39 lines
1.7 KiB
Markdown
39 lines
1.7 KiB
Markdown
# 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, therefore you
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have to enable the protection in the security Kconfig menu by yourself.
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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 constraints.
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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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