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TBSIMP_E_NO_EVENT_LOG
The decisive TPM checkpoint
TBSIMP_E_NO_EVENT_LOG (0x8029021B) belongs to the measured-boot event-log path. The base What Is page already shows the short Windows message; the additional diagnostic value is that this result marks TBS cannot obtain the TCG measured-boot event log expected from the platform.
The first producer to identify for it is TBS retrieval of the Windows Boot Configuration Log or TCG event log. The Windows Boot Configuration Log records measured-boot events that explain PCR extensions. TBS retrieves that firmware/platform artifact; it does not synthesize the history from the TPM after the fact.
Before changing the platform
| Question | Evidence for it |
|---|---|
| What exact state was rejected? | TBS cannot obtain the TCG measured-boot event log expected from the platform |
| Which layer owns the result? | TBS retrieval of the Windows Boot Configuration Log or TCG event log. |
| What must be correlated? | Tbsi_Get_TCG_Log or _Ex result, requested log type, firmware/UEFI mode, Secure Boot and measured-boot state, TBS event ID, and BIOS revision |
| What is the controlled comparison? | query the log size with the documented API and compare after a normal cold boot without clearing the TPM |
A useful this result trace links three code-specific timelines: the application call, the local TBS/provider or firmware event, and the raw command/response exchange. The result timestamps should describe one attempt; combining data from separate retries is particularly misleading for authorization sessions, context counters, DAA stages and lockout state.
Test the contract
The one-variable check is to query the log size with the documented API and compare after a normal cold boot without clearing the TPM. Record the before/after state that the result command is allowed to change. If the operation can have side effects, use a disposable key, session, counter or NV index rather than production material.
- Capture this result and
0x8029021Bat the first code-specific return boundary. - Decode the result state: requested log type, firmware exposure, output size, boot mode, event source and BIOS revision.
- Run the result controlled comparison once and preserve both binary transcripts.
- Verify the expected this result output or state transition instead of relying on absence of a UI message.
Why another code is not equivalent
| Comparison code | Built-in distinction |
|---|---|
TPM_E_ERROR_MASK | This is an error mask to convert TPM hardware errors to win errors — a separate checkpoint when compared with it. |
TPM_E_FAIL | The operation failed — a separate checkpoint when compared with it. |
TPM_E_SHA_THREAD | There is no existing SHA-1 thread — a separate checkpoint when compared with it. |
It specifically answers whether TBS cannot obtain the TCG measured-boot event log expected from the platform. In contrast, a valid event log explains PCR extensions, whereas PCR values alone cannot reconstruct missing event records.
Evidence of success
To remediate it, update firmware or platform configuration so it exposes the WBCL/TCG log; do not synthesize a log from PCR values. Do not manufacture an event log from final PCR values. PCRs contain cumulative measurements but cannot recover event order, event payloads or all digest banks.
After correcting it, start with a fresh caller context where the protocol requires one, replay the original intended operation, and confirm that hardware-backed policy remains enforced.
Authoritative references
- Microsoft: Tbsi_Get_TCG_Log — source for the checkpoint.
- Microsoft: Tbsi_Get_TCG_Log_Ex — source for the checkpoint.
- Microsoft: TBS functions — source for the checkpoint.
- TCG: PC Client Platform TPM Profile — source for the checkpoint.
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