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

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Date:   Thu, 27 Oct 2022 10:57:32 +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 Thu, Oct 13, 2022 at 06:00:58PM -0300, Martin Fernandez wrote:
> That's bad, because it would be nice if that attribute only depended
> on the hardware and not on some setting.

Why would that be bad?

You want to be able to disable encryption for whatever reason sometimes.

> The plan of this patch was, as you mentioned just to report
> EFI_MEMORY_CPU_CRYPTO in a per node level.
> 
> Now, I think I will need to check for tme/sme and only if those are
> active then show the file in sysfs, otherwise not show it at all,
> because it would be misleading. Any other idea?

Well, I still think this is not going to work in all cases. SME/TME can
be enabled but the kernel can go - and for whatever reason - map a bunch
of memory unencrypted.

So I don't know what the goal of this fwupd checking whether users have
configured memory encryption properly is. It might end up giving that
false sense of security...

> You mean that EFI_MEMORY_CPU_CRYPTO means nothing on an AMD system?

I mean, you still can disable memory encryption.

-- 
Regards/Gruss,
    Boris.

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