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Merge pull request #167 from nix-community/sd-stub-tpm2 

feat: minimal poc for TPM measurements à la sd-stub
This commit is contained in:
Ryan Lahfa 2023-05-18 19:16:30 +02:00 committed by GitHub
parent 354ec6f451 f603e0c134
commit 3a5e15f4ac
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8 changed files with 399 additions and 50 deletions
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142
nix/tests/lanzaboote.nix
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@ -3,10 +3,90 @@
}:
let
inherit (pkgs) lib;
inherit (pkgs) lib system;
mkSecureBootTest = { name, machine ? { }, useSecureBoot ? true, useTPM2 ? false, readEfiVariables ? false, testScript }:
let
tpmSocketPath = "/tmp/swtpm-sock";
tpmDeviceModels = {
x86_64-linux = "tpm-tis";
aarch64-linux = "tpm-tis-device";
};
# Should go to nixpkgs.
efiVariablesHelpers = ''
import struct
SD_LOADER_GUID = "4a67b082-0a4c-41cf-b6c7-440b29bb8c4f"
def read_raw_variable(var: str) -> bytes:
attr_var = machine.succeed(f"cat /sys/firmware/efi/efivars/{var}-{SD_LOADER_GUID}").encode('raw_unicode_escape')
_ = attr_var[:4] # First 4 bytes are attributes according to https://www.kernel.org/doc/html/latest/filesystems/efivarfs.html
value = attr_var[4:]
return value
def read_string_variable(var: str, encoding='utf-16-le') -> str:
return read_raw_variable(var).decode(encoding).rstrip('\x00')
# By default, it will read a 4 byte value, read `struct` docs to change the format.
def assert_variable_uint(var: str, expected: int, format: str = 'I'):
with subtest(f"Is `{var}` set to {expected} (uint)"):
value, = struct.unpack(f'<{format}', read_raw_variable(var))
assert value == expected, f"Unexpected variable value in `{var}`, expected: `{expected}`, actual: `{value}`"
def assert_variable_string(var: str, expected: str, encoding='utf-16-le'):
with subtest(f"Is `{var}` correctly set"):
value = read_string_variable(var, encoding)
assert value == expected, f"Unexpected variable value in `{var}`, expected: `{expected.encode(encoding)!r}`, actual: `{value.encode(encoding)!r}`"
def assert_variable_string_contains(var: str, expected_substring: str):
with subtest(f"Do `{var}` contain expected substrings"):
value = read_string_variable(var).strip()
assert expected_substring in value, f"Did not find expected substring in `{var}`, expected substring: `{expected_substring}`, actual value: `{value}`"
'';
tpm2Initialization = ''
import subprocess
from tempfile import TemporaryDirectory
# From systemd-initrd-luks-tpm2.nix
class Tpm:
def __init__(self):
self.state_dir = TemporaryDirectory()
self.start()
def start(self):
self.proc = subprocess.Popen(["${pkgs.swtpm}/bin/swtpm",
"socket",
"--tpmstate", f"dir={self.state_dir.name}",
"--ctrl", "type=unixio,path=${tpmSocketPath}",
"--tpm2",
])
# Check whether starting swtpm failed
try:
exit_code = self.proc.wait(timeout=0.2)
if exit_code is not None and exit_code != 0:
raise Exception("failed to start swtpm")
except subprocess.TimeoutExpired:
pass
"""Check whether the swtpm process exited due to an error"""
def check(self):
exit_code = self.proc.poll()
if exit_code is not None and exit_code != 0:
raise Exception("swtpm process died")
tpm = Tpm()
@polling_condition
def swtpm_running():
tpm.check()
'';
in
pkgs.nixosTest {
inherit name;
testScript = ''
${lib.optionalString useTPM2 tpm2Initialization}
${lib.optionalString readEfiVariables efiVariablesHelpers}
${testScript}
'';
mkSecureBootTest = { name, machine ? { }, useSecureBoot ? true, testScript }: pkgs.nixosTest {
inherit name testScript;
nodes.machine = { lib, ... }: {
imports = [
lanzabooteModule
@ -17,9 +97,23 @@ let
useBootLoader = true;
useEFIBoot = true;
efi.OVMF = pkgs.OVMF.override {
secureBoot = useSecureBoot;
tpmSupport = useTPM2; # This is needed otherwise OVMF won't initialize the TPM2 protocol.
};
qemu.options = lib.mkIf useTPM2 [
"-chardev socket,id=chrtpm,path=${tpmSocketPath}"
"-tpmdev emulator,id=tpm_dev_0,chardev=chrtpm"
"-device ${tpmDeviceModels.${system}},tpmdev=tpm_dev_0"
];
inherit useSecureBoot;
};
boot.initrd.availableKernelModules = lib.mkIf useTPM2 [ "tpm_tis" ];
boot.loader.efi = {
canTouchEfiVariables = true;
};
@ -271,9 +365,8 @@ in
export-efi-variables = mkSecureBootTest {
name = "lanzaboote-exports-efi-variables";
machine.environment.systemPackages = [ pkgs.efibootmgr ];
readEfiVariables = true;
testScript = ''
import struct
# We will choose to boot directly on the stub.
# To perform this trick, we will boot first with systemd-boot.
# Then, we will add a new boot entry in EFI with higher priority
@ -301,7 +394,6 @@ in
"test -e /sys/firmware/efi/efivars/LoaderEntrySelected-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f && false || true"
)
SD_LOADER_GUID = "4a67b082-0a4c-41cf-b6c7-440b29bb8c4f"
expected_variables = ["LoaderDevicePartUUID",
"LoaderImageIdentifier",
"LoaderFirmwareInfo",
@ -310,20 +402,6 @@ in
"StubFeatures"
]
def read_raw_variable(var: str) -> bytes:
attr_var = machine.succeed(f"cat /sys/firmware/efi/efivars/{var}-{SD_LOADER_GUID}").encode('raw_unicode_escape')
return attr_var[4:] # First 4 bytes are attributes according to https://www.kernel.org/doc/html/latest/filesystems/efivarfs.html
def read_string_variable(var: str, encoding='utf-16-le') -> str:
return read_raw_variable(var).decode(encoding).rstrip('\x00')
def assert_variable_string(var: str, expected: str, encoding='utf-16-le'):
with subtest(f"Is `{var}` correctly set"):
value = read_string_variable(var, encoding)
assert value == expected, f"Unexpected variable value in `{var}`, expected: `{expected.encode(encoding)!r}`, actual: `{value.encode(encoding)!r}`"
def assert_variable_string_contains(var: str, expected_substring: str):
with subtest(f"Do `{var}` contain expected substrings"):
value = read_string_variable(var).strip()
assert expected_substring in value, f"Did not find expected substring in `{var}`, expected substring: `{expected_substring}`, actual value: `{value}`"
# Debug all systemd loader specification GUID EFI variables loaded by the current environment.
print(machine.succeed(f"ls /sys/firmware/efi/efivars/*-{SD_LOADER_GUID}"))
with subtest("Check if supported variables are exported"):
@ -344,4 +422,28 @@ in
assert struct.unpack('<Q', read_raw_variable("StubFeatures")) != 0
'';
};
tpm2-export-efi-variables = mkSecureBootTest {
name = "lanzaboote-tpm2-exports-efi-variables";
useTPM2 = true;
readEfiVariables = true;
testScript = ''
machine.start()
# TODO: the other variables are not yet supported.
expected_variables = [
"StubPcrKernelImage"
]
# Debug all systemd loader specification GUID EFI variables loaded by the current environment.
print(machine.succeed(f"ls /sys/firmware/efi/efivars/*-{SD_LOADER_GUID}"))
with subtest("Check if supported variables are exported"):
for expected_var in expected_variables:
machine.succeed(f"test -e /sys/firmware/efi/efivars/{expected_var}-{SD_LOADER_GUID}")
# "Static" parts of the UKI is measured in PCR11
assert_variable_uint("StubPcrKernelImage", 11)
'';
};
}

7
rust/stub/Cargo.lock generated
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@ -92,6 +92,7 @@ dependencies = [
"bitflags 2.2.1",
"goblin",
"log",
"sha1_smol",
"sha2",
"uefi",
"uefi-services",
@ -176,6 +177,12 @@ dependencies = [
"syn",
]
[[package]]
name = "sha1_smol"
version = "1.0.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "ae1a47186c03a32177042e55dbc5fd5aee900b8e0069a8d70fba96a9375cd012"
[[package]]
name = "sha2"
version = "0.10.6"

2
rust/stub/Cargo.toml
View File

@ -17,6 +17,8 @@ log = { version = "0.4.17", default-features = false, features = [ "max_level_in
# Use software implementation because the UEFI target seems to need it.
sha2 = { version = "0.10.6", default-features = false, features = ["force-soft"] }
# SHA1 for TPM TCG interface version 1.
sha1_smol = "1.0.0"
[profile.release]
opt-level = "s"

25
rust/stub/src/main.rs
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@ -6,16 +6,21 @@ extern crate alloc;
mod efivars;
mod linux_loader;
mod measure;
mod pe_loader;
mod pe_section;
mod tpm;
mod uefi_helpers;
mod unified_sections;
use alloc::vec::Vec;
use efivars::{export_efi_variables, get_loader_features, EfiLoaderFeatures};
use log::{debug, info, warn};
use log::{info, warn};
use measure::measure_image;
use pe_loader::Image;
use pe_section::{pe_section, pe_section_as_string};
use sha2::{Digest, Sha256};
use tpm::tpm_available;
use uefi::{
prelude::*,
proto::{
@ -238,10 +243,26 @@ fn main(handle: Handle, mut system_table: SystemTable<Boot>) -> Status {
warn!("Hash mismatch for initrd!");
}
if tpm_available(system_table.boot_services()) {
info!("TPM available, will proceed to measurements.");
unsafe {
// Iterate over unified sections and measure them
// For now, ignore failures during measurements.
// TODO: in the future, devise a threat model where this can fail
// and ensure this hard-fail correctly.
let _ = measure_image(
&system_table,
booted_image_file(system_table.boot_services()).unwrap(),
);
// TODO: Measure kernel parameters
// TODO: Measure sysexts
}
}
if let Ok(features) = get_loader_features(system_table.runtime_services()) {
if !features.contains(EfiLoaderFeatures::RandomSeed) {
// FIXME: process random seed then on the disk.
debug!("Random seed is available, but lanzaboote does not support it yet.");
info!("Random seed is available, but lanzaboote does not support it yet.");
}
}
export_efi_variables(&system_table).expect("Failed to export stub EFI variables");

65
rust/stub/src/measure.rs Normal file
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@ -0,0 +1,65 @@
use log::info;
use uefi::{
cstr16,
proto::tcg::PcrIndex,
table::{runtime::VariableAttributes, Boot, SystemTable},
};
use crate::{
efivars::BOOT_LOADER_VENDOR_UUID, pe_section::pe_section_data, tpm::tpm_log_event_ascii,
uefi_helpers::PeInMemory, unified_sections::UnifiedSection,
};
const TPM_PCR_INDEX_KERNEL_IMAGE: PcrIndex = PcrIndex(11);
pub unsafe fn measure_image(
system_table: &SystemTable<Boot>,
image: PeInMemory,
) -> uefi::Result<u32> {
let runtime_services = system_table.runtime_services();
let boot_services = system_table.boot_services();
// SAFETY: We get a slice that represents our currently running
// image and then parse the PE data structures from it. This is
// safe, because we don't touch any data in the data sections that
// might conceivably change while we look at the slice.
// (data sections := all unified sections that can be measured.)
let pe_binary = unsafe { image.as_slice() };
let pe = goblin::pe::PE::parse(pe_binary).map_err(|_err| uefi::Status::LOAD_ERROR)?;
let mut measurements = 0;
for section in pe.sections {
let section_name = section.name().map_err(|_err| uefi::Status::UNSUPPORTED)?;
if let Ok(unified_section) = UnifiedSection::try_from(section_name) {
// UNSTABLE: && in the previous if is an unstable feature
// https://github.com/rust-lang/rust/issues/53667
if unified_section.should_be_measured() {
// Here, perform the TPM log event in ASCII.
if let Some(data) = pe_section_data(pe_binary, &section) {
info!("Measuring section `{}`...", section_name);
if tpm_log_event_ascii(
boot_services,
TPM_PCR_INDEX_KERNEL_IMAGE,
data,
section_name,
)? {
measurements += 1;
}
}
}
}
}
if measurements > 0 {
// If we did some measurements, expose a variable encoding the PCR where
// we have done the measurements.
runtime_services.set_variable(
cstr16!("StubPcrKernelImage"),
&BOOT_LOADER_VENDOR_UUID,
VariableAttributes::BOOTSERVICE_ACCESS | VariableAttributes::RUNTIME_ACCESS,
&TPM_PCR_INDEX_KERNEL_IMAGE.0.to_le_bytes(),
)?;
}
Ok(measurements)
}

24
rust/stub/src/pe_section.rs
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@ -5,8 +5,21 @@
#![allow(clippy::bind_instead_of_map)]
use alloc::{borrow::ToOwned, string::String};
use goblin::pe::section_table::SectionTable;
/// Extracts the data of a section of a loaded PE file.
/// Extracts the data of a section in a loaded PE file
/// based on the section table.
pub fn pe_section_data<'a>(pe_data: &'a [u8], section: &SectionTable) -> Option<&'a [u8]> {
let section_start: usize = section.virtual_address.try_into().ok()?;
assert!(section.virtual_size <= section.size_of_raw_data);
let section_end: usize = section_start + usize::try_from(section.virtual_size).ok()?;
Some(&pe_data[section_start..section_end])
}
/// Extracts the data of a section of a loaded PE file
/// based on the section name.
pub fn pe_section<'a>(pe_data: &'a [u8], section_name: &str) -> Option<&'a [u8]> {
let pe_binary = goblin::pe::PE::parse(pe_data).ok()?;
@ -14,14 +27,7 @@ pub fn pe_section<'a>(pe_data: &'a [u8], section_name: &str) -> Option<&'a [u8]>
.sections
.iter()
.find(|s| s.name().map(|n| n == section_name).unwrap_or(false))
.and_then(|s| {
let section_start: usize = s.virtual_address.try_into().ok()?;
assert!(s.virtual_size <= s.size_of_raw_data);
let section_end: usize = section_start + usize::try_from(s.virtual_size).ok()?;
Some(&pe_data[section_start..section_end])
})
.and_then(|s| pe_section_data(pe_data, s))
}
/// Extracts the data of a section of a loaded PE image and returns it as a string.

106
rust/stub/src/tpm.rs Normal file
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@ -0,0 +1,106 @@
use alloc::vec;
use core::mem::{self, MaybeUninit};
use log::warn;
use uefi::{
prelude::BootServices,
proto::tcg::{
v1::{self, Sha1Digest},
v2, EventType, PcrIndex,
},
table::boot::ScopedProtocol,
};
fn open_capable_tpm2(boot_services: &BootServices) -> uefi::Result<ScopedProtocol<v2::Tcg>> {
let tpm_handle = boot_services.get_handle_for_protocol::<v2::Tcg>()?;
let mut tpm_protocol = boot_services.open_protocol_exclusive::<v2::Tcg>(tpm_handle)?;
let capabilities = tpm_protocol.get_capability()?;
/*
* Here's systemd-stub perform a cast to EFI_TCG_BOOT_SERVICE_CAPABILITY
* indicating there could be some quirks to workaround.
* It should probably go to uefi-rs?
if capabilities.structure_version.major == 1 && capabilities.structure_version.minor == 0 {
}*/
if !capabilities.tpm_present() {
warn!("Capability `TPM present` is not there for the existing TPM TCGv2 protocol");
return Err(uefi::Status::UNSUPPORTED.into());
}
Ok(tpm_protocol)
}
fn open_capable_tpm1(boot_services: &BootServices) -> uefi::Result<ScopedProtocol<v1::Tcg>> {
let tpm_handle = boot_services.get_handle_for_protocol::<v1::Tcg>()?;
let mut tpm_protocol = boot_services.open_protocol_exclusive::<v1::Tcg>(tpm_handle)?;
let status_check = tpm_protocol.status_check()?;
if status_check.protocol_capability.tpm_deactivated()
|| !status_check.protocol_capability.tpm_present()
{
warn!("Capability `TPM present` is not there or `TPM deactivated` is there for the existing TPM TCGv1 protocol");
return Err(uefi::Status::UNSUPPORTED.into());
}
Ok(tpm_protocol)
}
pub fn tpm_available(boot_services: &BootServices) -> bool {
open_capable_tpm2(boot_services).is_ok() || open_capable_tpm1(boot_services).is_ok()
}
/// Log an event in the TPM with `buffer` as data.
/// Returns a boolean whether the measurement has been done or not in case of success.
pub fn tpm_log_event_ascii(
boot_services: &BootServices,
pcr_index: PcrIndex,
buffer: &[u8],
description: &str,
) -> uefi::Result<bool> {
if pcr_index.0 == u32::MAX {
return Ok(false);
}
if let Ok(mut tpm2) = open_capable_tpm2(boot_services) {
let required_size = mem::size_of::<u32>()
// EventHeader is private…
+ mem::size_of::<u32>() + mem::size_of::<u16>() + mem::size_of::<PcrIndex>() + mem::size_of::<EventType>()
+ description.len();
let mut event_buffer = vec![MaybeUninit::<u8>::uninit(); required_size];
let event = v2::PcrEventInputs::new_in_buffer(
event_buffer.as_mut_slice(),
pcr_index,
EventType::IPL,
description.as_bytes(),
)?;
// FIXME: what do we want as flags here?
tpm2.hash_log_extend_event(Default::default(), buffer, event)?;
} else if let Ok(mut tpm1) = open_capable_tpm1(boot_services) {
let required_size = mem::size_of::<PcrIndex>()
+ mem::size_of::<EventType>()
+ mem::size_of::<Sha1Digest>()
+ mem::size_of::<u32>()
+ description.len();
let mut event_buffer = vec![MaybeUninit::<u8>::uninit(); required_size];
// Compute sha1 of the event data
let mut m = sha1_smol::Sha1::new();
m.update(description.as_bytes());
let event = v1::PcrEvent::new_in_buffer(
event_buffer.as_mut_slice(),
pcr_index,
EventType::IPL,
m.digest().bytes(),
description.as_bytes(),
)?;
tpm1.hash_log_extend_event(event, Some(buffer))?;
}
Ok(true)
}

40
rust/stub/src/unified_sections.rs Normal file
View File

@ -0,0 +1,40 @@
/// List of PE sections that have a special meaning with respect to
/// UKI specification.
/// This is the canonical order in which they are measured into TPM
/// PCR 11.
/// !!! DO NOT REORDER !!!
#[repr(u8)]
pub enum UnifiedSection {
Linux = 0,
OsRel = 1,
CmdLine = 2,
Initrd = 3,
Splash = 4,
Dtb = 5,
PcrSig = 6,
PcrPkey = 7,
}
impl TryFrom<&str> for UnifiedSection {
type Error = uefi::Error;
fn try_from(value: &str) -> Result<Self, Self::Error> {
Ok(match value {
".linux" => Self::Linux,
".osrel" => Self::OsRel,
".cmdline" => Self::CmdLine,
".initrd" => Self::Initrd,
".splash" => Self::Splash,
".dtb" => Self::Dtb,
".pcrsig" => Self::PcrSig,
".pcrpkey" => Self::PcrPkey,
_ => return Err(uefi::Status::INVALID_PARAMETER.into()),
})
}
}
impl UnifiedSection {
/// Whether this section should be measured into TPM.
pub fn should_be_measured(&self) -> bool {
!matches!(self, UnifiedSection::PcrSig)
}
}