[PATCH v1 12/14] bootm: efi: boot signed EFI images when signed images are forced

[Johannes Schneider <johannes.schneider@leica-geosystems.com>]

With signed images forced, bootm refuses everything but FIT images. Let
EFI images through when Authenticode support is built in, and have the
EFI loader verify them against the "efi" keyring before loading:
mandatory with signed images forced or bootm.verify=signature, skipped
with bootm.verify=none, reported otherwise.

Not when barebox itself runs as EFI payload: its EFI application
handler passes the image to the firmware's LoadImage() and verifies
nothing itself.

An image booted this way is verified twice: here, so that barebox does
not parse anything of an image that is not authenticated, and again in
LoadImage(), which verifies every image a payload loads and cannot rely
on an earlier verdict. Skipping either would need the result of the
first carried over to the second, a shortcut that has to stay correct
as both paths change; the second verification costs 70 ms for a 30 MiB
UKI on an i.MX8MP.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com>
---
 common/bootm.c     |  6 +++++-
 efi/loader/bootm.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/common/bootm.c b/common/bootm.c
index 27da1a590b..c8fc5220a6 100644
--- a/common/bootm.c
+++ b/common/bootm.c
@@ -576,7 +576,11 @@ struct image_data *bootm_boot_prep(const struct bootm_data *bootm_data)
 		 */
 		data->oftree_file = NULL;
 		data->initrd_file = NULL;
-		if (data->image_type != filetype_fit) {
+		if (data->image_type == filetype_exe &&
+		    IS_ENABLED(CONFIG_EFI_LOADER_AUTHENTICODE) &&
+		    !efi_is_payload()) {
+			/* authenticated by the EFI loader before it runs */
+		} else if (data->image_type != filetype_fit) {
 			pr_err("Signed boot and image is no FIT image, aborting\n");
 			ret = -EINVAL;
 			goto err_out;
diff --git a/efi/loader/bootm.c b/efi/loader/bootm.c
index 8a83865458..fa12caf560 100644
--- a/efi/loader/bootm.c
+++ b/efi/loader/bootm.c
@@ -35,6 +35,7 @@
 #include <efi/error.h>
 #include <efi/initrd.h>
 #include <efi/devicepath.h>
+#include <efi/loader/authenticode.h>
 #include <efi/loader/pe.h>
 #include <loadable.h>
 
@@ -195,6 +196,30 @@ static efi_status_t efi_install_initrd(struct image_data *data,
 	return EFI_SUCCESS;
 }
 
+static int efi_loader_verify(struct image_data *data, void *efi, size_t size)
+{
+	bool required = bootm_signed_images_are_forced() ||
+			data->verify == BOOTM_VERIFY_SIGNATURE;
+	int ret;
+
+	if (!IS_ENABLED(CONFIG_EFI_LOADER_AUTHENTICODE)) {
+		if (required) {
+			pr_err("signed image required, but no Authenticode support\n");
+			return -EPERM;
+		}
+		return 0;
+	}
+
+	if (!required && data->verify == BOOTM_VERIFY_NONE)
+		return 0;
+
+	ret = efi_authenticode_verify(efi, size, EFI_AUTHENTICODE_KEYRING);
+	if (ret && required)
+		return -EPERM;
+
+	return 0;
+}
+
 /* The image may sit in a much larger partition: load only the image */
 static const struct resource *efi_load_os(struct image_data *data,
 					  resource_size_t start,
@@ -266,6 +291,10 @@ static int efi_loader_bootm(struct image_data *data)
 		return -EINVAL;
 	}
 
+	ret = efi_loader_verify(data, (void *)os_res->start, size);
+	if (ret)
+		return ret;
+
 	/* systemd-stub passes the load options on as kernel command line */
 	if (filetype_is_linux_efi_image(data->kernel_type) ||
 	    efi_pe_find_section((void *)os_res->start, size, ".linux",
-- 
2.43.0