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We currently only describe the process to enable measured boot using bootm. Describe the UEFI requirements as well which predate bootm. Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
58 lines
2.2 KiB
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58 lines
2.2 KiB
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.. SPDX-License-Identifier: GPL-2.0+
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Measured Boot
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=============
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U-Boot can perform a measured boot, the process of hashing various components
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of the boot process, extending the results in the TPM and logging the
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component's measurement in memory for the operating system to consume.
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The functionality is available when booting via the EFI subsystem or 'bootm'
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command.
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UEFI measured boot
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------------------
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The EFI subsystem implements the `EFI TCG protocol
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<https://trustedcomputinggroup.org/resource/tcg-efi-protocol-specification/>`_
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and the `TCG PC Client Specific Platform Firmware Profile Specification
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<https://trustedcomputinggroup.org/resource/pc-client-specific-platform-firmware-profile-specification/>`_
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which defines the binaries to be measured and the corresponding PCRs to be used.
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Requirements
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~~~~~~~~~~~~
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* A hardware TPM 2.0 supported by an enabled U-Boot driver
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* CONFIG_EFI_TCG2_PROTOCOL=y
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* CONFIG_EFI_TCG2_PROTOCOL_EVENTLOG_SIZE=y
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* optional CONFIG_EFI_TCG2_PROTOCOL_MEASURE_DTB=y will measure the loaded DTB
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in PCR 1
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Legacy measured boot
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--------------------
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The commands booti, bootm, and bootz can be used for measured boot
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using the legacy entry point of the Linux kernel.
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By default, U-Boot will measure the operating system (linux) image, the
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initrd image, and the "bootargs" environment variable. By enabling
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CONFIG_MEASURE_DEVICETREE, U-Boot will also measure the devicetree image in PCR1.
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The operating system typically would verify that the hashes found in the
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TPM PCRs match the contents of the event log. This can further be checked
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against the hash results of previous boots.
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Requirements
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~~~~~~~~~~~~
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* A hardware TPM 2.0 supported by an enabled U-Boot driver
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* CONFIG_TPMv2=y
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* CONFIG_MEASURED_BOOT=y
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* Device-tree configuration of the TPM device to specify the memory area
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for event logging. The TPM device node must either contain a phandle to
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a reserved memory region or "linux,sml-base" and "linux,sml-size"
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indicating the address and size of the memory region. An example can be
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found in arch/sandbox/dts/test.dts
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* The operating system must also be configured to use the memory regions
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specified in the U-Boot device-tree in order to make use of the event
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log.
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