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tpm-enrol: move NV cert index off OEM-occupied 0x01800001 → 0x01800100

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The Dell 820 kept "finding a cert" and bypassing enrolment despite repeated BIOS
TPM clears. tpm2_nvreadpublic revealed 0x01800001 on that hardware is a FIRMWARE
platform index (platformcreate|policydelete|writelocked, 70 bytes — not our
cert; siblings at 0x01800003/4 + 0x01810000). platformcreate survives TPM2_Clear
and policydelete needs the platform's secret policy, so it's permanent and
unusable by us — the blind check false-positived on it, and enrolment could
never write there anyway. Same class of bug as the EK-handle collision.

Move the NV cert index default 0x01800001 -> 0x01800100 (free on the 820, owner
range, overridable via rd.dot1x.nvindex): cmdline (extract-artifacts.sh),
fleet-enrol -nvindex, the dracut hooks, bench scripts, CLAUDE.md invariant #1,
and design/SSP docs. The signing-key handle (0x81000100) is unchanged.

Harden WriteNVCert: refuse a platformcreate index with a clear "pick a free
owner index via rd.dot1x.nvindex" error instead of a confusing undefine
failure. Regression simtest/TestWriteNVCertRefusesPlatformIndex; NV roundtrip +
ReadNVCert tests moved to 0x01800100. All go tests + packer validate pass.
This commit is contained in:
Audiobuzz
2026-07-03 02:51:38 +00:00
parent 33de300af8
commit 6fe623c727
16 changed files with 97 additions and 36 deletions
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files/enrol/tpmkey/tpmkey.go
+9 -1
View File
@@ -2,7 +2,7 @@
// / no openssl tpm2 provider). Provides: ensure a persistent ECDSA signing key
// at a non-reserved owner handle (default 0x81000100 — NOT the EK slot
// 0x81010001, see EnsureKey), a crypto.Signer backed by it (for CSR signing),
// and NV cert read-presence + write at 0x01800001. Talks to any transport.TPM,
// and NV cert read-presence + write at 0x01800100. Talks to any transport.TPM,
// so the same
// code runs against /dev/tpmrm0 (production) and the software simulator (tests).
//
@@ -224,6 +224,14 @@ func ReadNVCert(tpm transport.TPM, index tpm2.TPMHandle) ([]byte, error) {
func WriteNVCert(tpm transport.TPM, index tpm2.TPMHandle, der []byte) error {
// Undefine a stale index first (re-enrolment / resized cert).
if rp, err := (tpm2.NVReadPublic{NVIndex: index}).Execute(tpm); err == nil {
// A PLATFORM-created index at our handle is OEM firmware NV (bench-seen on
// a Dell 820: 0x01800001 was platformcreate|policydelete|writelocked). We
// cannot undefine it with owner auth, and TPM2_Clear/BIOS won't remove it —
// so fail LOUDLY with guidance rather than a confusing "nv undefine" error.
// The remedy is a different, free owner index via rd.dot1x.nvindex.
if pub, e := rp.NVPublic.Contents(); e == nil && pub.Attributes.PlatformCreate {
return fmt.Errorf("NV index %#x is a platform-created (firmware-owned) index — cannot be written by enrolment; pick a free owner index via rd.dot1x.nvindex / -nvindex", uint32(index))
}
if _, err := (tpm2.NVUndefineSpace{
AuthHandle: tpm2.TPMRHOwner,
NVIndex: tpm2.NamedHandle{Handle: index, Name: rp.NVName},