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 link to the SEV API Spec document.
Signed-off-by: Dov Murik <dovmu...@linux.ibm.com>
Suggested-by: Daniel P. Berrangé <berra...@redhat.com>
---
docs/amd-memory-encryption.txt | 50 +++++++++++++++++++++++++++++++---
1 file changed, 46 insertions(+), 4 deletions(-)
diff --git a/docs/amd-memory-encryption.txt b/docs/amd-memory-encryption.txt
index ffca382b5f..f97727482f 100644
--- a/docs/amd-memory-encryption.txt
+++ b/docs/amd-memory-encryption.txt
@@ -43,7 +43,7 @@ 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 [1] section 3 and 6.2 for more details.
The guest policy can be provided via the 'policy' property (see below)
@@ -88,7 +88,7 @@ expects.
LAUNCH_FINISH finalizes the guest launch and destroys the cryptographic
context.
-See SEV KM API Spec [1] 'Launching a guest' usage flow (Appendix A) for the
+See SEV API Spec [1] 'Launching a guest' usage flow (Appendix A) for the
complete flow chart.
To launch a SEV guest
@@ -113,6 +113,45 @@ 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 [1]
+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 [1]
+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).
+* 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 [2] 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
-----------
Since the memory contents of a SEV guest are encrypted, hypervisor access to
@@ -134,8 +173,11 @@ References
AMD Memory Encryption whitepaper:
https://developer.amd.com/wordpress/media/2013/12/AMD_Memory_Encryption_Whitepaper_v7-Public.pdf
-Secure Encrypted Virtualization Key Management:
-[1]
http://developer.amd.com/wordpress/media/2017/11/55766_SEV-KM-API_Specification.pdf
+Secure Encrypted Virtualization API:
+[1]
https://www.amd.com/system/files/TechDocs/55766_SEV-KM_API_Specification.pdf
+
+AMD64 Architecture Programmer's Manual Volume 2: System Programming
+[2] https://www.amd.com/system/files/TechDocs/24593.pdf
KVM Forum slides:
http://www.linux-kvm.org/images/7/74/02x08A-Thomas_Lendacky-AMDs_Virtualizatoin_Memory_Encryption_Technology.pdf
base-commit: a3607def89f9cd68c1b994e1030527df33aa91d0
--
2.25.1
