linux-kernel - Re: [PATCH v9 0/9] x86: Show in sysfs if a memory node is able to do encryption

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Message-ID: <Y0hrhzprPFTK+VWV@zn.tnic>
Date:   Thu, 13 Oct 2022 21:48:23 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Martin Fernandez <martin.fernandez@...ypsium.com>
Cc:     linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, linux-mm@...ck.org,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, ardb@...nel.org,
        dvhart@...radead.org, andy@...radead.org,
        gregkh@...uxfoundation.org, rafael@...nel.org, rppt@...nel.org,
        akpm@...ux-foundation.org, daniel.gutson@...ypsium.com,
        hughsient@...il.com, alex.bazhaniuk@...ypsium.com,
        alison.schofield@...el.com, keescook@...omium.org
Subject: Re: [PATCH v9 0/9] x86: Show in sysfs if a memory node is able to do
 encryption

On Mon, Jul 04, 2022 at 10:58:24AM -0300, Martin Fernandez wrote:
> If all nodes are capable of encryption and if the system have tme/sme
> on we can pretty confidently say that the device is actively
> encrypting all its memory.

Wait, what?

If all memory is crypto capable and I boot with mem_encrypt=off, then
the device is certainly not encrypting any memory.

dhansen says TME cannot be controlled this way and if you turn it off in
the BIOS, EFI_MEMORY_CPU_CRYPTO attr should not be set either. But that
marking won't work on AMD.

You really need to be able to check whether memory encryption is also
enabled.

And I believe I've said this before but even if encryption is on, it is
never "all its memory": the machine can decide to decrypt a page or a
bunch of them for whatever reason. And then they're plaintext.

> It's planned to make this check part of an specification that can be
> passed to people purchasing hardware

How is that supposed to work?

People would boot a Linux on that hardware and fwupd would tell them
whether it can encrypt memory or not?

But if that were the only use case, why can't EFI simply say that in its
fancy GUI?

Because all the kernel seems to be doing here is parrot further
EFI_MEMORY_CPU_CRYPTO.

And that attribute gets set by EFI so it goes and picks apart whether
the underlying hw can encrypt memory. So EFI could report it too.

Hmmm?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette