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authorPatrick Rudolph <patrick.rudolph@9elements.com>2020-02-27 14:55:50 +0100
committerPatrick Rudolph <siro@das-labor.org>2020-04-27 08:52:52 +0000
commitfcfca1da5ea4eee266c830948ec117f06a3553cd (patch)
tree5ad3ee739a343f4ccee299d8e3a66d528e4207ce /Documentation/mainboard
parent34d9e68ff9026496fb262a2098ccdd2716bd8eb3 (diff)
downloadcoreboot-fcfca1da5ea4eee266c830948ec117f06a3553cd.tar.xz
Documentation: Add vboot on Lenovo devices
Describe vboot implementation details for retrofitted Lenovo ThinkPad devices. Change-Id: Ibabcc939d9d01f00a93fd42adc48057966ad877e Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com> Signed-off-by: Marcello Sylvester Bauer <sylv@sylv.io> Reviewed-on: https://review.coreboot.org/c/coreboot/+/39151 Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net> Reviewed-by: Patrick Rudolph <siro@das-labor.org> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
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-rw-r--r--Documentation/mainboard/index.md1
-rw-r--r--Documentation/mainboard/lenovo/vboot.md39
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diff --git a/Documentation/mainboard/index.md b/Documentation/mainboard/index.md
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--- a/Documentation/mainboard/index.md
+++ b/Documentation/mainboard/index.md
@@ -74,6 +74,7 @@ The boards in this section are not real mainboards, but emulators.
- [R60](lenovo/r60.md)
- [T4xx common](lenovo/t4xx_series.md)
- [X2xx common](lenovo/x2xx_series.md)
+- [VBOOT](lenovo/vboot.md)
### Arrandale series
diff --git a/Documentation/mainboard/lenovo/vboot.md b/Documentation/mainboard/lenovo/vboot.md
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index 0000000000..3e4d43bd14
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+++ b/Documentation/mainboard/lenovo/vboot.md
@@ -0,0 +1,39 @@
+# Using coreboot's verified boot on Lenovo devices
+
+By default a single instance of coreboot is present in the firmware flash,
+no verification is done and the flash is not write-protected, so as to allow
+firmware updates from the OS.
+The verified boot mechanism also called [VBOOT] allows secure firmware
+updates using an A/B partitioning scheme once enabled.
+
+## Enabling VBOOT
+You can enable [VBOOT] in Kconfig's *Security* section. Besides a verified
+boot you can also enable a measured boot by setting
+`CONFIG_VBOOT_MEASURED_BOOT`. Both options need a working TPM, which is
+present on all recent Lenovo devices.
+
+## Updating and recovery
+As the A/B partition is writeable you can still update them from the OS.
+By using the [VBOOT] mechanism you store a copy of coreboot in the `RO`
+partition that acts as failsafe in case the regular firmware update, that
+goes to the `A` or `B` partition fails.
+
+**Note:** The `RO` partition isn't write-protected by default. There's a patch
+pending on gerrit [CB:32705] that write-protects the `RO` partition.
+
+On *Lenovo* devices you can enable the *Fn* key as recovery mode switch, by
+enabling `CONFIG_H8_FN_KEY_AS_VBOOT_RECOVERY_SW`.
+Holding the *Fn* at boot will then switch to the recovery image, allowing
+to boot and flash a working image to the A/B partition.
+
+## 8 MiB ROM limitation
+*Lenovo* devices with 8 MiB ROM only have a `RO`+`A` partition enabled in the
+default FMAP. They are missing the `B` partition, due to size constaints.
+You can still provide your own FMAP if you need `RO`+`A`+`B` partitions.
+
+## CMOS
+[VBOOT] on *Lenovo* devices uses the CMOS to store configuration data, like
+boot failures and the last successfully booted partition.
+
+[VBOOT]: ../../security/vboot/index.md
+[CB:32705]: https://review.coreboot.org/32705