| Message ID | 20220217110059.2320497-1-dovmurik@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] docs/system/i386: Add measurement calculation details to amd-memory-encryption | expand |
* Dov Murik (dovmurik@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 <dovmurik@linux.ibm.com> > Suggested-by: Daniel P. Berrangé <berrange@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 <dgilbert@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 >
Queued, thanks. Paolo
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:
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 <dovmurik@linux.ibm.com> Suggested-by: Daniel P. Berrangé <berrange@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(-) base-commit: c13b8e9973635f34f3ce4356af27a311c993729c