6:58 a.m.
It is possible to build OVMF for SEV with an embedded Grub that can
fetch LUKS disk secrets. This adds support for injecting secrets in
the required format.
Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com>
---
docs/manpages/virt-qemu-sev-validate.rst | 83 ++++++++++
tools/virt-qemu-sev-validate | 183 +++++++++++++++++++++--
2 files changed, 257 insertions(+), 9 deletions(-)
diff --git a/docs/manpages/virt-qemu-sev-validate.rst
b/docs/manpages/virt-qemu-sev-validate.rst
index e1e290f125..db1b43a775 100644
--- a/docs/manpages/virt-qemu-sev-validate.rst
+++ b/docs/manpages/virt-qemu-sev-validate.rst
@@ -189,6 +189,46 @@ understand any configuration mistakes that have been made. If the
will be skipped. The result is that the validation will likely be reported as
failed.
+Secret injection options
+------------------------
+
+These options provide a way to inject a secret if validation of the
+launch measurement passes.
+
+``--inject-secret ALIAS-OR-GUID:PATH``
+
+Path to a file containing a secret to inject into the guest OS. Typical
+usage would be to supply a password for unlocking the root filesystem
+full disk encryption. ``ALIAS`` can be one of the well known secrets:
+
+* ``luks-key`` - bytes to use as a key for unlocking a LUKS key slot.
+ GUID of ``736869e5-84f0-4973-92ec-06879ce3da0b``.
+
+Alternatively ``GUID`` refers to an arbitrary UUID of the callers
+choosing. The contents of ``PATH`` are defined by the requirements
+of the associated GUID, and will used as-is without modification.
+In particular be aware:
+
+ * Avoid unwanted trailing newline characters in ``PATH`` unless
+ mandated by the ``GUID``.
+ * Any trailing ``NUL`` byte must be explicitly included in ``PATH``
+ if mandated by the ``GUID``.
+
+This argument can be repeated multiple times, provided a different
+``GUID`` is given for each instance.
+
+``--secret-header PATH``
+
+Path to a file in which the injected secret header will be written in base64
+format and later injected into the domain. This is required if there is no
+connection to libvirt, otherwise the secret will be directly injected.
+
+``--secret-payload PATH``
+
+Path to a file in which the injected secret payload will be written in base64
+format and later injected into the domain. This is required if there is no
+connection to libvirt, otherwise the secret will be directly injected.
+
EXAMPLES
========
@@ -263,6 +303,26 @@ automatically constructed VMSA:
--build-id 13 \
--policy 7
+Validate the measurement of a SEV guest booting from disk and
+inject a disk password on success:
+
+::
+
+ # virt-dom-sev-validate \
+ --loader OVMF.sev.fd \
+ --tk this-guest-tk.bin \
+ --measurement Zs2pf19ubFSafpZ2WKkwquXvACx9Wt/BV+eJwQ/taO8jhyIj/F8swFrybR1fZ2ID \
+ --api-major 0 \
+ --api-minor 24 \
+ --build-id 13 \
+ --policy 3 \
+ --disk-password passwd.txt \
+ --secret-header secret-header.b64 \
+ --secret-payload secret-payload.b64
+
+The ``secret-header.b64`` and ``secret-payload.b64`` files can now be sent to
+the virtualization host for injection.
+
Fetch from remote libvirt
-------------------------
@@ -323,6 +383,18 @@ automatically constructed VMSA:
--tk this-guest-tk.bin \
--domain fedora34x86_64
+Validate the measurement of a SEV guest booting from disk and
+inject a disk password on success:
+
+::
+
+ # virt-dom-sev-validate \
+ --connect qemu+ssh://root@some.remote.host/system \
+ --loader OVMF.sev.fd \
+ --tk this-guest-tk.bin \
+ --domain fedora34x86_64 \
+ --disk-password passwd.txt
+
Fetch from local libvirt
------------------------
@@ -373,6 +445,17 @@ automatically constructed VMSA:
--tk this-guest-tk.bin \
--domain fedora34x86_64
+Validate the measurement of a SEV guest booting from disk and
+inject a disk password on success:
+
+::
+
+ # virt-dom-sev-validate \
+ --insecure \
+ --tk this-guest-tk.bin \
+ --domain fedora34x86_64 \
+ --disk-password passwd.txt
+
EXIT STATUS
===========
diff --git a/tools/virt-qemu-sev-validate b/tools/virt-qemu-sev-validate
index 9eb9d54258..ac1e4c8d66 100755
--- a/tools/virt-qemu-sev-validate
+++ b/tools/virt-qemu-sev-validate
@@ -36,16 +36,19 @@
import abc
import argparse
-from base64 import b64decode
+from base64 import b64decode, b64encode
from hashlib import sha256
import hmac
import logging
+import os
import re
import socket
from struct import pack
import sys
import traceback
from uuid import UUID
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+
from lxml import etree
import libvirt
@@ -574,7 +577,46 @@ class KernelTable(GUIDTable):
return entries
-class ConfidentialVM(object):
+class SecretsTable(GUIDTable):
+
+ TABLE_GUID = UUID('{1e74f542-71dd-4d66-963e-ef4287ff173b}').bytes_le
+
+ GUID_ALIASES = {
+ "luks-key": UUID('{736869e5-84f0-4973-92ec-06879ce3da0b}')
+ }
+
+ def __init__(self):
+ super().__init__(guid=self.TABLE_GUID,
+ lenlen=4)
+ self.secrets = {}
+
+ def load_secret(self, alias_or_guid, path):
+ guid = None
+ if
re.match(r"^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$",
+ alias_or_guid):
+ guid = UUID(alias_or_guid)
+ else:
+ if alias_or_guid not in self.GUID_ALIASES:
+ raise UnsupportedUsageException(
+ "Secret alias '%s' is not known" % alias_or_guid)
+
+ guid = self.GUID_ALIASES[alias_or_guid]
+
+ if guid in self.secrets:
+ raise UnsupportedUsageException(
+ "Secret for GUID %s already loaded" % guid)
+
+ with open(path, 'rb') as fh:
+ self.secrets[guid] = fh.read()
+
+ def entries(self):
+ entries = bytes([])
+ for guid, value in self.secrets.items():
+ entries += self.build_entry(guid.bytes_le, value, 4)
+ return entries
+
+
+class ConfidentialVM(abc.ABC):
POLICY_BIT_SEV_ES = 2
POLICY_VAL_SEV_ES = (1 << POLICY_BIT_SEV_ES)
@@ -600,6 +642,7 @@ class ConfidentialVM(object):
self.vmsa_cpu1 = None
self.kernel_table = KernelTable()
+ self.secrets_table = SecretsTable()
def is_sev_es(self):
return self.policy & self.POLICY_VAL_SEV_ES
@@ -752,6 +795,82 @@ class ConfidentialVM(object):
raise AttestationFailedException(
"Measurement does not match, VM is not trustworthy")
+ def build_secrets(self):
+ measurement, _ = self.get_measurements()
+
+ iv = os.urandom(16)
+
+ secret_table = self.secrets_table.build()
+
+ cipher = Cipher(algorithms.AES(self.tek), modes.CTR(iv))
+ enc = cipher.encryptor()
+ secret_table_ciphertext = (enc.update(secret_table) +
+ enc.finalize())
+
+ flags = 0
+
+ ##
+ # Table 55. LAUNCH_SECRET Packet Header Buffer
+ ##
+ header = (
+ flags.to_bytes(4, byteorder='little') +
+ iv
+ )
+
+ # AMD Secure Encrypted Virtualization API , section 6.6
+ #
+ # hdrmac = HMAC(0x01 || FLAGS || IV || GUEST_LENGTH ||
+ # TRANS_LENGTH || DATA ||
+ # MEASURE; GCTX.TIK)
+ #
+ msg = (
+ bytes([0x01]) +
+ flags.to_bytes(4, byteorder='little') +
+ iv +
+ len(secret_table).to_bytes(4, byteorder='little') +
+ len(secret_table).to_bytes(4, byteorder='little') +
+ secret_table_ciphertext +
+ measurement
+ )
+
+ h = hmac.new(self.tik, msg, 'sha256')
+ header = (
+ flags.to_bytes(4, byteorder='little') +
+ iv +
+ h.digest()
+ )
+
+ header64 = b64encode(header).decode('utf8')
+ secret64 = b64encode(secret_table_ciphertext).decode('utf8')
+ log.debug("Header: %s (%d bytes)", header64, len(header))
+ log.debug("Secret: %s (%d bytes)",
+ secret64, len(secret_table_ciphertext))
+
+ return header64, secret64
+
+ @abc.abstractmethod
+ def inject_secrets(self):
+ pass
+
+
+class OfflineConfidentialVM(ConfidentialVM):
+ def __init__(self,
+ secret_header=None,
+ secret_payload=None,
+ **kwargs):
+ super().__init__(**kwargs)
+
+ self.secret_header = secret_header
+ self.secret_payload = secret_payload
+
+ def inject_secrets(self):
+ header64, secret64 = self.build_secrets()
+
+ with open(self.secret_header, "wb") as fh:
+ fh.write(header64.encode('utf8'))
+ with open(self.secret_payload, "wb") as fh:
+ fh.write(secret64.encode('utf8'))
+
class LibvirtConfidentialVM(ConfidentialVM):
def __init__(self, **kwargs):
@@ -939,6 +1058,14 @@ class LibvirtConfidentialVM(ConfidentialVM):
cpu_stepping = int(sig[0].get("stepping"))
self.build_vmsas(cpu_family, cpu_model, cpu_stepping)
+ def inject_secrets(self):
+ header64, secret64 = self.build_secrets()
+
+ params = {"sev-secret": secret64,
+ "sev-secret-header": header64}
+ self.dom.setLaunchSecurityState(params, 0)
+ self.dom.resume()
+
def parse_command_line():
parser = argparse.ArgumentParser(
@@ -1001,6 +1128,15 @@ def parse_command_line():
vmconn.add_argument('--ignore-config', '-g',
action='store_true',
help='Do not attempt to sanity check the guest config')
+ # Arguments related to secret injection
+ inject = parser.add_argument_group("Secret injection parameters")
+ inject.add_argument('--inject-secret', '-s', action='append',
default=[],
+ help='ALIAS-OR-GUID:PATH file containing secret to
inject')
+ inject.add_argument('--secret-payload',
+ help='Path to file to write secret data payload to')
+ inject.add_argument('--secret-header',
+ help='Path to file to write secret data header to')
+
return parser.parse_args()
@@ -1041,6 +1177,15 @@ def check_usage(args):
raise UnsupportedUsageException(
"Either --firmware or --domain is required")
+ if len(args.inject_secret) > 0:
+ if args.secret_header is None:
+ raise UnsupportedUsageException(
+ "Either --secret-header or --domain is required")
+
+ if args.secret_payload is None:
+ raise UnsupportedUsageException(
+ "Either --secret-payload or --domain is required")
+
if args.kernel is None:
if args.initrd is not None or args.cmdline is not None:
raise UnsupportedUsageException(
@@ -1060,15 +1205,22 @@ def check_usage(args):
raise UnsupportedUsageException(
"CPU SKU needs family, model and stepping for SEV-ES domain")
+ secret = [args.secret_payload, args.secret_header]
+ if secret.count(None) > 0 and secret.count(None) != len(secret):
+ raise UnsupportedUsageException(
+ "Both --secret-payload and --secret-header are required")
+
def attest(args):
if args.domain is None:
- cvm = ConfidentialVM(measurement=args.measurement,
- api_major=args.api_major,
- api_minor=args.api_minor,
- build_id=args.build_id,
- policy=args.policy,
- num_cpus=args.num_cpus)
+ cvm = OfflineConfidentialVM(measurement=args.measurement,
+ api_major=args.api_major,
+ api_minor=args.api_minor,
+ build_id=args.build_id,
+ policy=args.policy,
+ num_cpus=args.num_cpus,
+ secret_header=args.secret_header,
+ secret_payload=args.secret_payload)
else:
cvm = LibvirtConfidentialVM(measurement=args.measurement,
api_major=args.api_major,
@@ -1112,10 +1264,23 @@ def attest(args):
args.ignore_config)
cvm.attest()
-
if not args.quiet:
print("OK: Looks good to me")
+ for secret in args.inject_secret:
+ bits = secret.split(":")
+ if len(bits) != 2:
+ raise UnsupportedUsageException(
+ "Expecting ALIAS-OR-GUID:PATH for injected secret")
+
+ cvm.secrets_table.load_secret(bits[0], bits[1])
+
+ if len(args.inject_secret) > 0:
+ cvm.inject_secrets()
+ if not args.quiet:
+ print("OK: Injected %d secrets" % len(args.inject_secret))
+
+
def main():
args = parse_command_line()
if args.debug:
--
2.37.3