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From:   Richard Hughes <hughsient@gmail.com>
Date:   Fri, 19 Jun 2020 15:09:09 +0100
Message-ID: <CAD2FfiHCi2MfShGWaYWk_GcXW4xVr6chsLPZs78OJE+2_GErVg@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 14:58, Dave Hansen <dave.hansen@intel.com> wrote:
> > Right, but for the most part you'd agree that a machine with
> > functioning TME and encrypted swap partition is more secure than a
> > machine without TME?
>
> Nope.  There might be zero memory connected to the memory controller
> that supports TME.

So you're saying that a machine with TME available and enabled is not
considered more secure than a machine without TME?

What I want to do is have a sliding scale of TME not available < TME
available but disabled < TME available and enabled < TME available,
enabled and being used. The extra nugget of data gets me from state 2
to state 3.

> > Can I use TME if the CPU supports it, but the platform has disabled
> > it? How do I know that my system is actually *using* the benefits the
> > TME feature provides?
>
> You must have a system with UEFI 2.8, ensure TME is enabled, then make
> sure the OS parses EFI_MEMORY_CPU_CRYPTO, then ensure you request that
> you data be placed in a region marked with EFI_MEMORY_CPU_CRYPTO, and
> that it be *kept* there (hint: NUMA APIs don't do this).

So my take-away from that is that it's currently impossible to
actually say if your system is *actually* using TME.

Richard.