stub(tpm): Measure "UKI" (i.e. all unified sections in our stub)

rust/stub/Cargo.lock

@@ -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"

rust/stub/Cargo.toml

@@ -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"

rust/stub/src/main.rs

@@ -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");

rust/stub/src/measure.rs

@@ -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)
+}

rust/stub/src/pe_section.rs

@@ -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.

rust/stub/src/tpm.rs

@@ -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)
+}

rust/stub/src/unified_sections.rs

@@ -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)
+    }
+}