Detect TDX Guest when it's virtualised using Hyper-V

[fidencio]

Microsoft has decided to purposefully hide the information of the guest TEE when VMs are being created using Hyper-V.

This leads us to check for the Hyper-V cpuid features (0x4000000C), and then for the ebx value set.

For Intel TDX, ebx is set as 0xbe3, being 3 the part we're mostly interested about,according to:
https://github.com/torvalds/linux/blob/d2f51b3516dade79269ff45eae2a7668ae711b25/arch/x86/include/asm/hyperv-tlfs.h#L169-L174

[fidencio]

Here's the test that I've done on a TDX Guest using this PR:

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ git rev-parse --short HEAD
21e1a5b

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ git clean -xfd

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ go build

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ ./cpuid | grep -o TDX_GUEST

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ git reset --hard fidencio/topic/add-tdx-guest-detection
HEAD is now at 3224975 Detect TDX Guest when it's virtualised using Hyper-V

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ git rev-parse --short HEAD
3224975

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ git clean -xfd
Removing cpuid

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ go build

intel-coco@tdvm:~/fidencio/cpuid/cmd/cpuid$ ./cpuid | grep -o TDX_GUEST
TDX_GUEST

[fidencio]

Wow, it seems I need to adapt the tests, @klauspost, I'd appreciate a pointer here.

[klauspost]

LGTM

[fidencio]

Thanks @klauspost, do you think we can have a new release of the project soon enough?
I'd like to get this into Node Feature Discovery.

[klauspost]

Sure thing. Cut https://github.com/klauspost/cpuid/releases/tag/v2.2.6

[fidencio]

Sure thing. Cut https://github.com/klauspost/cpuid/releases/tag/v2.2.6

Thanks a lot, I've opened #139 as a way to say "thank you for all the work!" (unfortunately it gives your more work, but that's life). :-)