, of course, but they still got cavities.

I don't see how that's comparable, sorry. Surely Intel wants to sell
hardware advertising TME as a security feature?

> > So my take-away from that is that it's currently impossible to
> > actually say if your system is *actually* using TME.
> Not in a generic way, and it can't be derived from cpuid or MSRs alone.

Well, it seems not in any way at the moment.

> I'm pretty sure I'm using TME, but I didn't become sure from
> poking at sysfs.

How do you know that Lenovo didn't disable TME without looking at
dmesg? I don't think "pretty sure" is good enough when TME is
considered a security feature.

Richard