qemu: enroll certificate in MOK for dm-verity and kernel mods

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.

mkosi/qemu.py

@@ -646,20 +646,62 @@ def finalize_firmware_variables(
     stack: contextlib.ExitStack,
 ) -> tuple[Path, str]:
     ovmf_vars = stack.enter_context(tempfile.NamedTemporaryFile(prefix="mkosi-ovmf-vars-"))
+    ovmf_json = stack.enter_context(tempfile.NamedTemporaryFile(prefix="mkosi-ovmf-vars-json-"))
+    have_mok_json = False
+
+    if config.secure_boot_certificate:
+        try:
+            from virt.firmware.efi import guids, siglist
+
+            # 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 = siglist.EfiSigDB()
+            mok_sigdb.add_cert(guids.parse_str("605dab50-e046-4300-abb6-3dd810dd8b23"), config.secure_boot_certificate)
+            mok_json = dict(
+                version=2,
+                variables=[
+                    dict(
+                        name="MokListRT",
+                        guid="605dab50-e046-4300-abb6-3dd810dd8b23",
+                        attr=4,
+                        data=bytes(mok_sigdb).hex(),
+                    ),
+                    dict(
+                        name="MokListTrustedRT",
+                        guid="605dab50-e046-4300-abb6-3dd810dd8b23",
+                        attr=4,
+                        data="01",
+                    ),
+                ],
+            )
+            ovmf_json.write(json.dumps(mok_json).encode())
+            ovmf_json.flush()
+            have_mok_json = True
+        except ImportError:
+            pass
+
     if config.qemu_firmware_variables in (None, Path("custom"), Path("microsoft")):
         ovmf_vars_format = ovmf.vars_format
     else:
         ovmf_vars_format = "raw"
 
     if config.qemu_firmware_variables == Path("custom"):
         assert config.secure_boot_certificate
+        assert have_mok_json
         run(
             [
                 "virt-fw-vars",
                 "--input", ovmf.vars,
                 "--output", ovmf_vars.name,
                 "--enroll-cert", config.secure_boot_certificate,
                 "--add-db", "OvmfEnrollDefaultKeys", config.secure_boot_certificate,
+                "--set-json", ovmf_json.name,
                 "--no-microsoft",
                 "--secure-boot",
                 "--loglevel", "WARNING",
@@ -669,6 +711,7 @@ def finalize_firmware_variables(
                 options=[
                     "--bind", ovmf_vars.name, ovmf_vars.name,
                     "--ro-bind", config.secure_boot_certificate, config.secure_boot_certificate,
+                    "--ro-bind", ovmf_json.name, ovmf_json.name,
                 ],
             ),
         )
@@ -679,7 +722,25 @@ def finalize_firmware_variables(
             if config.qemu_firmware_variables == Path("microsoft") or not config.qemu_firmware_variables
             else config.qemu_firmware_variables
         )
-        shutil.copy2(vars, Path(ovmf_vars.name))
+        if have_mok_json:
+            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,
+                    ],
+                ),
+            )
+        else:
+            shutil.copy2(vars, Path(ovmf_vars.name))
 
     return Path(ovmf_vars.name), ovmf_vars_format
 

pyproject.toml

@@ -45,6 +45,8 @@ pythonVersion = "3.9"
 
 [tool.mypy]
 python_version = 3.9
+# Fails on external libraries like virt.firmware
+ignore_missing_imports = true
 # belonging to --strict
 warn_unused_configs = true
 disallow_any_generics = true