Re: [PATCH v8 27/40] x86/boot: Add Confidential Computing type to setup_data

Dave Hansen
2021-12-10T20:31:04Z

On 12/10/21 12:18 PM, Brijesh Singh wrote:
> On 12/10/21 1:12 PM, Dave Hansen wrote:
>> On 12/10/21 7:43 AM, Brijesh Singh wrote:
>>> +/* AMD SEV Confidential computing blob structure */
>>> +#define CC_BLOB_SEV_HDR_MAGIC 0x45444d41
>>> +struct cc_blob_sev_info {
>>> + u32 magic;
>>> + u16 version;
>>> + u16 reserved;
>>> + u64 secrets_phys;
>>> + u32 secrets_len;
>>> + u64 cpuid_phys;
>>> + u32 cpuid_len;
>>> +};
>> This is an ABI structure rather than some purely kernel construct, right?
>
> This is ABI between the guest BIOS and Guest OS. It is defined in the OVMF.
>
> https://github.com/tianocore/edk2/blob/master/OvmfPkg/Include/Guid/ConfidentialComputingSevSnpBlob.h
>
> SEV-SNP FW spec does not have it documented; it's up to the guest BIOS
> on how it wants to communicate the Secrets and CPUID page location to
> guest OS.

Well, no matter where it is defined, could we please make it a bit
easier for folks to find it in the future?

>> I searched through all of the specs to which you linked in the cover
>> letter. I looked for "blob", "guid", the magic and part of the GUID
>> itself trying to find where this is defined to see if the struct is correct.
>>
>> I couldn't find anything.
>>
>> Where is the spec for this blob? How large is it? Did you mean to
>> leave a 4-byte hole after secrets_len and before cpuid_phys?
> Yes, the length is never going to be > 4GB.

I was more concerned that this structure could change sizes if it were
compiled on 32-bit versus 64-bit code. For kernel ABIs, we try not to
do that.

Is this somehow OK when talking to firmware? Or can a 32-bit OS and
64-bit firmware never interact?