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libvirt/tools/virt-qemu-sev-validate
Jim Fehlig 0f350a4d07 tools: Fix detection of remote libvirt access in virt-qemu-sev-validate 
The VM's firmware path is not extracted from the XML when invoking
virt-qemu-sev-validate in insecure mode and connecting to the local libvirt

virt-qemu-sev-validate --insecure --tk tek-tik.bin --domain test-sev-es
ERROR: Cannot access firmware path remotely

The test for remote access compares the return value from socket.gethostname()
to the return value from conn.getHostname(). The former doesn't always return
the fqdn, whereas the latter does. Use socket.getfqdn() instead.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
2023-02-03 11:28:56 -07:00

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#!/usr/bin/env python3
#
# SPDX-License-Identifier: LGPL-2.1-or-later
#
# Validates a guest AMD SEV launch measurement
#
# A general principle in writing this tool is that it must calculate the
# expected measurement based entirely on information it receives on the CLI
# from the guest owner.
#
# It cannot generally trust information obtained from the guest XML or from the
# virtualization host OS. The main exceptions are:
#
# - The guest measurement
#
# This is a result of cryptographic operation using a shared secret known
# only to the guest owner and SEV platform, not the host OS.
#
# - The guest policy
#
# This is encoded in the launch session blob that is encrypted with a shared
# secret known only to the guest owner and SEV platform, not the host OS. It
# is impossible for the host OS to maliciously launch a guest with different
# policy and the user provided launch session blob.
#
# CAVEAT: the user must ALWAYS create a launch blob with freshly generated
# TIK/TEK for every new VM. Re-use of the same TIK/TEK for multiple VMs
# is insecure.
#
# - The SEV API version / build ID
#
# This does not have an impact on the security of the measurement, unless
# the guest owner needs a guarantee that the host is not using specific
# firmware versions with known flaws.
#
import abc
import argparse
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
log = logging.getLogger()
class AttestationFailedException(Exception):
pass
class UnsupportedUsageException(Exception):
pass
class InsecureUsageException(Exception):
pass
class IncorrectConfigException(Exception):
pass
class InvalidStateException(Exception):
pass
class Field(object):
U8 = 0
U16 = 2
U32 = 4
U64 = 8
SCALAR = 0
BITMASK = 1
ARRAY = 2
def __init__(self, name, size, fmt, value, order):
self.name = name
self.size = size
self.value = value
self.fmt = fmt
self.order = order
class Struct(object):
def __init__(self, size):
self._fields = {}
self.size = size
def register_field(self, name, size, fmt=Field.SCALAR, defvalue=0):
self._fields[name] = Field(name, size, fmt,
defvalue, len(self.fields))
@property
def fields(self):
return sorted(self._fields.values(), key=lambda f: f.order)
def __getattr__(self, name):
return self._fields[name]
def __setattr__(self, name, value):
if name in ["_fields", "size"]:
super().__setattr__(name, value)
else:
self._fields[name].value = value
def binary_format(self):
fmt = ["<"]
datalen = 0
for field in self.fields:
if field.size == Field.U8:
if field.fmt == Field.ARRAY:
datalen += len(field.value)
fmt += ["%dB" % len(field.value)]
else:
datalen += 1
fmt += ["B"]
elif field.size == Field.U16:
datalen += 2
fmt += ["H"]
elif field.size == Field.U32:
datalen += 4
fmt += ["L"]
elif field.size == Field.U64:
datalen += 8
fmt += ["Q"]
pad = self.size - datalen
assert self.size >= 1
fmt += ["%dB" % pad]
return "".join(fmt), pad
def pack(self):
fmt, pad = self.binary_format()
values = []
for field in self.fields:
if field.size == Field.U8 and field.fmt == Field.ARRAY:
for _, k in enumerate(field.value):
values.append(k)
else:
values.append(field.value)
values.extend([0] * pad)
return pack(fmt, *values)
class VMSA(Struct):
ATTR_G_SHIFT = 23
ATTR_G_MASK = (1 << ATTR_G_SHIFT)
ATTR_B_SHIFT = 22
ATTR_B_MASK = (1 << ATTR_B_SHIFT)
ATTR_L_SHIFT = 21
ATTR_L_MASK = (1 << ATTR_L_SHIFT)
ATTR_AVL_SHIFT = 20
ATTR_AVL_MASK = (1 << ATTR_AVL_SHIFT)
ATTR_P_SHIFT = 15
ATTR_P_MASK = (1 << ATTR_P_SHIFT)
ATTR_DPL_SHIFT = 13
ATTR_DPL_MASK = (3 << ATTR_DPL_SHIFT)
ATTR_S_SHIFT = 12
ATTR_S_MASK = (1 << ATTR_S_SHIFT)
ATTR_TYPE_SHIFT = 8
ATTR_TYPE_MASK = (15 << ATTR_TYPE_SHIFT)
ATTR_A_MASK = (1 << 8)
ATTR_CS_MASK = (1 << 11)
ATTR_C_MASK = (1 << 10)
ATTR_R_MASK = (1 << 9)
ATTR_E_MASK = (1 << 10)
ATTR_W_MASK = (1 << 9)
def __init__(self):
super().__init__(4096)
# From Linux arch/x86/include/asm/svm.h, we're unpacking the
# struct vmcb_save_area
self.register_field("es_selector", Field.U16)
self.register_field("es_attrib", Field.U16, Field.BITMASK)
self.register_field("es_limit", Field.U32)
self.register_field("es_base", Field.U64)
self.register_field("cs_selector", Field.U16)
self.register_field("cs_attrib", Field.U16, Field.BITMASK)
self.register_field("cs_limit", Field.U32)
self.register_field("cs_base", Field.U64)
self.register_field("ss_selector", Field.U16)
self.register_field("ss_attrib", Field.U16, Field.BITMASK)
self.register_field("ss_limit", Field.U32)
self.register_field("ss_base", Field.U64)
self.register_field("ds_selector", Field.U16)
self.register_field("ds_attrib", Field.U16, Field.BITMASK)
self.register_field("ds_limit", Field.U32)
self.register_field("ds_base", Field.U64)
self.register_field("fs_selector", Field.U16)
self.register_field("fs_attrib", Field.U16, Field.BITMASK)
self.register_field("fs_limit", Field.U32)
self.register_field("fs_base", Field.U64)
self.register_field("gs_selector", Field.U16)
self.register_field("gs_attrib", Field.U16, Field.BITMASK)
self.register_field("gs_limit", Field.U32)
self.register_field("gs_base", Field.U64)
self.register_field("gdtr_selector", Field.U16)
self.register_field("gdtr_attrib", Field.U16, Field.BITMASK)
self.register_field("gdtr_limit", Field.U32)
self.register_field("gdtr_base", Field.U64)
self.register_field("ldtr_selector", Field.U16)
self.register_field("ldtr_attrib", Field.U16, Field.BITMASK)
self.register_field("ldtr_limit", Field.U32)
self.register_field("ldtr_base", Field.U64)
self.register_field("idtr_selector", Field.U16)
self.register_field("idtr_attrib", Field.U16, Field.BITMASK)
self.register_field("idtr_limit", Field.U32)
self.register_field("idtr_base", Field.U64)
self.register_field("tr_selector", Field.U16)
self.register_field("tr_attrib", Field.U16, Field.BITMASK)
self.register_field("tr_limit", Field.U32)
self.register_field("tr_base", Field.U64)
self.register_field("reserved_1",
Field.U8, Field.ARRAY, bytearray([0] * 43))
self.register_field("cpl", Field.U8)
self.register_field("reserved_2",
Field.U8, Field.ARRAY, bytearray([0] * 4))
self.register_field("efer", Field.U64)
self.register_field("reserved_3",
Field.U8, Field.ARRAY, bytearray([0] * 104))
self.register_field("xss", Field.U64)
self.register_field("cr4", Field.U64)
self.register_field("cr3", Field.U64)
self.register_field("cr0", Field.U64)
self.register_field("dr7", Field.U64)
self.register_field("dr6", Field.U64)
self.register_field("rflags", Field.U64)
self.register_field("rip", Field.U64)
self.register_field("reserved_4",
Field.U8, Field.ARRAY, bytearray([0] * 88))
self.register_field("rsp", Field.U64)
self.register_field("reserved_5",
Field.U8, Field.ARRAY, bytearray([0] * 24))
self.register_field("rax", Field.U64)
self.register_field("star", Field.U64)
self.register_field("lstar", Field.U64)
self.register_field("cstar", Field.U64)
self.register_field("sfmask", Field.U64)
self.register_field("kernel_gs_base", Field.U64)
self.register_field("sysenter_cs", Field.U64)
self.register_field("sysenter_esp", Field.U64)
self.register_field("sysenter_eip", Field.U64)
self.register_field("cr2", Field.U64)
self.register_field("reserved_6",
Field.U8, Field.ARRAY, bytearray([0] * 32))
self.register_field("g_pat", Field.U64)
self.register_field("dbgctl", Field.U64)
self.register_field("br_from", Field.U64)
self.register_field("br_to", Field.U64)
self.register_field("last_excp_from", Field.U64)
self.register_field("last_excp_to", Field.U64)
self.register_field("reserved_7",
Field.U8, Field.ARRAY, bytearray([0] * 72))
self.register_field("spec_ctrl", Field.U32)
self.register_field("reserved_7b",
Field.U8, Field.ARRAY, bytearray([0] * 4))
self.register_field("pkru", Field.U32)
self.register_field("reserved_7a",
Field.U8, Field.ARRAY, bytearray([0] * 20))
self.register_field("reserved_8", Field.U64) # rax duplicate
self.register_field("rcx", Field.U64)
self.register_field("rdx", Field.U64, Field.BITMASK)
self.register_field("rbx", Field.U64)
self.register_field("reserved_9", Field.U64) # rsp duplicate
self.register_field("rbp", Field.U64)
self.register_field("rsi", Field.U64)
self.register_field("rdi", Field.U64)
self.register_field("r8", Field.U64)
self.register_field("r9", Field.U64)
self.register_field("r10", Field.U64)
self.register_field("r11", Field.U64)
self.register_field("r12", Field.U64)
self.register_field("r13", Field.U64)
self.register_field("r14", Field.U64)
self.register_field("r15", Field.U64)
self.register_field("reserved_10",
Field.U8, Field.ARRAY, bytearray([0] * 16))
self.register_field("sw_exit_code", Field.U64)
self.register_field("sw_exit_info_1", Field.U64)
self.register_field("sw_exit_info_2", Field.U64)
self.register_field("sw_scratch", Field.U64)
self.register_field("reserved_11",
Field.U8, Field.ARRAY, bytearray([0] * 56))
self.register_field("xcr0", Field.U64)
self.register_field("valid_bitmap",
Field.U8, Field.ARRAY, bytearray([0] * 16))
self.register_field("x87_state_gpa",
Field.U64)
def amd64_cpu_init(self):
# AMD64 Architecture Programmer’s Manual
# Volume 2: System Programming.
#
# 14.1.3 Processor Initialization State
#
# Values after INIT
self.cr0 = (1 << 4)
self.rip = 0xfff0
self.cs_selector = 0xf000
self.cs_base = 0xffff0000
self.cs_limit = 0xffff
self.ds_limit = 0xffff
self.es_limit = 0xffff
self.fs_limit = 0xffff
self.gs_limit = 0xffff
self.ss_limit = 0xffff
self.gdtr_limit = 0xffff
self.idtr_limit = 0xffff
self.ldtr_limit = 0xffff
self.tr_limit = 0xffff
self.dr6 = 0xffff0ff0
self.dr7 = 0x0400
self.rflags = 0x2
self.xcr0 = 0x1
def kvm_cpu_init(self):
# svm_set_cr4() sets guest X86_CR4_MCE bit if host
# has X86_CR4_MCE enabled
self.cr4 = 0x40
# svm_set_efer sets guest EFER_SVME (Secure Virtual Machine enable)
self.efer = 0x1000
# init_vmcb + init_sys_seg() sets
# SVM_SELECTOR_P_MASK | SEG_TYPE_LDT
self.ldtr_attrib = 0x0082
# init_vmcb + init_sys_seg() sets
# SVM_SELECTOR_P_MASK | SEG_TYPE_BUSY_TSS16
self.tr_attrib = 0x0083
# kvm_arch_vcpu_create() in arch/x86/kvm/x86.c
self.g_pat = 0x0007040600070406
def qemu_cpu_init(self):
# Based on logic in x86_cpu_reset()
#
# file target/i386/cpu.c
def attr(mask):
return (mask >> VMSA.ATTR_TYPE_SHIFT)
self.ldtr_attrib = attr(VMSA.ATTR_P_MASK |
(2 << VMSA.ATTR_TYPE_SHIFT))
self.tr_attrib = attr(VMSA.ATTR_P_MASK |
(11 << VMSA.ATTR_TYPE_SHIFT))
self.cs_attrib = attr(VMSA.ATTR_P_MASK |
VMSA.ATTR_S_MASK |
VMSA.ATTR_CS_MASK |
VMSA.ATTR_R_MASK |
VMSA.ATTR_A_MASK)
self.ds_attrib = attr(VMSA.ATTR_P_MASK |
VMSA.ATTR_S_MASK |
VMSA.ATTR_W_MASK |
VMSA.ATTR_A_MASK)
self.es_attrib = attr(VMSA.ATTR_P_MASK |
VMSA.ATTR_S_MASK |
VMSA.ATTR_W_MASK |
VMSA.ATTR_A_MASK)
self.ss_attrib = attr(VMSA.ATTR_P_MASK |
VMSA.ATTR_S_MASK |
VMSA.ATTR_W_MASK |
VMSA.ATTR_A_MASK)
self.fs_attrib = attr(VMSA.ATTR_P_MASK |
VMSA.ATTR_S_MASK |
VMSA.ATTR_W_MASK |
VMSA.ATTR_A_MASK)
self.gs_attrib = attr(VMSA.ATTR_P_MASK |
VMSA.ATTR_S_MASK |
VMSA.ATTR_W_MASK |
VMSA.ATTR_A_MASK)
self.g_pat = 0x0007040600070406
def cpu_sku(self, family, model, stepping):
stepping &= 0xf
model &= 0xff
family &= 0xfff
self.rdx.value = stepping
if family > 0xf:
self.rdx.value |= 0xf00 | ((family - 0x0f) << 20)
else:
self.rdx.value |= family << 8
self.rdx.value |= ((model & 0xf) << 4) | ((model >> 4) << 16)
def reset_addr(self, reset_addr):
reset_cs = reset_addr & 0xffff0000
reset_ip = reset_addr & 0x0000ffff
self.rip.value = reset_ip
self.cs_base.value = reset_cs
class OVMF(object):
OVMF_TABLE_FOOTER_GUID = UUID("96b582de-1fb2-45f7-baea-a366c55a082d")
SEV_INFO_BLOCK_GUID = UUID("00f771de-1a7e-4fcb-890e-68c77e2fb44e")
def __init__(self):
self.entries = {}
def load(self, content):
expect = OVMF.OVMF_TABLE_FOOTER_GUID.bytes_le
actual = content[-48:-32]
if expect != actual:
raise Exception("OVMF footer GUID not found")
tablelen = int.from_bytes(content[-50:-48], byteorder='little')
if tablelen == 0:
raise Exception("OVMF tables zero length")
table = content[-(32 + tablelen):-50]
self.parse_table(table)
def parse_table(self, data):
while len(data) > 0:
entryuuid = UUID(bytes_le=data[-16:])
entrylen = int.from_bytes(data[-18:-16], byteorder='little')
entrydata = data[-entrylen:-18]
self.entries[str(entryuuid)] = entrydata
data = data[0:-entrylen]
def reset_addr(self):
if str(OVMF.SEV_INFO_BLOCK_GUID) not in self.entries:
raise Exception("SEV info block GUID not found")
reset_addr = int.from_bytes(
self.entries[str(OVMF.SEV_INFO_BLOCK_GUID)], "little")
return reset_addr
class GUIDTable(abc.ABC):
GUID_LEN = 16
def __init__(self, guid, lenlen=2):
self.guid = guid
self.lenlen = lenlen
@abc.abstractmethod
def entries(self):
pass
def build_entry(self, guid, payload, lenlen):
dummylen = int(0).to_bytes(lenlen, 'little')
entry = bytearray(guid + dummylen + payload)
lenle = len(entry).to_bytes(lenlen, 'little')
entry[self.GUID_LEN:(self.GUID_LEN + lenlen)] = lenle
return bytes(entry)
def build(self):
payload = self.entries()
if len(payload) == 0:
return bytes([])
dummylen = int(0).to_bytes(self.lenlen, 'little')
table = bytearray(self.guid + dummylen + payload)
guidlen = len(table).to_bytes(self.lenlen, 'little')
table[self.GUID_LEN:(self.GUID_LEN + self.lenlen)] = guidlen
pad = 16 - (len(table) % 16)
table += bytes([0]) * pad
log.debug("Table(hex): %s", bytes(table).hex())
return bytes(table)
class KernelTable(GUIDTable):
TABLE_GUID = UUID('{9438d606-4f22-4cc9-b479-a793-d411fd21}').bytes_le
KERNEL_GUID = UUID('{4de79437-abd2-427f-b835-d5b1-72d2045b}').bytes_le
INITRD_GUID = UUID('{44baf731-3a2f-4bd7-9af1-41e2-9169781d}').bytes_le
CMDLINE_GUID = UUID('{97d02dd8-bd20-4c94-aa78-e771-4d36ab2a}').bytes_le
def __init__(self):
super().__init__(guid=self.TABLE_GUID,
lenlen=2)
self.kernel = None
self.initrd = None
self.cmdline = None
def load_kernel(self, path):
with open(path, "rb") as fh:
self.kernel = sha256(fh.read()).digest()
def load_initrd(self, path):
with open(path, "rb") as fh:
self.initrd = sha256(fh.read()).digest()
def load_cmdline(self, val):
self.cmdline = sha256(val.encode("utf8") + bytes([0])).digest()
def entries(self):
entries = bytes([])
if self.kernel is None:
return entries
if self.initrd is None:
self.initrd = sha256(bytes([])).digest()
if self.cmdline is None:
self.cmdline = sha256(bytes([0])).digest()
log.debug("Kernel(sha256): %s", self.kernel.hex())
log.debug("Initrd(sha256): %s", self.initrd.hex())
log.debug("Cmdline(sha256): %s", self.cmdline.hex())
entries += self.build_entry(self.CMDLINE_GUID, self.cmdline, 2)
entries += self.build_entry(self.INITRD_GUID, self.initrd, 2)
entries += self.build_entry(self.KERNEL_GUID, self.kernel, 2)
return entries
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)
def __init__(self,
measurement=None,
api_major=None,
api_minor=None,
build_id=None,
policy=None,
num_cpus=None):
self.measurement = measurement
self.api_major = api_major
self.api_minor = api_minor
self.build_id = build_id
self.policy = policy
self.firmware = None
self.tik = None
self.tek = None
self.num_cpus = num_cpus
self.vmsa_cpu0 = None
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
def load_tik_tek(self, tik_path, tek_path):
with open(tik_path, 'rb') as fh:
self.tik = fh.read()
log.debug("TIK(hex): %s", self.tik.hex())
if len(self.tik) != 16:
raise UnsupportedUsageException(
"Expected 16 bytes in TIK file, but got %d" % len(self.tik))
with open(tek_path, 'rb') as fh:
self.tek = fh.read()
log.debug("TEK(hex): %s", self.tek.hex())
if len(self.tek) != 16:
raise UnsupportedUsageException(
"Expected 16 bytes in TEK file, but got %d" % len(self.tek))
def load_tk(self, tk_path):
with open(tk_path, 'rb') as fh:
tk = fh.read()
if len(tk) != 32:
raise UnsupportedUsageException(
"Expected 32 bytes in TIK/TEK file, but got %d" % len(tk))
self.tek = tk[0:16]
self.tik = tk[16:32]
log.debug("TIK(hex): %s", self.tik.hex())
log.debug("TEK(hex): %s", self.tek.hex())
def load_firmware(self, firmware_path):
with open(firmware_path, 'rb') as fh:
self.firmware = fh.read()
log.debug("Firmware(sha256): %s", sha256(self.firmware).hexdigest())
@staticmethod
def _load_vmsa(path):
with open(path, 'rb') as fh:
vmsa = fh.read()
if len(vmsa) != 4096:
raise UnsupportedUsageException(
"VMSA must be 4096 bytes in length")
return vmsa
def load_vmsa_cpu0(self, path):
self.vmsa_cpu0 = self._load_vmsa(path)
log.debug("VMSA CPU 0(sha256): %s",
sha256(self.vmsa_cpu0).hexdigest())
def load_vmsa_cpu1(self, path):
self.vmsa_cpu1 = self._load_vmsa(path)
log.debug("VMSA CPU 1(sha256): %s",
sha256(self.vmsa_cpu1).hexdigest())
def build_vmsas(self, family, model, stepping):
ovmf = OVMF()
ovmf.load(self.firmware)
vmsa = VMSA()
vmsa.amd64_cpu_init()
vmsa.kvm_cpu_init()
vmsa.qemu_cpu_init()
vmsa.cpu_sku(family, model, stepping)
self.vmsa_cpu0 = vmsa.pack()
log.debug("VMSA CPU 0(sha256): %s",
sha256(self.vmsa_cpu0).hexdigest())
vmsa.reset_addr(ovmf.reset_addr())
self.vmsa_cpu1 = vmsa.pack()
log.debug("VMSA CPU 1(sha256): %s",
sha256(self.vmsa_cpu1).hexdigest())
def get_cpu_state(self):
if self.num_cpus is None:
raise UnsupportedUsageException(
"Number of virtual CPUs must be specified for SEV-ES domain")
if self.vmsa_cpu0 is None:
raise UnsupportedUsageException(
"VMSA for boot CPU required for SEV-ES domain")
if self.num_cpus > 1 and self.vmsa_cpu1 is None:
raise UnsupportedUsageException(
"VMSA for additional CPUs required for SEV-ES domain with SMP")
vmsa = self.vmsa_cpu0 + (self.vmsa_cpu1 * (self.num_cpus - 1))
log.debug("VMSA(sha256): %s", sha256(vmsa).hexdigest())
return vmsa
# Get the full set of measured launch data for the domain
#
# The measured data that the guest is initialized with is the concatenation
# of the following:
#
# - The firmware blob
# - The kernel GUID table
def get_measured_data(self):
measured_data = (self.firmware +
self.kernel_table.build())
if self.is_sev_es():
measured_data += self.get_cpu_state()
log.debug("Measured-data(sha256): %s",
sha256(measured_data).hexdigest())
return measured_data
# Get the reported and computed launch measurements for the domain
#
# AMD Secure Encrypted Virtualization API , section 6.5:
#
# measurement = HMAC(0x04 || API_MAJOR || API_MINOR || BUILD ||
# GCTX.POLICY || GCTX.LD || MNONCE; GCTX.TIK)
#
# Where GCTX.LD covers all the measured data the guest is initialized with
# per get_measured_data().
def get_measurements(self):
measurement = b64decode(self.measurement)
reported = measurement[0:32]
nonce = measurement[32:48]
measured_data = self.get_measured_data()
msg = (
bytes([0x4]) +
self.api_major.to_bytes(1, 'little') +
self.api_minor.to_bytes(1, 'little') +
self.build_id.to_bytes(1, 'little') +
self.policy.to_bytes(4, 'little') +
sha256(measured_data).digest() +
nonce
)
log.debug("Measured-msg(hex): %s", msg.hex())
computed = hmac.new(self.tik, msg, 'sha256').digest()
log.debug("Measurement reported(hex): %s", reported.hex())
log.debug("Measurement computed(hex): %s", computed.hex())
return reported, computed
def attest(self):
reported, computed = self.get_measurements()
if reported != computed:
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):
super().__init__(**kwargs)
self.conn = None
self.dom = None
def check_domain(self, doc, secure):
ls = doc.xpath("/domain/launchSecurity[@type='sev']")
if len(ls) != 1:
raise IncorrectConfigException(
"Domain is not configured with SEV launch security")
dh = doc.xpath("/domain/launchSecurity[@type='sev']/dhCert")
if len(dh) != 1:
raise IncorrectConfigException(
"Domain must have SEV owner cert to validate measurement")
session = doc.xpath("/domain/launchSecurity[@type='sev']/session")
if len(session) != 1:
raise IncorrectConfigException(
"Domain must have SEV session data to validate measurement")
nvramnodes = doc.xpath("/domain/os/nvram")
if len(nvramnodes) != 0 and secure:
raise InsecureUsageException(
"Domain firmware with NVRAM cannot be securely measured")
loadernodes = doc.xpath("/domain/os/loader")
if len(loadernodes) != 1:
raise IncorrectConfigException(
"Domain must have one firmware path")
measure_kernel_nodes = doc.xpath(
"/domain/launchSecurity[@type='sev']/@kernelHashes")
measure_kernel = False
if len(measure_kernel_nodes) == 1:
if measure_kernel_nodes[0] == "yes":
measure_kernel = True
xp_kernel = "/domain/os/kernel"
xp_initrd = "/domain/os/initrd"
xp_cmdline = "/domain/os/cmdline"
kern_nodes = (doc.xpath(xp_kernel) +
doc.xpath(xp_initrd) +
doc.xpath(xp_cmdline))
if not measure_kernel:
if len(self.kernel_table.entries()) != 0:
raise UnsupportedUsageException(
"kernel/initrd/cmdline provided but kernel "
"measurement not enabled")
# Check for an insecure scenario
if len(kern_nodes) != 0 and secure:
raise InsecureUsageException(
"direct kernel boot present without measurement")
else:
if len(kern_nodes) == 0:
raise IncorrectConfigException(
"kernel/initrd/cmdline not provided but kernel "
"measurement is enabled")
def load_domain(self, uri, id_name_uuid, secure, ignore_config):
self.conn = libvirt.open(uri)
remote = socket.getfqdn() != self.conn.getHostname()
if not remote and secure:
raise InsecureUsageException(
"running locally on the hypervisor host is not secure")
if re.match(r'^\d+$', id_name_uuid):
self.dom = self.conn.lookupByID(int(id_name_uuid))
elif re.match(r'^[-a-f0-9]+$', id_name_uuid):
self.dom = self.conn.lookupByUUIDString(id_name_uuid)
else:
self.dom = self.conn.lookupByName(id_name_uuid)
log.debug("VM: id=%d name=%s uuid=%s",
self.dom.ID(), self.dom.name(), self.dom.UUIDString())
if not self.dom.isActive():
raise InvalidStateException(
"Domain must be running to validate measurement")
state = self.dom.info()[0]
if state != libvirt.VIR_DOMAIN_PAUSED and secure:
raise InvalidStateException(
"Domain must be paused to validate measurement")
xml = self.dom.XMLDesc()
doc = etree.fromstring(xml)
if not ignore_config:
self.check_domain(doc, secure)
# See comments at top of file wrt why we are OK to trust the
# sev-api-major, sev-api-minor, sev-build-id and sev-policy data
# reported by the host
sevinfo = self.dom.launchSecurityInfo()
if "sev-api-major" not in sevinfo:
raise UnsupportedUsageException(
"'api-major' not reported in domain launch security info")
if self.measurement is None:
self.measurement = sevinfo["sev-measurement"]
if self.api_major is None:
self.api_major = sevinfo["sev-api-major"]
if self.api_minor is None:
self.api_minor = sevinfo["sev-api-minor"]
if self.build_id is None:
self.build_id = sevinfo["sev-build-id"]
if self.policy is None:
self.policy = sevinfo["sev-policy"]
if self.is_sev_es() and self.num_cpus is None:
if secure:
raise InsecureUsageException(
"Using CPU count from guest is not secure")
info = self.dom.info()
self.num_cpus = info[3]
if self.firmware is None:
if remote:
raise UnsupportedUsageException(
"Cannot access firmware path remotely")
if secure:
raise InsecureUsageException(
"Using firmware path from XML is not secure")
loadernodes = doc.xpath("/domain/os/loader")
if len(loadernodes) == 0:
raise UnsupportedUsageException(
"--firmware not specified and no firmware path found")
self.load_firmware(loadernodes[0].text)
if self.kernel_table.kernel is None:
kernelnodes = doc.xpath("/domain/os/kernel")
if len(kernelnodes) != 0:
if remote:
raise UnsupportedUsageException(
"Cannot access kernel path remotely")
if secure:
raise InsecureUsageException(
"Using kernel path from XML is not secure")
self.kernel_table.load_kernel(kernelnodes[0].text)
if self.kernel_table.initrd is None:
initrdnodes = doc.xpath("/domain/os/initrd")
if len(initrdnodes) != 0:
if remote:
raise UnsupportedUsageException(
"Cannot access initrd path remotely")
if secure:
raise InsecureUsageException(
"Using initrd path from XML is not secure")
self.kernel_table.load_initrd(initrdnodes[0].text)
if self.kernel_table.cmdline is None:
cmdlinenodes = doc.xpath("/domain/os/cmdline")
if len(cmdlinenodes) != 0:
if secure:
raise InsecureUsageException(
"Using cmdline string from XML is not secure")
self.kernel_table.load_cmdline(cmdlinenodes[0].text)
capsxml = self.conn.getCapabilities()
capsdoc = etree.fromstring(capsxml)
if self.is_sev_es() and self.vmsa_cpu0 is None:
if secure:
raise InsecureUsageException(
"Using CPU SKU from capabilities is not secure")
sig = capsdoc.xpath("/capabilities/host/cpu/signature")
if len(sig) != 1:
raise UnsupportedUsageException(
"Libvirt is too old to report host CPU signature")
cpu_family = int(sig[0].get("family"))
cpu_model = int(sig[0].get("model"))
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(
description='Validate guest AMD SEV launch measurement')
parser.add_argument('--debug', '-d', action='store_true',
help='Show debug information')
parser.add_argument('--quiet', '-q', action='store_true',
help='Do not display status')
# Arguments related to the state of the launched guest
vmstate = parser.add_argument_group("Virtual machine launch state")
vmstate.add_argument('--measurement', '-m',
help='Measurement for the running domain')
vmstate.add_argument('--api-major', type=int,
help='SEV API major version for the running domain')
vmstate.add_argument('--api-minor', type=int,
help='SEV API minor version for the running domain')
vmstate.add_argument('--build-id', type=int,
help='SEV build ID for the running domain')
vmstate.add_argument('--policy', type=int,
help='SEV policy for the running domain')
# Arguments related to calculation of the expected launch measurement
vmconfig = parser.add_argument_group("Virtual machine config")
vmconfig.add_argument('--firmware', '-f',
help='Path to the firmware binary')
vmconfig.add_argument('--kernel', '-k',
help='Path to the kernel binary')
vmconfig.add_argument('--initrd', '-r',
help='Path to the initrd binary')
vmconfig.add_argument('--cmdline', '-e',
help='Cmdline string booted with')
vmconfig.add_argument('--num-cpus', '-n', type=int,
help='Number of virtual CPUs')
vmconfig.add_argument('--vmsa-cpu0', '-0',
help='VMSA state for the boot CPU')
vmconfig.add_argument('--vmsa-cpu1', '-1',
help='VMSA state for the additional CPUs')
vmconfig.add_argument('--cpu-family', type=int,
help='Hypervisor host CPU family number')
vmconfig.add_argument('--cpu-model', type=int,
help='Hypervisor host CPU model number')
vmconfig.add_argument('--cpu-stepping', type=int,
help='Hypervisor host CPU stepping number')
vmconfig.add_argument('--tik',
help='TIK file for domain')
vmconfig.add_argument('--tek',
help='TEK file for domain')
vmconfig.add_argument('--tk',
help='TEK/TIK combined file for domain')
# Arguments related to the connection to libvirt
vmconn = parser.add_argument_group("Libvirt guest connection")
vmconn.add_argument('--connect', '-c', default="qemu:///system",
help='libvirt connection URI')
vmconn.add_argument('--domain', '-o',
help='domain ID / Name / UUID')
vmconn.add_argument('--insecure', '-i', action='store_true',
help='Proceed even if usage scenario is insecure')
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()
# Sanity check the set of CLI args specified provide enough info for us to do
# the job
def check_usage(args):
if args.tk is not None:
if args.tik is not None or args.tek is not None:
raise UnsupportedUsageException(
"--tk is mutually exclusive with --tek/--tik")
else:
if args.tik is None or args.tek is None:
raise UnsupportedUsageException(
"Either --tk or both of --tek/--tik are required")
if args.domain is None:
if args.measurement is None:
raise UnsupportedUsageException(
"Either --measurement or --domain is required")
if args.api_major is None:
raise UnsupportedUsageException(
"Either --api-major or --domain is required")
if args.api_minor is None:
raise UnsupportedUsageException(
"Either --api-minor or --domain is required")
if args.build_id is None:
raise UnsupportedUsageException(
"Either --build-id or --domain is required")
if args.policy is None:
raise UnsupportedUsageException(
"Either --policy or --domain is required")
if args.firmware is None:
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(
"--initrd/--cmdline require --kernel")
sku = [args.cpu_family, args.cpu_model, args.cpu_stepping]
if sku.count(None) == len(sku):
if args.vmsa_cpu1 is not None and args.vmsa_cpu0 is None:
raise UnsupportedUsageException(
"VMSA for additional CPU also requires VMSA for boot CPU")
else:
if args.vmsa_cpu0 is not None or args.vmsa_cpu1 is not None:
raise UnsupportedUsageException(
"VMSA files are mutually exclusive with CPU SKU")
if sku.count(None) != 0:
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 = 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,
api_minor=args.api_minor,
build_id=args.build_id,
policy=args.policy,
num_cpus=args.num_cpus)
if args.firmware is not None:
cvm.load_firmware(args.firmware)
if args.tk is not None:
cvm.load_tk(args.tk)
else:
cvm.load_tik_tek(args.tik, args.tek)
if args.kernel is not None:
cvm.kernel_table.load_kernel(args.kernel)
if args.initrd is not None:
cvm.kernel_table.load_initrd(args.initrd)
if args.cmdline is not None:
cvm.kernel_table.load_cmdline(args.cmdline)
if args.vmsa_cpu0 is not None:
cvm.load_vmsa_cpu0(args.vmsa_cpu0)
if args.vmsa_cpu1 is not None:
cvm.load_vmsa_cpu1(args.vmsa_cpu1)
if args.cpu_family is not None:
cvm.build_vmsas(args.cpu_family,
args.cpu_model,
args.cpu_stepping)
if args.domain is not None:
cvm.load_domain(args.connect,
args.domain,
not args.insecure,
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:
logging.basicConfig(level="DEBUG")
formatter = logging.Formatter("[%(levelname)s]: %(message)s")
handler = log.handlers[0]
handler.setFormatter(formatter)
try:
check_usage(args)
attest(args)
sys.exit(0)
except AttestationFailedException as e:
if args.debug:
traceback.print_tb(e.__traceback__)
if not args.quiet:
print("ERROR: %s" % e, file=sys.stderr)
sys.exit(1)
except UnsupportedUsageException as e:
if args.debug:
traceback.print_tb(e.__traceback__)
if not args.quiet:
print("ERROR: %s" % e, file=sys.stderr)
sys.exit(2)
except InsecureUsageException as e:
if not args.quiet:
print("ERROR: %s" % e, file=sys.stderr)
sys.exit(3)
except IncorrectConfigException as e:
if not args.quiet:
print("ERROR: %s" % e, file=sys.stderr)
sys.exit(4)
except InvalidStateException as e:
if not args.quiet:
print("ERROR: %s" % e, file=sys.stderr)
sys.exit(5)
except Exception as e:
if args.debug:
traceback.print_tb(e.__traceback__)
if not args.quiet:
print("ERROR: %s" % e, file=sys.stderr)
sys.exit(6)
if __name__ == "__main__":
main()
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