path: root/Documentation/security
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authorLinus Torvalds <>2019-09-17 16:22:26 -0700
committerLinus Torvalds <>2019-09-17 16:22:26 -0700
commit7c672abc120a55f678e5571ae2ee93f06ca4d7f9 (patch)
tree7beebc09f9626ca8d5f7df4dded0a553de479323 /Documentation/security
parent1902314157b19754e0ff25b44527654847cfd127 (diff)
parentfe013f8bc160d79c6e33bb66d9bb0cd24949274c (diff)
Merge tag 'docs-5.4' of git://
Pull documentation updates from Jonathan Corbet: "It's a somewhat calmer cycle for docs this time, as the churn of the mass RST conversion is happily mostly behind us. - A new document on reproducible builds. - We finally got around to zapping the documentation for hardware support that was removed in 2004; one doesn't want to rush these things. - The usual assortment of fixes, typo corrections, etc" * tag 'docs-5.4' of git:// (67 commits) Documentation: kbuild: Add document about reproducible builds docs: printk-formats: Stop encouraging use of unnecessary %h[xudi] and %hh[xudi] Documentation: Add "earlycon=sbi" to the admin guide doc:lock: remove reference to clever use of read-write lock devices.txt: improve entry for comedi (char major 98) docs: mtd: Update spi nor reference driver doc: arm64: fix grammar dtb placed in no attributes region Documentation: sysrq: don't recommend 'S' 'U' before 'B' mailmap: Update email address for Quentin Perret docs: ftrace: clarify when tracing is disabled by the trace file docs: process: fix broken link Documentation/arm/samsung-s3c24xx: Remove stray U+FEFF character to fix title Documentation/arm/sa1100/assabet: Fix 'make assabet_defconfig' command Documentation/arm/sa1100: Remove some obsolete documentation docs/zh_CN: update Chinese howto.rst for latexdocs making Documentation: virt: Fix broken reference to virt tree's index docs: Fix typo on pull requests guide kernel-doc: Allow anonymous enum Documentation: sphinx: Don't parse socket() as identifier reference Documentation: sphinx: Add missing comma to list of strings ...
Diffstat (limited to 'Documentation/security')
2 files changed, 56 insertions, 0 deletions
diff --git a/Documentation/security/tpm/index.rst b/Documentation/security/tpm/index.rst
index 487852fda33e..fc40e9f23c85 100644
--- a/Documentation/security/tpm/index.rst
+++ b/Documentation/security/tpm/index.rst
@@ -4,6 +4,7 @@ Trusted Platform Module documentation
.. toctree::
+ tpm_event_log
diff --git a/Documentation/security/tpm/tpm_event_log.rst b/Documentation/security/tpm/tpm_event_log.rst
new file mode 100644
index 000000000000..f00f7a1d5e92
--- /dev/null
+++ b/Documentation/security/tpm/tpm_event_log.rst
@@ -0,0 +1,55 @@
+.. SPDX-License-Identifier: GPL-2.0
+TPM Event Log
+This document briefly describes what TPM log is and how it is handed
+over from the preboot firmware to the operating system.
+The preboot firmware maintains an event log that gets new entries every
+time something gets hashed by it to any of the PCR registers. The events
+are segregated by their type and contain the value of the hashed PCR
+register. Typically, the preboot firmware will hash the components to
+who execution is to be handed over or actions relevant to the boot
+The main application for this is remote attestation and the reason why
+it is useful is nicely put in the very first section of [1]:
+"Attestation is used to provide information about the platform’s state
+to a challenger. However, PCR contents are difficult to interpret;
+therefore, attestation is typically more useful when the PCR contents
+are accompanied by a measurement log. While not trusted on their own,
+the measurement log contains a richer set of information than do the PCR
+contents. The PCR contents are used to provide the validation of the
+measurement log."
+UEFI event log
+UEFI provided event log has a few somewhat weird quirks.
+Before calling ExitBootServices() Linux EFI stub copies the event log to
+a custom configuration table defined by the stub itself. Unfortunately,
+the events generated by ExitBootServices() don't end up in the table.
+The firmware provides so called final events configuration table to sort
+out this issue. Events gets mirrored to this table after the first time
+EFI_TCG2_PROTOCOL.GetEventLog() gets called.
+This introduces another problem: nothing guarantees that it is not called
+before the Linux EFI stub gets to run. Thus, it needs to calculate and save the
+final events table size while the stub is still running to the custom
+configuration table so that the TPM driver can later on skip these events when
+concatenating two halves of the event log from the custom configuration table
+and the final events table.
+- [1]
+- [2] The final concatenation is done in drivers/char/tpm/eventlog/efi.c