Re: [PATCH v2 4/4] virt: Add sev_secret module to expose confidential computing secrets

From: Dov Murik <dovmurik@linux.ibm.com>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>
Cc: linux-efi@vger.kernel.org, Borislav Petkov <bp@suse.de>,
	Ashish Kalra <ashish.kalra@amd.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Andi Kleen <ak@linux.intel.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andrew Scull <ascull@google.com>,
	James Bottomley <jejb@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@linux.ibm.com>,
	Jim Cadden <jcadden@ibm.com>,
	Daniele Buono <dbuono@linux.vnet.ibm.com>,
	linux-coco@lists.linux.dev,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, Dov Murik <dovmurik@linux.ibm.com>
Subject: Re: [PATCH v2 4/4] virt: Add sev_secret module to expose confidential computing secrets
Date: Fri, 8 Oct 2021 08:40:14 +0300	[thread overview]
Message-ID: <fc31d2a9-ee56-f114-857e-310c4f4d7d4f@linux.ibm.com> (raw)
In-Reply-To: <YV8dsl+qgbIH6z8F@work-vm>

Thanks Dave and Dave for reviewing this.

On 07/10/2021 19:17, Dr. David Alan Gilbert wrote:
> * Dave Hansen (dave.hansen@intel.com) wrote:
>> On 10/6/21 11:18 PM, Dov Murik wrote:
>>> +static int sev_secret_map_area(void)
>>> +{
>>> +	struct sev_secret *s = sev_secret_get();
>>> +	struct linux_efi_coco_secret_area *secret_area;
>>> +	u32 secret_area_size;
>>> +
>>> +	if (efi.coco_secret == EFI_INVALID_TABLE_ADDR) {
>>> +		pr_err("Secret area address is not available\n");
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	secret_area = memremap(efi.coco_secret, sizeof(*secret_area), MEMREMAP_WB);
>>> +	if (secret_area == NULL) {
>>> +		pr_err("Could not map secret area header\n");
>>> +		return -ENOMEM;
>>> +	}
>>
>> There doesn't seem to be anything truly SEV-specific in here at all.
>> Isn't this more accurately called "efi_secret" or something?  What's to
>> prevent Intel or an ARM vendor from implementing this?
> 
> I don't think anything; although the last discussion I remember on list
> with Intel was that Intel preferred some interface with an ioctl to read
> the secrets and stuff.  I'm not quite sure if the attestation/secret
> delivery order makes sense with TDX, but if it does, then if you could
> persuade someone to standardise on this it would be great.
> 

I agree that this series doesn't have any SEV-specific stuff in it; in
fact, I wrote in the cover letter:

+++
This has been tested with AMD SEV and SEV-ES guests, but the kernel side
of handling the secret area has no SEV-specific dependencies, and
therefore might be usable (perhaps with minor changes) for any
confidential computing hardware that can publish the secret area via the
standard EFI config table entry.
+++

However, in previous rounds Boris said [1] that if it's only
hypothetical support for other platforms, I should add a
"depends on AMD_MEM_ENCRYPT" clause.  Boris, can you please share your view?

I'm indeed in favor of making this more generic (efi_secret sounds
good), allowing for future support for other early-boot secret injection
mechanisms.

[1] https://lore.kernel.org/linux-coco/YNojYBIwk0xCHQ0v@zn.tnic/

-Dov