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attestation_policy: unify the PCR path across platforms #38

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attestation_policy: unify the PCR path across platforms #38

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38 changes: 35 additions & 3 deletions policy/attestation-policy.rego
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Original file line number Diff line number Diff line change
Expand Up @@ -29,10 +29,10 @@ default configuration := 36

##### Azure vTPM SNP
executables := 3 if {
platform := detect_platform
input.azsnpvtpm.measurement in data.reference.measurement
input.azsnpvtpm.tpm.pcr4 in data.reference.snp_pcr04
input.azsnpvtpm.tpm.pcr7 in data.reference.snp_pcr07
input.azsnpvtpm.tpm.pcr11 in data.reference.snp_pcr11
pcr_match(platform, "pcr04", data.reference.pcr04)
pcr_match(platform, "pcr07", data.reference.pcr07)
}

hardware := 2 if {
Expand All @@ -52,3 +52,35 @@ configuration := 2 if {
input.azsnpvtpm.policy_smt_allowed in data.reference.smt_allowed
}

##### PCRs check for any platform
platform_paths := {
"azure-snp": ["azsnpvtpm", "tpm"],
"azure-tdx": ["aztdxvtpm", "tpm"],
"raw": ["tpm"]
}

detect_platform := "azure-snp" if {
input.azsnpvtpm
} else := "azure-tdx" if {
input.aztdxvtpm
} else := "raw"

get_by_path(obj, path) = result if {
result := object.get(obj, path, false)
}

get_pcr_value(platform, pcr_name) = value if {
platform != "raw"
tpm := get_by_path(input, platform_paths[platform])
value := tpm[pcr_name]
}

get_pcr_value("raw", pcr_name) = value if {
tpm := get_by_path(input, platform_paths["raw"])
idx := to_number(trim_prefix(pcr_name, "pcr"))
value := tpm.pcr[idx]
}

pcr_match(platform, pcr_name, expected_values) if {
lower(get_pcr_value(platform, pcr_name)) in expected_values
}