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0b8f35c6a5
This creates a new vboot_firmware subdirectory, and which contains the entirety of the BIOS code. There shouldn't be anything in this directory that is NOT required by the BIOS. Review URL: http://codereview.chromium.org/2219004
125 lines
4.2 KiB
Plaintext
125 lines
4.2 KiB
Plaintext
This directory contains a reference implementation for Chrome OS
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verified boot in firmware.
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Directory Structure
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The source is organized into distinct modules -
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vboot_firmware/ - Contains ONLY the code required by the BIOS to validate
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the secure boot components. There shouldn't be any code in here that signs
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or generates images. BIOS should require ONLY this directory to implement
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secure boot. Refer to vboot_firmware/README for futher details.
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cgptlib/ - Work in progress for handling GPT headers. Parts of this will no
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doubt be migrated into vboot_firmware/
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misclibs/ - Miscellaneous functions used by userland utilities.
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utility/ - Utilities for generating and verifying signed
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firmware and kernel images, as well as arbitrary blobs.
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vfirmware/ and vkernel/ - Functions for generating, verifying, and
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manipulating signed firmware and kernel images.
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tests/ - User-land tests and benchmarks that test the reference
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implementation. Please have a look at these if you'd like to
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understand how to use the reference implementation.
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Some useful utilities:
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firmware_utility.c To generate verified boot firmware images.
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kernel_utility.c To generate verified boot kernel images.
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dumpRSAPublicKey.c Dump RSA Public key (from a DER-encoded X509
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certificate) in a format suitable for
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use by RSAVerify* functions in
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crypto/.
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verify_data.c Verify a given signature on a given file.
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Generating a signed firmware image:
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* Step 1: Generate RSA root and signing keys.
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# Root key is always 8192 bits.
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$ openssl genrsa -F4 -out root_key.pem 8192
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# Signing key can be between 1024-8192 bits.
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$ openssl genrsa -F4 -out signing_key.pem <1024|2048|4096|8192>
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Note: The -F4 option must be specified to generate RSA keys with
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a public exponent of 65535. RSA keys with 3 as a public
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exponent (the default) won't work.
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* Step 2: Generate pre-processed public versions of the above keys using
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utility/dumpRSAPublicKey
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# dumpRSAPublicKey expects an x509 certificate as input.
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$ openssl req -batch -new -x509 -key root_key.pem -out root_key.crt
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$ openssl req -batch -new -x509 -key signing_key.pem -out signing_key.crt
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$ utility/dumpRSAPublicKey root_key.crt > root_key.keyb
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$ utility/dumpRSAPublicKey signing_key.crt > signing_key.keyb
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At this point we have all the requisite keys needed to generate a signed
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firmware image.
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.pem RSA Public/Private Key Pair
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.crt X509 Key Certificate
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.keyb Pre-processed RSA Public Key
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* Step 3: Use utility/firmware_utility to generate a signed firmare blob.
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$ utility/firmware_utility --generate \
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--root_key root_key.pem \
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--firmware_sign_key signing_key.pem \
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--firmware_sign_key_pub signing_key.keyb \
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--firmware_sign_algorithm <algoid> \
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--firmware_key_version 1 \
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--firmware_version 1 \
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--in <firmware blob file> \
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--out <output file>
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Where <algoid> is based on the signature algorithm to use for firmware
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signining. The list of <algoid> specifications can be output by running
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'utility/firmware_utility' without any arguments.
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Note: --firmware_key_version and --firmware_version are part of a signed
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image and are used to prevent rollbacks to older version. For testing,
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they can just be set valid values.
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* Step 4: Verify that this image verifies.
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$ utility/firmware_utility --verify \
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--in <signed firmware image>
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--root_key_pub root_key.keyb
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Verification SUCCESS.
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Note: The verification functions expects a pointer to the
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pre-processed public root key as input. For testing purposes,
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root_key.keyb can be stored in RW part of the firmware. For the
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final firmware, this will be a fixed public key which cannot be
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changed and must be stored in RO firmware.
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Generating a signed kernel image:
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The steps for generating a signed kernel image are similar to that of
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a firmware image. Since verification is chained - RO firmware verifies
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RW firmware which verifies the kernel, only the keys change. An additional
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kernel signing key must be generated. The firmware signing generated above
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is the root key equivalent for signed kernel images.
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