linux-kernel - Re: [PATCH] Ability to read the MKTME status from userspace

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Message-ID: <d55f94bc-3b26-a556-f7e6-43e9b1007e13@intel.com>
Date:   Fri, 19 Jun 2020 06:58:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Richard Hughes <hughsient@...il.com>
Cc:     Daniel Gutson <daniel@...ypsium.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Rahul Tanwar <rahul.tanwar@...ux.intel.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Ability to read the MKTME status from userspace

On 6/19/20 6:37 AM, Richard Hughes wrote:
> On Fri, 19 Jun 2020 at 14:33, Dave Hansen <dave.hansen@...el.com> wrote:
>> On top of that, the kernel can just swap data out to unencrypted storage.
> 
> 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, I really wonder what folks want from this flag in the first place.
>> It really tells you _nothing_.
> 
> 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).