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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@ -74,6 +74,7 @@ The boards in this section are not real mainboards, but emulators.
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- [R60](lenovo/r60.md)
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- [T4xx common](lenovo/t4xx_series.md)
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- [X2xx common](lenovo/x2xx_series.md)
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- [VBOOT](lenovo/vboot.md)
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### Arrandale series
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@ -0,0 +1,39 @@
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# Using coreboot's verified boot on Lenovo devices
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By default a single instance of coreboot is present in the firmware flash,
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no verification is done and the flash is not write-protected, so as to allow
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firmware updates from the OS.
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The verified boot mechanism also called [VBOOT] allows secure firmware
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updates using an A/B partitioning scheme once enabled.
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## Enabling VBOOT
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You can enable [VBOOT] in Kconfig's *Security* section. Besides a verified
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boot you can also enable a measured boot by setting
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`CONFIG_VBOOT_MEASURED_BOOT`. Both options need a working TPM, which is
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present on all recent Lenovo devices.
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## Updating and recovery
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As the A/B partition is writeable you can still update them from the OS.
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By using the [VBOOT] mechanism you store a copy of coreboot in the `RO`
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partition that acts as failsafe in case the regular firmware update, that
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goes to the `A` or `B` partition fails.
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**Note:** The `RO` partition isn't write-protected by default. There's a patch
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pending on gerrit [CB:32705] that write-protects the `RO` partition.
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On *Lenovo* devices you can enable the *Fn* key as recovery mode switch, by
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enabling `CONFIG_H8_FN_KEY_AS_VBOOT_RECOVERY_SW`.
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Holding the *Fn* at boot will then switch to the recovery image, allowing
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to boot and flash a working image to the A/B partition.
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## 8 MiB ROM limitation
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*Lenovo* devices with 8 MiB ROM only have a `RO`+`A` partition enabled in the
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default FMAP. They are missing the `B` partition, due to size constaints.
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You can still provide your own FMAP if you need `RO`+`A`+`B` partitions.
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## CMOS
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[VBOOT] on *Lenovo* devices uses the CMOS to store configuration data, like
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boot failures and the last successfully booted partition.
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[VBOOT]: ../../security/vboot/index.md
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[CB:32705]: https://review.coreboot.org/32705
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