Re: [PATCH] SUPPORT.md: split XSM from Flask

[Jan Beulich <jbeulich@xxxxxxxx>]

On 30.07.2024 14:35, Andrew Cooper wrote:
> On 30/07/2024 11:57 am, Jan Beulich wrote:
>> XSM is a generic framework, which in particular is also used by SILO.
>> With this it can't really be experimental: Arm enables SILO by default.
> 
> It's stronger than this.
> 
> XSA-295 makes SILO the only security supported configuration for ARM.

Okay, switched to "Arm mandates SILO for having a security supported
configuration."

>> --- a/SUPPORT.md
>> +++ b/SUPPORT.md
>> @@ -768,13 +768,20 @@ Compile time disabled for ARM by default
>>  
>>      Status, x86: Supported, not security supported
>>  
>> -### XSM & FLASK
>> +### XSM
>> +
>> +    Status: Supported
>> +
>> +See below for use with FLASK and SILO.  The dummy implementation is covered 
>> here
>> +as well.
> 
> This feels weird, although I can't suggest a better option.
> 
> XSM isn't optional; it can't be compiled out,

How can it not be? There's an "XSM" Kconfig control.

> nor can the dummy policy,

In a way. Yet how the dummy policy is instantiated is quite different
between XSM=y and XSM=n.

> so it's weird to call out what literally cannot have a statement
> different to the rest of Xen.
> 
> Combined with ...
> 
>> +
>> +### XSM + FLASK
> 
> ... this wanting to say "Flask (XSM module/policy)" IMO, maybe what we
> really want is:
> 
> ---%<---
> ### XSM (Xen Security Modules)
> 
> Base XSM is a security policy framework used in Xen.  The dummy policy
> implements a basic "dom0 all powerful, domUs all unprivileged" policy".
> ---%<---
> 
> intentionally without giving a Status.

As per above, imo XSM=y wants security status named. That's, after all,
part of what was missing / ambiguous so far.

> Then, the two blocks below are clearly alternative modules which have
> optionality and different support statuses.

I'll change the wording there some, to be closer to what you and also
Daniel ask for.

Jan