diff options
Diffstat (limited to 'Documentation/security/vboot')
| -rw-r--r-- | Documentation/security/vboot/measured_boot.md | 83 |
1 files changed, 82 insertions, 1 deletions
diff --git a/Documentation/security/vboot/measured_boot.md b/Documentation/security/vboot/measured_boot.md index 3ec3729edf..45d66dd2d2 100644 --- a/Documentation/security/vboot/measured_boot.md +++ b/Documentation/security/vboot/measured_boot.md @@ -1,6 +1,8 @@ # Measured Boot coreboot measured boot is implemented as Google Verified Boot extension. This -means in order to use it, vboot needs to be available for your platform. +means in order to use it, vboot needs to be available for your platform. The +goal of this implementation is to implement an easy to understand and +transparent measured boot mechanism. ## IBB/CRTM The "Initial Boot Block" or "Core Root of Trust for Measurement" is the first @@ -21,10 +23,85 @@ measured boot extension because of platform constraints. The "Static Root of Trust for Measurement" is the easiest way doing measurements by measuring code before it is loaded. +### Measurements +SRTM mode measurements are done starting with the IBB as root of trust. +Only CBFS contents are measured at the moment. + +#### CBFS files (stages, blobs) +* CBFS data is measured as raw data before decompression happens. +* CBFS header is excluded from measurements. +* Measurements are stored in PCR 2. + +#### Runtime Data +* CBFS data which changes by external input dynamically. Never stays the same. +* It is identified by VBOOT_MEASURED_BOOT_RUNTIME_DATA kconfig option and + measured into a different PCR 3 in order to avoid PCR pre-calculation issues. + ![][srtm] [srtm]: srtm.png +### TCPA eventlog +coreboot makes use of its own TCPA log implementation. Normally the eventlog +specification can be found via the TCG homepage: + +[UEFI Specification](https://trustedcomputinggroup.org/resource/tcg-efi-platform-specification/) + +[BIOS Specification](https://www.trustedcomputinggroup.org/wp-content/uploads/TCG_PCClientImplementation_1-21_1_00.pdf) + +Both of them are not representing firmware measurements in a generalized way. +Therefore we have to implement our own solution. + +We decided to provide an easy to understand TCPA log which can be read out +from the operating system and firmware itself. + +#### Table Format +The first column describes the PCR index used for measurement. +The second column is the hash of the raw data. The third column contains +the hash algorithm used in the operation. The last column provides +information about what is measured. First the namespace from where the data +came from, CBFS or FMAP, then the name used to look up the data +(region or file name). + +#### Example: +```bash +PCR-2 e8f2b57c9ec5ea06d1bbd3240a753974d4c3e7c8cd305c20a8ea26eed906dc89 SHA256 [FMAP: COREBOOT CBFS: bootblock] +PCR-2 309a5fcb231d3a39127de2521792f332f9a69e05675ec52535d2dcded756dc19 SHA256 [FMAP: COREBOOT CBFS: fallback/verstage] +PCR-2 0fbba07a833d4dcfc7024eaf313661a0ba8f80a05c6d29b8801c612e10e60dee SHA256 [FMAP: RO_VPD] +PCR-2 431681113ed44cbf6f68a12c6e5687e901052f1d728a4777b2ad36e559962047 SHA256 [FMAP: GBB] +PCR-2 f47a8ec3e9aff2318d896942282ad4fe37d6391c82914f54a5da8a37de1300c6 SHA256 [FMAP: SI_DESC] +PCR-3 237f6f567f8597dbdff0a00690d34d21616af0dbe434b9a2d432b136c012765f SHA256 [FMAP: SI_ME] +PCR-2 7d2c7ac4888bfd75cd5f56e8d61f69595121183afc81556c876732fd3782c62f SHA256 [FMAP: SI_GBE] +PCR-0 62571891215b4efc1ceab744ce59dd0b66ea6f73 SHA1 [GBB flags] +PCR-1 a66c8c2cda246d332d0c2025b6266e1e23c89410051002f46bfad1c9265f43d0 SHA256 [GBB HWID] +PCR-2 ceca357524caf8fc73f5fa130f05a75293031962af884e18990d281eb259f5ff SHA256 [FMAP: FW_MAIN_B CBFS: fallback/romstage] +PCR-2 548a097604e0a975de76f98b04c7f0b0ddec03883dd69179e47a784704a1c571 SHA256 [FMAP: FW_MAIN_B CBFS: fspm.bin] +PCR-2 1e86b27008818244c221df2436b0113bd20a86ec6ec9d8259defe87f45d2f604 SHA256 [FMAP: FW_MAIN_B CBFS: spd2.bin] +PCR-2 05d78005fcfc9edd4ca5625f11b1f49991d17bdb7cee33b72e722bc785db55ae SHA256 [FMAP: FW_MAIN_B CBFS: fallback/postcar] +PCR-2 c13e95829af12a584046f1a6f3e1f6e4af691209324cfeeec573633399384141 SHA256 [FMAP: FW_MAIN_B CBFS: fallback/ramstage] +PCR-2 a6ec2761b597abd252dba2a7237140ef4a5a8e0d47cad8afb65fa16314413401 SHA256 [FMAP: FW_MAIN_B CBFS: cpu_microcode_blob.bin] +PCR-2 c81ffa40df0b6cd6cfde4f476d452a1f6f2217bc96a3b98a4fa4a037ee7039cf SHA256 [FMAP: FW_MAIN_B CBFS: fsps.bin] +PCR-2 4e95f57bbf3c6627eb1c72be9c48df3aaa8e6da4f5f63d85e554cf6803505609 SHA256 [FMAP: FW_MAIN_B CBFS: vbt.bin] +PCR-3 b7663f611ecf8637a59d72f623ae92a456c30377d4175e96021c85362f0323c8 SHA256 [FMAP: RW_NVRAM] +PCR-2 178561f046e2adbc621b12b47d65be82756128e2a1fe5116b53ef3637da700e8 SHA256 [FMAP: FW_MAIN_B CBFS: fallback/dsdt.aml] +PCR-2 091706f5fce3eb123dd9b96c15a9dcc459a694f5e5a86e7bf6064b819a8575c7 SHA256 [FMAP: FW_MAIN_B CBFS: fallback/payload] +``` + +#### Dump TCPA eventlog in the OS: +```bash +cbmem -L +``` + +#### Get CBFS file and print the hash +```bash +cbfstool coreboot.rom extract -r COREBOOT -n fallback/romstage -U -f /dev/stdout | sha256sum +``` + +#### Get FMAP partition and print the hash +```bash +cbfstool coreboot.rom read -n SI_ME -f /dev/stdout | sha256sum +``` + ## DRTM Mode The "Dynamic Root of Trust for Measurement" is realised by platform features like Intel TXT or Boot Guard. The features provide a way of loading a signed @@ -42,17 +119,21 @@ PCR-7 are left empty. ### PCR-0 _Hash:_ SHA1 + _Description:_ Google VBoot GBB flags. ### PCR-1 _Hash:_ SHA1/SHA256 + _Description:_ Google VBoot GBB HWID. ### PCR-2 _Hash:_ SHA1/SHA256 + _Description:_ Core Root of Trust for Measurement which includes all stages, data and blobs. ### PCR-3 _Hash:_ SHA1/SHA256 + _Description:_ Runtime data like hwinfo.hex or MRC cache. |