qemu: enroll certificate in MOK for dm-verity and kernel mods #3018
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![github-advanced-security[bot]](https://avatars.githubusercontent.com/in/57789?s=60&v=4){kind=small}
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behrmann
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Sep 11, 2024
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DaanDeMeyer
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DaanDeMeyer
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Sep 12, 2024
mkosi/qemu.py
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| if config.secure_boot_certificate: | ||
| run( | ||
| [ | ||
| "virt-fw-vars", | ||
| "--input", vars, | ||
| "--output", ovmf_vars.name, | ||
| "--set-json", ovmf_json.name, | ||
| "--loglevel", "WARNING", | ||
| ], | ||
| sandbox=config.sandbox( | ||
| binary=qemu, | ||
| options=[ | ||
| "--bind", ovmf_vars.name, ovmf_vars.name, | ||
| "--ro-bind", ovmf_json.name, ovmf_json.name, | ||
| "--ro-bind", vars, vars, | ||
| ], | ||
| ), | ||
| ) | ||
| else: | ||
| shutil.copy2(vars, Path(ovmf_vars.name)) |
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This should be dropped, just because the image is built with a secure boot certificate shouldn't imply that we automatically add it to any given OVMF variables, especially ones provided by the user.
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it's now skipped if there are user-provided vars
DaanDeMeyer
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mkosi/qemu.py
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| # In order to make the kernel use mkosi.crt to verify dm-verity volumes, we need to | ||
| # create runtime and volatile EFI variables, MokListTrustedRT and MokListRT, as | ||
| # it's only from kernel 6.11 that db is used for this purpose. Note that, unlike | ||
| # certificates in db, the certificates in MOK are only used if secure boot is enabled. | ||
| # First create an efivar with the certificate, and then read it and convert to the | ||
| # json format that virt-fw-vars expects. | ||
| # attr=4 means EFI_VARIABLE_RUNTIME_ACCESS, and the GUID is the well-known MOK one. | ||
|
|
||
| mok_sigdb = stack.enter_context(tempfile.NamedTemporaryFile(prefix="mkosi-ovmf-vars-sigdb-")) | ||
| run( | ||
| [ | ||
| "virt-fw-sigdb", | ||
| "--add-cert", "605dab50-e046-4300-abb6-3dd810dd8b23", config.secure_boot_certificate, | ||
| "--output", mok_sigdb.name, | ||
| ], | ||
| sandbox=config.sandbox( | ||
| binary=qemu, | ||
| options=[ | ||
| "--bind", mok_sigdb.name, mok_sigdb.name, | ||
| "--ro-bind", config.secure_boot_certificate, config.secure_boot_certificate, | ||
| ], | ||
| ), | ||
| ) | ||
|
|
||
| mok_json = { | ||
| "version": 2, | ||
| "variables": [ | ||
| { | ||
| "name": "MokListRT", | ||
| "guid": "605dab50-e046-4300-abb6-3dd810dd8b23", | ||
| "attr": 4, | ||
| "data": mok_sigdb.read().hex(), | ||
| }, | ||
| { | ||
| "name": "MokListTrustedRT", | ||
| "guid": "605dab50-e046-4300-abb6-3dd810dd8b23", | ||
| "attr": 4, | ||
| "data": "01", | ||
| }, | ||
| ], | ||
| } | ||
| ovmf_json.write(json.dumps(mok_json).encode()) | ||
| ovmf_json.flush() |
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Make this a function and call it from within the custom if block and assert on secure_boot_certificate
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Automatically enroll the secure boot certificate in MOK, and also set the boolean so that the kernel trusts it to verify kernel modules and dm-verity volumes. This requires secure boot to be enabled to be effective, otherwise the kernel will ignore it.
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DaanDeMeyer
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| if (config.secure_boot_certificate and | ||
| (config.qemu_firmware_variables == Path("microsoft") or not config.qemu_firmware_variables)): |
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As mentioned in Telegram, I would really prefer we don't conditionalize based on whether there's a secure boot certificate configured or not as that's build time configuration and not runtime configuration. So if you'd like to have this for the microsoft keys as well please gate it behind a new constant for QemuFirmwareVariables= named microsoft+mok
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Automatically enroll the secure boot certificate in MOK, and also set the boolean so that the kernel trusts it to verify kernel modules and dm-verity volumes. This requires secure boot to be enabled to be effective, otherwise the kernel will ignore it.