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;
IronPort-SDR: bBxUbdwyVW6kWjdtq2MYHIV24VKQeddX7RODMW9hZdFqJZ0ZEk4bVIvJnQkOFt7swK6qibkUCS
 fHtdgd4+ySmw==
IronPort-SDR: wWwwSMERFTz9/ebtIv2uP4Ew5ChxpDuaT34KfgKOffFPzRqXckZ+FvQj2Nkpn1rBPjHPfAs8uO
 hp5+wXuKDp0w==
Subject: Re: [PATCH] Ability to read the MKTME status from userspace
To:     Richard Hughes <hughsient@gmail.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>
References: <20200618210215.23602-1-daniel.gutson@eclypsium.com>
 <589c89ae-620e-36f8-2be5-4afc727c2911@intel.com>
 <CAFmMkTHNxSN_uWtm63TdkGxj44NXQQKEOmATXhjA=4DSCS92kQ@mail.gmail.com>
 <23babf62-00cb-cb47-bb19-da9508325934@intel.com>
 <CAD2FfiFbGdf5uKmsc14F4ZuuCUQYFwfnirn=Y0fu2F0=njvWug@mail.gmail.com>
 <80578b72-cb6f-8da9-1043-b4055c75d7f6@intel.com>
 <CAD2FfiG1BgYvR6wkeXGro8v6FQtVjKemmAOOf2W14z5KUWLqhw@mail.gmail.com>
 <d55f94bc-3b26-a556-f7e6-43e9b1007e13@intel.com>
 <CAD2FfiHCi2MfShGWaYWk_GcXW4xVr6chsLPZs78OJE+2_GErVg@mail.gmail.com>
 <3d454068-fd4e-4399-4bf5-2d010bb2ba7d@intel.com>
 <CAD2FfiF8QEarhyFD1GkfnaR+spyH86sChgRZm37ab_gzS2m_wg@mail.gmail.com>
From:   Dave Hansen <dave.hansen@intel.com>
Autocrypt: addr=dave.hansen@intel.com; keydata=
 xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC
 oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY
 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb
 ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz
 VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W
 iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn
 c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1
 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb
 ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL
 QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzShEYXZpZCBDaHJp
 c3RvcGhlciBIYW5zZW4gPGRhdmVAc3I3MS5uZXQ+wsF7BBMBAgAlAhsDBgsJCAcDAgYVCAIJ
 CgsEFgIDAQIeAQIXgAUCTo3k0QIZAQAKCRBoNZUwcMmSsMO2D/421Xg8pimb9mPzM5N7khT0
 2MCnaGssU1T59YPE25kYdx2HntwdO0JA27Wn9xx5zYijOe6B21ufrvsyv42auCO85+oFJWfE
 K2R/IpLle09GDx5tcEmMAHX6KSxpHmGuJmUPibHVbfep2aCh9lKaDqQR07gXXWK5/yU1Dx0r
 VVFRaHTasp9fZ9AmY4K9/BSA3VkQ8v3OrxNty3OdsrmTTzO91YszpdbjjEFZK53zXy6tUD2d
 e1i0kBBS6NLAAsqEtneplz88T/v7MpLmpY30N9gQU3QyRC50jJ7LU9RazMjUQY1WohVsR56d
 ORqFxS8ChhyJs7BI34vQusYHDTp6PnZHUppb9WIzjeWlC7Jc8lSBDlEWodmqQQgp5+6AfhTD
 kDv1a+W5+ncq+Uo63WHRiCPuyt4di4/0zo28RVcjtzlGBZtmz2EIC3vUfmoZbO/Gn6EKbYAn
 rzz3iU/JWV8DwQ+sZSGu0HmvYMt6t5SmqWQo/hyHtA7uF5Wxtu1lCgolSQw4t49ZuOyOnQi5
 f8R3nE7lpVCSF1TT+h8kMvFPv3VG7KunyjHr3sEptYxQs4VRxqeirSuyBv1TyxT+LdTm6j4a
 mulOWf+YtFRAgIYyyN5YOepDEBv4LUM8Tz98lZiNMlFyRMNrsLV6Pv6SxhrMxbT6TNVS5D+6
 UorTLotDZKp5+M7BTQRUY85qARAAsgMW71BIXRgxjYNCYQ3Xs8k3TfAvQRbHccky50h99TUY
 sqdULbsb3KhmY29raw1bgmyM0a4DGS1YKN7qazCDsdQlxIJp9t2YYdBKXVRzPCCsfWe1dK/q
 66UVhRPP8EGZ4CmFYuPTxqGY+dGRInxCeap/xzbKdvmPm01Iw3YFjAE4PQ4hTMr/H76KoDbD
 cq62U50oKC83ca/PRRh2QqEqACvIH4BR7jueAZSPEDnzwxvVgzyeuhwqHY05QRK/wsKuhq7s
 UuYtmN92Fasbxbw2tbVLZfoidklikvZAmotg0dwcFTjSRGEg0Gr3p/xBzJWNavFZZ95Rj7Et
 db0lCt0HDSY5q4GMR+SrFbH+jzUY/ZqfGdZCBqo0cdPPp58krVgtIGR+ja2Mkva6ah94/oQN
 lnCOw3udS+Eb/aRcM6detZr7XOngvxsWolBrhwTQFT9D2NH6ryAuvKd6yyAFt3/e7r+HHtkU
 kOy27D7IpjngqP+b4EumELI/NxPgIqT69PQmo9IZaI/oRaKorYnDaZrMXViqDrFdD37XELwQ
 gmLoSm2VfbOYY7fap/AhPOgOYOSqg3/Nxcapv71yoBzRRxOc4FxmZ65mn+q3rEM27yRztBW9
 AnCKIc66T2i92HqXCw6AgoBJRjBkI3QnEkPgohQkZdAb8o9WGVKpfmZKbYBo4pEAEQEAAcLB
 XwQYAQIACQUCVGPOagIbDAAKCRBoNZUwcMmSsJeCEACCh7P/aaOLKWQxcnw47p4phIVR6pVL
 e4IEdR7Jf7ZL00s3vKSNT+nRqdl1ugJx9Ymsp8kXKMk9GSfmZpuMQB9c6io1qZc6nW/3TtvK
 pNGz7KPPtaDzvKA4S5tfrWPnDr7n15AU5vsIZvgMjU42gkbemkjJwP0B1RkifIK60yQqAAlT
 YZ14P0dIPdIPIlfEPiAWcg5BtLQU4Wg3cNQdpWrCJ1E3m/RIlXy/2Y3YOVVohfSy+4kvvYU3
 lXUdPb04UPw4VWwjcVZPg7cgR7Izion61bGHqVqURgSALt2yvHl7cr68NYoFkzbNsGsye9ft
 M9ozM23JSgMkRylPSXTeh5JIK9pz2+etco3AfLCKtaRVysjvpysukmWMTrx8QnI5Nn5MOlJj
 1Ov4/50JY9pXzgIDVSrgy6LYSMc4vKZ3QfCY7ipLRORyalFDF3j5AGCMRENJjHPD6O7bl3Xo
 4DzMID+8eucbXxKiNEbs21IqBZbbKdY1GkcEGTE7AnkA3Y6YB7I/j9mQ3hCgm5muJuhM/2Fr
 OPsw5tV/LmQ5GXH0JQ/TZXWygyRFyyI2FqNTx4WHqUn3yFj8rwTAU1tluRUYyeLy0ayUlKBH
 ybj0N71vWO936MqP6haFERzuPAIpxj2ezwu0xb1GjTk4ynna6h5GjnKgdfOWoRtoWndMZxbA
 z5cecg==
Message-ID: <aef4ff03-3a98-4425-2b01-203a88401370@intel.com>
Date:   Fri, 19 Jun 2020 07:48:55 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.8.0
MIME-Version: 1.0
In-Reply-To: <CAD2FfiF8QEarhyFD1GkfnaR+spyH86sChgRZm37ab_gzS2m_wg@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 6/19/20 7:36 AM, Richard Hughes wrote:
> 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?

Of course!  Just like AVX-512 or VNNI or whatever, Intel will totally
tell you about the stuff baked into its silicon!  But, just like
AVX-512, there's a lot of work to do on top of mere presence in the
silicon to ensure it is providing benefit.

>>> 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.

You cut out the important part.  The "pretty sure" involves a bunch of
preconditions and knowing what your hardware configuration is in the
first place.

Let's take a step back.  We add read-only ABIs so that decisions can be
made.  What decision will somebody make from the ABI being proposed here?

Someone does 'cat /proc/mktme' (or whatever) and it says "1" or
whatever, which means yay, encryption is on.  What do they do?

What do they do differently when it says "0"?