linux-kernel - Re: [PATCH v1 04/26] x86/sev: Add the host SEV-SNP initialization support

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Date: Tue, 9 Jan 2024 13:44:40 +0100
From: Borislav Petkov <bp@...en8.de>
To: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
Cc: Michael Roth <michael.roth@....com>, x86@...nel.org,
	kvm@...r.kernel.org, linux-coco@...ts.linux.dev, linux-mm@...ck.org,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, jroedel@...e.de,
	thomas.lendacky@....com, hpa@...or.com, ardb@...nel.org,
	pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
	jmattson@...gle.com, luto@...nel.org, dave.hansen@...ux.intel.com,
	slp@...hat.com, pgonda@...gle.com, peterz@...radead.org,
	srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
	tobin@....com, vbabka@...e.cz, kirill@...temov.name,
	ak@...ux.intel.com, tony.luck@...el.com,
	sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
	jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com,
	pankaj.gupta@....com,
	"liam.merwick@...cle.com Brijesh Singh" <brijesh.singh@....com>
Subject: Re: [PATCH v1 04/26] x86/sev: Add the host SEV-SNP initialization
 support

On Tue, Jan 09, 2024 at 01:29:06PM +0100, Borislav Petkov wrote:
> At least three issues I see with that:
> 
> - the allocation can fail so it is a lot more convenient when the
>   firmware prepares it
> 
> - the RMP_BASE and RMP_END writes need to be verified they actially did
>   set up the RMP range because if they haven't, you might as well
>   throw SNP security out of the window. In general, letting the kernel
>   do the RMP allocation needs to be verified very very thoroughly.
> 
> - a future feature might make this more complicated

- What do you do if you boot on a system which has the RMP already
  allocated in the BIOS?

- How do you detect that it is the L1 kernel that must allocate the RMP?

- Why can't you use the BIOS allocated RMP in your scenario too instead
  of the L1 kernel allocating it?

- ...

I might think of more.

-- 
Regards/Gruss,
    Boris.

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