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-rw-r--r--src/boot/efi/linux.c155
1 files changed, 155 insertions, 0 deletions
diff --git a/src/boot/efi/linux.c b/src/boot/efi/linux.c
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+++ b/src/boot/efi/linux.c
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+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+/*
+ * Generic Linux boot protocol using the EFI/PE entry point of the kernel. Passes
+ * initrd with the LINUX_INITRD_MEDIA_GUID DevicePath and cmdline with
+ * EFI LoadedImageProtocol.
+ *
+ * This method works for Linux 5.8 and newer on ARM/Aarch64, x86/x68_64 and RISC-V.
+ */
+
+#include <efi.h>
+#include <efilib.h>
+
+#include "initrd.h"
+#include "linux.h"
+#include "pe.h"
+#include "secure-boot.h"
+#include "util.h"
+
+#define STUB_PAYLOAD_GUID \
+ { 0x55c5d1f8, 0x04cd, 0x46b5, { 0x8a, 0x20, 0xe5, 0x6c, 0xbb, 0x30, 0x52, 0xd0 } }
+
+typedef struct {
+ const void *addr;
+ size_t len;
+ const EFI_DEVICE_PATH *device_path;
+} ValidationContext;
+
+static bool validate_payload(
+ const void *ctx, const EFI_DEVICE_PATH *device_path, const void *file_buffer, size_t file_size) {
+
+ const ValidationContext *payload = ASSERT_PTR(ctx);
+
+ if (device_path != payload->device_path)
+ return false;
+
+ /* Security arch (1) protocol does not provide a file buffer. Instead we are supposed to fetch the payload
+ * ourselves, which is not needed as we already have everything in memory and the device paths match. */
+ if (file_buffer && (file_buffer != payload->addr || file_size != payload->len))
+ return false;
+
+ return true;
+}
+
+static EFI_STATUS load_image(EFI_HANDLE parent, const void *source, size_t len, EFI_HANDLE *ret_image) {
+ assert(parent);
+ assert(source);
+ assert(ret_image);
+
+ /* We could pass a NULL device path, but it's nicer to provide something and it allows us to identify
+ * the loaded image from within the security hooks. */
+ struct {
+ VENDOR_DEVICE_PATH payload;
+ EFI_DEVICE_PATH end;
+ } _packed_ payload_device_path = {
+ .payload = {
+ .Header = {
+ .Type = MEDIA_DEVICE_PATH,
+ .SubType = MEDIA_VENDOR_DP,
+ .Length = { sizeof(payload_device_path.payload), 0 },
+ },
+ .Guid = STUB_PAYLOAD_GUID,
+ },
+ .end = {
+ .Type = END_DEVICE_PATH_TYPE,
+ .SubType = END_ENTIRE_DEVICE_PATH_SUBTYPE,
+ .Length = { sizeof(payload_device_path.end), 0 },
+ },
+ };
+
+ /* We want to support unsigned kernel images as payload, which is safe to do under secure boot
+ * because it is embedded in this stub loader (and since it is already running it must be trusted). */
+ install_security_override(
+ validate_payload,
+ &(ValidationContext) {
+ .addr = source,
+ .len = len,
+ .device_path = &payload_device_path.payload.Header,
+ });
+
+ EFI_STATUS ret = BS->LoadImage(
+ /*BootPolicy=*/false,
+ parent,
+ &payload_device_path.payload.Header,
+ (void *) source,
+ len,
+ ret_image);
+
+ uninstall_security_override();
+
+ return ret;
+}
+
+EFI_STATUS linux_exec(
+ EFI_HANDLE parent,
+ const char16_t *cmdline,
+ const void *linux_buffer,
+ size_t linux_length,
+ const void *initrd_buffer,
+ size_t initrd_length) {
+
+ uint32_t compat_address;
+ EFI_STATUS err;
+
+ assert(parent);
+ assert(linux_buffer && linux_length > 0);
+ assert(initrd_buffer || initrd_length == 0);
+
+ err = pe_kernel_info(linux_buffer, &compat_address);
+#if defined(__i386__) || defined(__x86_64__)
+ if (err == EFI_UNSUPPORTED)
+ /* Kernel is too old to support LINUX_INITRD_MEDIA_GUID, try the deprecated EFI handover
+ * protocol. */
+ return linux_exec_efi_handover(
+ parent,
+ cmdline,
+ linux_buffer,
+ linux_length,
+ initrd_buffer,
+ initrd_length);
+#endif
+ if (err != EFI_SUCCESS)
+ return log_error_status_stall(err, u"Bad kernel image: %r", err);
+
+ _cleanup_(unload_imagep) EFI_HANDLE kernel_image = NULL;
+ err = load_image(parent, linux_buffer, linux_length, &kernel_image);
+ if (err != EFI_SUCCESS)
+ return log_error_status_stall(err, u"Error loading kernel image: %r", err);
+
+ EFI_LOADED_IMAGE_PROTOCOL *loaded_image;
+ err = BS->HandleProtocol(kernel_image, &LoadedImageProtocol, (void **) &loaded_image);
+ if (err != EFI_SUCCESS)
+ return log_error_status_stall(err, u"Error getting kernel loaded image protocol: %r", err);
+
+ if (cmdline) {
+ loaded_image->LoadOptions = (void *) cmdline;
+ loaded_image->LoadOptionsSize = strsize16(loaded_image->LoadOptions);
+ }
+
+ _cleanup_(cleanup_initrd) EFI_HANDLE initrd_handle = NULL;
+ err = initrd_register(initrd_buffer, initrd_length, &initrd_handle);
+ if (err != EFI_SUCCESS)
+ return log_error_status_stall(err, u"Error registering initrd: %r", err);
+
+ err = BS->StartImage(kernel_image, NULL, NULL);
+
+ /* Try calling the kernel compat entry point if one exists. */
+ if (err == EFI_UNSUPPORTED && compat_address > 0) {
+ EFI_IMAGE_ENTRY_POINT compat_entry =
+ (EFI_IMAGE_ENTRY_POINT) ((uint8_t *) loaded_image->ImageBase + compat_address);
+ err = compat_entry(kernel_image, ST);
+ }
+
+ return log_error_status_stall(err, u"Error starting kernel image: %r", err);
+}