chore(eficore): decouple the shim support from the image load callsites

crates/eficore/src/loader.rs

@@ -0,0 +1,141 @@
+use crate::loader::source::ImageSource;
+use crate::secure::SecureBoot;
+use crate::shim::hook::SecurityHook;
+use crate::shim::{ShimInput, ShimSupport};
+use anyhow::{Context, Result, bail};
+use log::warn;
+use uefi::Handle;
+use uefi::boot::LoadImageSource;
+
+/// Represents EFI image sources generically.
+pub mod source;
+
+/// Handle to a loaded EFI image.
+pub struct ImageHandle {
+    /// Handle to the loaded image.
+    handle: Handle,
+}
+
+impl ImageHandle {
+    /// Create a new image handle based on a handle from the UEFI stack.
+    pub fn new(handle: Handle) -> Self {
+        Self { handle }
+    }
+
+    /// Retrieve the underlying handle.
+    pub fn handle(&self) -> &Handle {
+        &self.handle
+    }
+}
+
+/// Request to load an image from a source, with support for additional validation features.
+pub struct ImageLoadRequest<'source> {
+    /// Handle to the current image.
+    current_image: Handle,
+    /// Source of the image to load.
+    source: ImageSource<'source>,
+}
+
+impl<'source> ImageLoadRequest<'source> {
+    /// Create a new image load request with a current image and a source.
+    pub fn new(current_image: Handle, source: ImageSource<'source>) -> Self {
+        Self {
+            current_image,
+            source,
+        }
+    }
+
+    /// Retrieve the current image.
+    pub fn current_image(&self) -> &Handle {
+        &self.current_image
+    }
+
+    /// Retrieve the source of the image to load.
+    pub fn source(&'source self) -> &'source ImageSource<'source> {
+        &self.source
+    }
+
+    /// Convert the request into a source.
+    pub fn into_source(self) -> ImageSource<'source> {
+        self.source
+    }
+}
+
+/// EFI image loader.
+pub struct ImageLoader;
+
+impl ImageLoader {
+    /// Load an image using the image `request` which allows
+    pub fn load(request: ImageLoadRequest) -> Result<ImageHandle> {
+        // Determine whether Secure Boot is enabled.
+        let secure_boot =
+            SecureBoot::enabled().context("unable to determine if secure boot is enabled")?;
+
+        // Determine whether the shim is loaded.
+        let shim_loaded = ShimSupport::loaded().context("unable to determine if shim is loaded")?;
+
+        // Determine whether the shim loader is available.
+        let shim_loader_available = ShimSupport::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 hook.
+        let requires_security_hook = secure_boot && shim_loaded && !shim_loader_available;
+
+        // If the security hook is required, we will bail for now.
+        if requires_security_hook {
+            // Install the security hook, if possible. If it's not, this is necessary to continue,
+            // so we should bail.
+            let installed = SecurityHook::install().context("unable to install security hook")?;
+            if !installed {
+                bail!("unable to install security hook required for this platform");
+            }
+        }
+
+        // If the shim is loaded, we will need to retain the shim protocol to allow
+        // loading multiple images.
+        if shim_loaded {
+            // Retain the shim protocol after loading the image.
+            ShimSupport::retain()?;
+        }
+
+        // Clone the current image handle to use for loading the image.
+        let current_image = *request.current_image();
+
+        // Converts the source to a shim input with an owned data buffer.
+        let input = ShimInput::from(request.into_source())
+            .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.
+        let result = uefi::boot::load_image(current_image, source).context("unable to load image");
+
+        // If the security override is required, we will uninstall the security hook.
+        if requires_security_hook {
+            let uninstall_result = crate::shim::hook::SecurityHook::uninstall();
+            // Ensure we don't mask load image errors if uninstalling fails.
+            if result.is_err()
+                && let Err(uninstall_error) = &uninstall_result
+            {
+                // Warn on the error since the load image error is more important.
+                warn!("unable to uninstall security hook: {}", uninstall_error);
+            } else {
+                // Otherwise, ensure we handle the original uninstallation result.
+                uninstall_result?;
+            }
+        }
+
+        // Assert the result and grab the handle.
+        let handle = result?;
+
+        // Retrieve the handle from the result and make a new image handle.
+        Ok(ImageHandle::new(handle))
+    }
+}