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From:   Martin Fernandez <martin.fernandez@eclypsium.com>
Date:   Wed, 4 May 2022 14:18:30 -0300
Message-ID: <CAKgze5YDD02AsrF0yESv2sptZ4qxyTMgCDmnOKcbQWjKQsJRsw@mail.gmail.com>
Subject: Re: [PATCH v8 0/8] x86: Show in sysfs if a memory node is able to do encryption
To:     Borislav Petkov <bp@alien8.de>
Cc:     linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org,
        platform-driver-x86@vger.kernel.org, linux-mm@kvack.org,
        tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com,
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        alison.schofield@intel.com, keescook@chromium.org
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On 5/4/22, Borislav Petkov <bp@alien8.de> wrote:
> On Fri, Apr 29, 2022 at 05:17:09PM -0300, Martin Fernandez wrote:
>> Show for each node if every memory descriptor in that node has the
>> EFI_MEMORY_CPU_CRYPTO attribute.
>>
>> fwupd project plans to use it as part of a check to see if the users
>> have properly configured memory hardware encryption
>> capabilities. fwupd's people have seen cases where it seems like there
>> is memory encryption because all the hardware is capable of doing it,
>> but on a closer look there is not, either because of system firmware
>> or because some component requires updating to enable the feature.
>
> Hm, so in the sysfs patch you have:
>
> +               This value is 1 if all system memory in this node is
> +               capable of being protected with the CPU's memory
> +               cryptographic capabilities.
>
> So this says the node is capable - so what is fwupd going to report -
> that the memory is capable?
>
> From your previous paragraph above it sounds to me like you wanna
> say whether memory encryption is active or not, not that the node is
> capable.
>
> Or what is the use case?

The use case is to know if a user is using hardware encryption or
not. This new sysfs file plus knowing if tme/sev is active you can be
pretty sure about that.

>> It's planned to make it part of a specification that can be passed to
>> people purchasing hardware
>
> So people are supposed to run that fwupd on that new hw to check whether
> they can use memory encryption?

Yes

>> These checks will run at every boot. The specification is called Host
>> Security ID: https://fwupd.github.io/libfwupdplugin/hsi.html.
>>
>> We choosed to do it a per-node basis because although an ABI that
>> shows that the whole system memory is capable of encryption would be
>> useful for the fwupd use case, doing it in a per-node basis gives also
>> the capability to the user to target allocations from applications to
>> NUMA nodes which have encryption capabilities.
>
> That's another hmmm: what systems do not do full system memory
> encryption and do only per-node?
>
> From those I know, you encrypt the whole memory on the whole system and
> that's it. Even if it is a hypervisor which runs a lot of guests, you
> still want the hypervisor itself to run encrypted, i.e., what's called
> SME in AMD's variant.

Dave Hansen pointed those out in a previuos patch serie, here is the
quote:

> CXL devices will have normal RAM on them, be exposed as "System RAM" and
> they won't have encryption capabilities.  I think these devices were
> probably the main motivation for EFI_MEMORY_CPU_CRYPTO.