Set and enforced VMPL in SNP attestation

.snpcc_canary

@@ -4,4 +4,4 @@
 /-xXx--//-----x=x--/-xXx--/---x---->>>--/
 ...
 /\/\d(-_-)b/\/\
-----
+----vmpl

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [6.0.0-dev3]
+
+[6.0.0-dev3]: https://github.com/microsoft/CCF/releases/tag/6.0.0-dev3
+
+### Changed
+
+- Set VMPL value when creating SNP attestations, and check VMPL value is in guest range when verifiying attestation, since recent [updates allow host-initiated attestations](https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/programmer-references/56860.pdf).
+
 ## [6.0.0-dev2]
 
 [6.0.0-dev2]: https://github.com/microsoft/CCF/releases/tag/6.0.0-dev2

include/ccf/pal/attestation.h

@@ -75,6 +75,16 @@ namespace ccf::pal
         fmt::format("SEV-SNP: Mask chip key must not be set"));
     }
 
+    // Introduced in https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/programmer-references/56860.pdf
+    // The guest sets the VMPL field to a value from 0 thru 3 which indicates a request from the guest.
+    // For a Guest requested attestation report this field will contain the value (0-3). A Host requested attestation report will have a value of 0xffffffff.
+    // CCF current always sets VMPL to 0, and rejects non-guest values.
+    if (quote.vmpl > 3)
+    {
+      throw std::logic_error(
+        fmt::format("SEV-SNP: VMPL for guest attestations must be in 0-3 range, not {}", quote.vmpl));
+    }
+
     report_data = SnpAttestationReportData(quote.report_data);
     measurement = SnpAttestationMeasurement(quote.measurement);
 

include/ccf/pal/snp_ioctl5.h

@@ -56,7 +56,7 @@ namespace ccf::pal::snp::ioctl5
   struct AttestationReq
   {
     uint8_t report_data[snp_attestation_report_data_size];
-    uint32_t vmpl;
+    uint32_t vmpl = 0;
     uint8_t reserved[28];
   };
 

include/ccf/pal/snp_ioctl6.h

@@ -23,7 +23,7 @@ namespace ccf::pal::snp::ioctl6
   struct AttestationReq
   {
     uint8_t report_data[snp_attestation_report_data_size];
-    uint32_t vmpl;
+    uint32_t vmpl = 0;
     uint8_t reserved[28]; // needs to be zero
   }; // aka snp_report_req in (linux) include/uapi/linux/sev-guest.h