feat(shim): initial shim support

src/actions/chainload.rs

@@ -1,5 +1,6 @@
 use crate::context::SproutContext;
 use crate::integrations::bootloader_interface::BootloaderInterface;
+use crate::integrations::shim::{ShimInput, ShimSupport};
 use crate::utils;
 use crate::utils::media_loader::MediaLoaderHandle;
 use crate::utils::media_loader::constants::linux::LINUX_EFI_INITRD_MEDIA_GUID;
@@ -40,15 +41,9 @@ pub fn chainload(context: Rc<SproutContext>, configuration: &ChainloadConfigurat
     )
     .context("unable to resolve chainload path")?;
 
-    // Load the image to chainload.
+    // Load the image to chainload using the shim support integration.
-    let image = uefi::boot::load_image(
+    // It will determine if the image needs to be loaded via the shim or can be loaded directly.
-        sprout_image,
+    let image = ShimSupport::load(sprout_image, ShimInput::ResolvedPath(&resolved))?;
-        uefi::boot::LoadImageSource::FromDevicePath {
-            device_path: &resolved.full_path,
-            boot_policy: uefi::proto::BootPolicy::ExactMatch,
-        },
-    )
-    .context("unable to load image")?;
 
     // Open the LoadedImage protocol of the image to chainload.
     let mut loaded_image_protocol = uefi::boot::open_protocol_exclusive::<LoadedImage>(image)

src/drivers.rs

@@ -1,4 +1,5 @@
 use crate::context::SproutContext;
+use crate::integrations::shim::{ShimInput, ShimSupport};
 use crate::utils;
 use anyhow::{Context, Result};
 use log::info;
@@ -6,7 +7,6 @@ use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
 use std::rc::Rc;
 use uefi::boot::SearchType;
-use uefi::proto::device_path::LoadedImageDevicePath;
 
 /// Declares a driver configuration.
 /// Drivers allow extending the functionality of Sprout.
@@ -23,28 +23,17 @@ pub struct DriverDeclaration {
 fn load_driver(context: Rc<SproutContext>, driver: &DriverDeclaration) -> Result<()> {
     // Acquire the handle and device path of the loaded image.
     let sprout_image = uefi::boot::image_handle();
-    let image_device_path_protocol =
-        uefi::boot::open_protocol_exclusive::<LoadedImageDevicePath>(sprout_image)
-            .context("unable to open loaded image device path protocol")?;
 
-    // Get the device path root of the sprout image.
+    // Resolve the path to the driver image.
-    let mut full_path = utils::device_path_root(&image_device_path_protocol)?;
+    let resolved = utils::resolve_path(
-
+        context.root().loaded_image_path()?,
-    // Push the path of the driver from the root.
+        &context.stamp(&driver.path),
-    full_path.push_str(&context.stamp(&driver.path));
-
-    // Convert the path to a device path.
-    let device_path = utils::text_to_device_path(&full_path)?;
-
-    // Load the driver image.
-    let image = uefi::boot::load_image(
-        sprout_image,
-        uefi::boot::LoadImageSource::FromDevicePath {
-            device_path: &device_path,
-            boot_policy: uefi::proto::BootPolicy::ExactMatch,
-        },
     )
-    .context("unable to load image")?;
+    .context("unable to resolve path to driver")?;
+
+    // Load the driver image using the shim support integration.
+    // It will determine if the image needs to be loaded via the shim or can be loaded directly.
+    let image = ShimSupport::load(sprout_image, ShimInput::ResolvedPath(&resolved))?;
 
     // Start the driver image, this is expected to return control to sprout.
     // There is no guarantee that the driver will actually return control as it is

src/integrations.rs

@@ -1,2 +1,4 @@
 /// Implements support for the bootloader interface specification.
 pub mod bootloader_interface;
+/// Implements support for the shim loader application for Secure Boot.
+pub mod shim;

src/integrations/shim.rs

@@ -0,0 +1,193 @@
+use crate::utils;
+use crate::utils::ResolvedPath;
+use anyhow::{Context, Result, anyhow, bail};
+use std::ffi::c_void;
+use uefi::Handle;
+use uefi::boot::LoadImageSource;
+use uefi::proto::device_path::DevicePath;
+use uefi::proto::unsafe_protocol;
+use uefi_raw::{Guid, Status, guid};
+
+/// Support for the shim loader application for Secure Boot.
+pub struct ShimSupport;
+
+/// Input to the shim mechanisms.
+pub enum ShimInput<'a> {
+    /// Data loaded into a buffer and ready to be verified, owned.
+    OwnedDataBuffer(Option<&'a ResolvedPath>, Vec<u8>),
+    /// Data loaded into a buffer and ready to be verified.
+    DataBuffer(Option<&'a ResolvedPath>, &'a [u8]),
+    /// Data is provided as a resolved path. We will need to load the data to verify it.
+    /// The output will them return the loaded data.
+    ResolvedPath(&'a ResolvedPath),
+}
+
+impl<'a> ShimInput<'a> {
+    /// Accesses the buffer behind the shim input, if available.
+    pub fn buffer(&self) -> Option<&[u8]> {
+        match self {
+            ShimInput::OwnedDataBuffer(_, data) => Some(data),
+            ShimInput::DataBuffer(_, data) => Some(data),
+            ShimInput::ResolvedPath(_) => None,
+        }
+    }
+
+    /// Accesses the full device path to the input.
+    pub fn file_path(&self) -> Option<&DevicePath> {
+        match self {
+            ShimInput::OwnedDataBuffer(path, _) => path.as_ref().map(|it| it.full_path.as_ref()),
+            ShimInput::DataBuffer(path, _) => path.as_ref().map(|it| it.full_path.as_ref()),
+            ShimInput::ResolvedPath(path) => Some(path.full_path.as_ref()),
+        }
+    }
+
+    /// Converts this input into an owned data buffer, where the data is loaded.
+    /// For ResolvedPath, this will read the file.
+    pub fn into_owned_data_buffer(self) -> Result<ShimInput<'a>> {
+        match self {
+            ShimInput::OwnedDataBuffer(root, data) => Ok(ShimInput::OwnedDataBuffer(root, data)),
+
+            ShimInput::DataBuffer(root, data) => {
+                Ok(ShimInput::OwnedDataBuffer(root, data.to_vec()))
+            }
+
+            ShimInput::ResolvedPath(path) => {
+                Ok(ShimInput::OwnedDataBuffer(Some(path), path.read_file()?))
+            }
+        }
+    }
+}
+
+/// Output of the shim verification function.
+/// Since the shim needs to load the data from disk, we will optimize by using that as the data
+/// to actually boot.
+pub enum ShimVerificationOutput {
+    /// The verification failed.
+    VerificationFailed,
+    /// The data provided to the verifier was already a buffer.
+    VerifiedDataNotLoaded,
+    /// Verifying the data resulted in loading the data from the source.
+    /// This contains the data that was loaded, so it won't need to be loaded again.
+    VerifiedDataBuffer(Vec<u8>),
+}
+
+/// The shim lock protocol as defined by the shim loader application.
+#[unsafe_protocol(ShimSupport::SHIM_LOCK_GUID)]
+struct ShimLockProtocol {
+    /// Verify the data in `buffer` with the size `buffer_size` to determine if it is valid.
+    pub shim_verify: unsafe extern "efiapi" fn(buffer: *mut c_void, buffer_size: u32) -> Status,
+    /// Unused function that is defined by the shim.
+    _generate_header: *mut c_void,
+    /// Unused function that is defined by the shim.
+    _read_header: *mut c_void,
+}
+
+impl ShimSupport {
+    /// GUID for the shim lock protocol.
+    const SHIM_LOCK_GUID: Guid = guid!("605dab50-e046-4300-abb6-3dd810dd8b23");
+    /// GUID for the shim image loader protocol.
+    const SHIM_IMAGE_LOADER_GUID: Guid = guid!("1f492041-fadb-4e59-9e57-7cafe73a55ab");
+
+    /// Determines whether the shim is loaded.
+    pub fn loaded() -> Result<bool> {
+        Ok(utils::find_handle(&Self::SHIM_LOCK_GUID)
+            .context("unable to find shim lock protocol")?
+            .is_some())
+    }
+
+    /// Determines whether the shim loader is available.
+    pub fn loader_available() -> Result<bool> {
+        Ok(utils::find_handle(&Self::SHIM_IMAGE_LOADER_GUID)
+            .context("unable to find shim image loader protocol")?
+            .is_some())
+    }
+
+    /// Use the shim to validate the `input`, returning [ShimVerificationOutput] when complete.
+    pub fn validate(input: ShimInput) -> Result<ShimVerificationOutput> {
+        // Acquire the handle to the shim lock protocol.
+        let handle = utils::find_handle(&Self::SHIM_LOCK_GUID)
+            .context("unable to find shim lock protocol")?
+            .ok_or_else(|| anyhow!("unable to find shim lock protocol"))?;
+        // Acquire the protocol exclusively to the shim lock.
+        let protocol = uefi::boot::open_protocol_exclusive::<ShimLockProtocol>(handle)
+            .context("unable to open shim lock protocol")?;
+
+        // If the input type is a device path, we need to load the data.
+        let maybe_loaded_data = match input {
+            ShimInput::OwnedDataBuffer(_, _data) => {
+                bail!("owned data buffer is not supported in the verification function");
+            }
+            ShimInput::DataBuffer(_, _) => None,
+            ShimInput::ResolvedPath(path) => Some(path.read_file()?),
+        };
+
+        // Convert the input to a buffer.
+        // If the input provides the data buffer, we will use that.
+        // Otherwise, we will use the data loaded by this function.
+        let buffer = match input {
+            ShimInput::OwnedDataBuffer(_root, _data) => {
+                bail!("owned data buffer is not supported in the verification function");
+            }
+            ShimInput::DataBuffer(_root, data) => data,
+            ShimInput::ResolvedPath(_path) => maybe_loaded_data
+                .as_deref()
+                .context("expected data buffer to be loaded already")?,
+        };
+
+        // Check if the buffer is too large to verify.
+        if buffer.len() > u32::MAX as usize {
+            bail!("buffer is too large to verify with shim lock protocol");
+        }
+
+        // Call the shim verify function.
+        // SAFETY: The shim verify function is specified by the shim lock protocol.
+        // Calling this function is considered safe because
+        let status =
+            unsafe { (protocol.shim_verify)(buffer.as_ptr() as *mut c_void, buffer.len() as u32) };
+
+        // If the verification failed, return the verification failure output.
+        if !status.is_success() {
+            return Ok(ShimVerificationOutput::VerificationFailed);
+        }
+
+        // If verification succeeded, return the validation output,
+        // which might include the loaded data.
+        Ok(maybe_loaded_data
+            .map(ShimVerificationOutput::VerifiedDataBuffer)
+            .unwrap_or(ShimVerificationOutput::VerifiedDataNotLoaded))
+    }
+
+    /// Load the image specified by the `input` and returns an image handle.
+    pub fn load(current_image: Handle, input: ShimInput) -> Result<Handle> {
+        // Determine whether the shim is loaded.
+        let shim_loaded = Self::loaded().context("unable to determine if shim is loaded")?;
+
+        // Determine whether the shim loader is available.
+        let shim_loader_available =
+            Self::loader_available().context("unable to determine if shim loader is available")?;
+
+        // Determines whether LoadImage in Boot Services must be patched.
+        // Version 16 of the shim doesn't require extra effort to load Secure Boot binaries.
+        // If the image loader is installed, we can skip over the security override.
+        let requires_security_override = shim_loaded && !shim_loader_available;
+
+        // If the security override is required, we will bail for now.
+        if requires_security_override {
+            bail!("shim image loader protocol is not available, please upgrade to shim version 16");
+        }
+
+        // Converts the shim input to an owned data buffer.
+        let input = input
+            .into_owned_data_buffer()
+            .context("unable to convert input to loaded data buffer")?;
+
+        // Constructs a LoadImageSource from the input.
+        let source = LoadImageSource::FromBuffer {
+            buffer: input.buffer().context("unable to get buffer from input")?,
+            file_path: input.file_path(),
+        };
+
+        // Loads the image using Boot Services LoadImage function.
+        uefi::boot::load_image(current_image, source).context("unable to load image")
+    }
+}

src/main.rs

@@ -16,7 +16,7 @@ use crate::platform::timer::PlatformTimer;
 use crate::secure::SecureBoot;
 use crate::utils::PartitionGuidForm;
 use anyhow::{Context, Result, bail};
-use log::{error, info};
+use log::{error, info, warn};
 use std::collections::BTreeMap;
 use std::ops::Deref;
 use std::time::Duration;
@@ -74,7 +74,7 @@ pub mod utils;
 fn run() -> Result<()> {
     // For safety reasons, we will bail early if Secure Boot is enabled.
     if SecureBoot::enabled().context("unable to determine Secure Boot status")? {
-        bail!("Secure Boot is enabled. Sprout does not currently support Secure Boot.");
+        warn!("Secure Boot is enabled. Sprout does not currently support Secure Boot.");
     }
 
     // Start the platform timer.

src/utils.rs

@@ -1,5 +1,6 @@
 use anyhow::{Context, Result};
 use std::ops::Deref;
+use uefi::boot::SearchType;
 use uefi::fs::{FileSystem, Path};
 use uefi::proto::device_path::text::{AllowShortcuts, DevicePathFromText, DisplayOnly};
 use uefi::proto::device_path::{DevicePath, PoolDevicePath};
@@ -103,6 +104,20 @@ pub struct ResolvedPath {
     pub filesystem_handle: Handle,
 }
 
+impl ResolvedPath {
+    /// Read the file specified by this path into a buffer and return it.
+    pub fn read_file(&self) -> Result<Vec<u8>> {
+        let fs = uefi::boot::open_protocol_exclusive::<SimpleFileSystem>(self.filesystem_handle)
+            .context("unable to open filesystem protocol")?;
+        let mut fs = FileSystem::new(fs);
+        let path = self
+            .sub_path
+            .to_string(DisplayOnly(false), AllowShortcuts(false))?;
+        let content = fs.read(Path::new(&path));
+        content.context("unable to read file contents")
+    }
+}
+
 /// Resolve a path specified by `input` to its various components.
 /// Uses `default_root_path` as the base root if one is not specified in the path.
 /// Returns [ResolvedPath] which contains the resolved components.
@@ -157,14 +172,7 @@ pub fn resolve_path(default_root_path: &DevicePath, input: &str) -> Result<Resol
 /// the filesystem handle protocol acquired.
 pub fn read_file_contents(default_root_path: &DevicePath, input: &str) -> Result<Vec<u8>> {
     let resolved = resolve_path(default_root_path, input)?;
-    let fs = uefi::boot::open_protocol_exclusive::<SimpleFileSystem>(resolved.filesystem_handle)
+    resolved.read_file()
-        .context("unable to open filesystem protocol")?;
-    let mut fs = FileSystem::new(fs);
-    let path = resolved
-        .sub_path
-        .to_string(DisplayOnly(false), AllowShortcuts(false))?;
-    let content = fs.read(Path::new(&path));
-    content.context("unable to read file contents")
 }
 
 /// Filter a string-like Option `input` such that an empty string is [None].
@@ -232,3 +240,25 @@ pub fn partition_guid(path: &DevicePath, form: PartitionGuidForm) -> Result<Opti
         Ok(None)
     }
 }
+
+/// Find a handle that provides the specified `protocol`.
+pub fn find_handle(protocol: &Guid) -> Result<Option<Handle>> {
+    // Locate the requested protocol handle.
+    match uefi::boot::locate_handle_buffer(SearchType::ByProtocol(protocol)) {
+        // If a handle is found, the protocol is available.
+        Ok(handles) => Ok(if handles.is_empty() {
+            None
+        } else {
+            Some(handles[0])
+        }),
+        // If an error occurs, check if it is because the protocol is not available.
+        // If so, return false. Otherwise, return the error.
+        Err(error) => {
+            if error.status() == Status::NOT_FOUND {
+                Ok(None)
+            } else {
+                Err(error).context("unable to determine if the protocol is available")
+            }
+        }
+    }
+}