* Dov Murik (dovmu...@linux.ibm.com) wrote: > Add a section explaining how the Guest Owner should calculate the > expected guest launch measurement for SEV and SEV-ES. > > Also update the name and links to the SEV API Spec document. > > Signed-off-by: Dov Murik <dovmu...@linux.ibm.com> > Suggested-by: Daniel P. Berrangé <berra...@redhat.com> >
Thanks; my guess is we're going to need to document the expected VMSA values at some point. Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > --- > > v2: > - Explain that firmware must be built without NVRAM store. > > v3: > - rstify > --- > docs/system/i386/amd-memory-encryption.rst | 54 ++++++++++++++++++++-- > 1 file changed, 50 insertions(+), 4 deletions(-) > > diff --git a/docs/system/i386/amd-memory-encryption.rst > b/docs/system/i386/amd-memory-encryption.rst > index 215946f813..dcf4add0e7 100644 > --- a/docs/system/i386/amd-memory-encryption.rst > +++ b/docs/system/i386/amd-memory-encryption.rst > @@ -47,7 +47,7 @@ The guest policy is passed as plaintext. A hypervisor may > choose to read it, > but should not modify it (any modification of the policy bits will result > in bad measurement). The guest policy is a 4-byte data structure containing > several flags that restricts what can be done on a running SEV guest. > -See KM Spec section 3 and 6.2 for more details. > +See SEV API Spec ([SEVAPI]_) section 3 and 6.2 for more details. > > The guest policy can be provided via the ``policy`` property:: > > @@ -92,7 +92,7 @@ expects. > ``LAUNCH_FINISH`` finalizes the guest launch and destroys the cryptographic > context. > > -See SEV KM API Spec ([SEVKM]_) 'Launching a guest' usage flow (Appendix A) > for the > +See SEV API Spec ([SEVAPI]_) 'Launching a guest' usage flow (Appendix A) for > the > complete flow chart. > > To launch a SEV guest:: > @@ -118,6 +118,49 @@ a SEV-ES guest: > - Requires in-kernel irqchip - the burden is placed on the hypervisor to > manage booting APs. > > +Calculating expected guest launch measurement > +--------------------------------------------- > + > +In order to verify the guest launch measurement, The Guest Owner must compute > +it in the exact same way as it is calculated by the AMD-SP. SEV API Spec > +([SEVAPI]_) section 6.5.1 describes the AMD-SP operations: > + > + GCTX.LD is finalized, producing the hash digest of all plaintext data > + imported into the guest. > + > + The launch measurement is calculated as: > + > + HMAC(0x04 || API_MAJOR || API_MINOR || BUILD || GCTX.POLICY || GCTX.LD > || MNONCE; GCTX.TIK) > + > + where "||" represents concatenation. > + > +The values of API_MAJOR, API_MINOR, BUILD, and GCTX.POLICY can be obtained > +from the ``query-sev`` qmp command. > + > +The value of MNONCE is part of the response of ``query-sev-launch-measure``: > it > +is the last 16 bytes of the base64-decoded data field (see SEV API Spec > +([SEVAPI]_) section 6.5.2 Table 52: LAUNCH_MEASURE Measurement Buffer). > + > +The value of GCTX.LD is > +``SHA256(firmware_blob || kernel_hashes_blob || vmsas_blob)``, where: > + > +* ``firmware_blob`` is the content of the entire firmware flash file (for > + example, ``OVMF.fd``). Note that you must build a stateless firmware file > + which doesn't use an NVRAM store, because the NVRAM area is not measured, > and > + therefore it is not secure to use a firmware which uses state from an NVRAM > + store. > +* if kernel is used, and ``kernel-hashes=on``, then ``kernel_hashes_blob`` is > + the content of PaddedSevHashTable (including the zero padding), which > itself > + includes the hashes of kernel, initrd, and cmdline that are passed to the > + guest. The PaddedSevHashTable struct is defined in ``target/i386/sev.c``. > +* if SEV-ES is enabled (``policy & 0x4 != 0``), ``vmsas_blob`` is the > + concatenation of all VMSAs of the guest vcpus. Each VMSA is 4096 bytes > long; > + its content is defined inside Linux kernel code as ``struct > vmcb_save_area``, > + or in AMD APM Volume 2 ([APMVOL2]_) Table B-2: VMCB Layout, State Save > Area. > + > +If kernel hashes are not used, or SEV-ES is disabled, use empty blobs for > +``kernel_hashes_blob`` and ``vmsas_blob`` as needed. > + > Debugging > --------- > > @@ -142,8 +185,11 @@ References > `AMD Memory Encryption whitepaper > > <https://developer.amd.com/wordpress/media/2013/12/AMD_Memory_Encryption_Whitepaper_v7-Public.pdf>`_ > > -.. [SEVKM] `Secure Encrypted Virtualization Key Management > - > <http://developer.amd.com/wordpress/media/2017/11/55766_SEV-KM-API_Specification.pdf>`_ > +.. [SEVAPI] `Secure Encrypted Virtualization API > + > <https://www.amd.com/system/files/TechDocs/55766_SEV-KM_API_Specification.pdf>`_ > + > +.. [APMVOL2] `AMD64 Architecture Programmer's Manual Volume 2: System > Programming > + <https://www.amd.com/system/files/TechDocs/24593.pdf>`_ > > KVM Forum slides: > > > base-commit: c13b8e9973635f34f3ce4356af27a311c993729c > -- > 2.25.1 > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
