[PATCH v3 07/12] efi: payload: always shutdown barebox when booting

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

When barebox is about to boot a kernel image, it calls shutdown_barebox
and then starts the image. When the kernel image is wrapped in a UKI,
barebox will not detect it as a kernel image and will thus not call
shutdown_barebox beforehand, which can mean that e.g. state is not
flushed.

We do not want to treat UKIs completely like kernels (e.g. we do not
want to override their built-in bootargs), but we still want to properly
shutdown barebox.

Resolve this by shutting down barebox whenever we are in a bootm handler,
no matter which kind of image is about to be started: bootm is the point
of no return. Images run from the shell via binfmt keep returning to
barebox afterwards, with the exception of EFI-stubbed kernels, which take
over the machine and thus continue to shut barebox down as before.

Assisted-by: Claude:opus-5
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 .../efi-payload-bootm-shutdown.rst            | 10 +++++++++
 efi/payload/bootm.c                           |  4 ++--
 efi/payload/image.c                           | 21 +++++++++++++------
 efi/payload/image.h                           |  1 +
 4 files changed, 28 insertions(+), 8 deletions(-)
 create mode 100644 Documentation/migration-guides/migration-master/efi-payload-bootm-shutdown.rst

diff --git a/Documentation/migration-guides/migration-master/efi-payload-bootm-shutdown.rst b/Documentation/migration-guides/migration-master/efi-payload-bootm-shutdown.rst
new file mode 100644
index 000000000000..2e0a84b536e6
--- /dev/null
+++ b/Documentation/migration-guides/migration-master/efi-payload-bootm-shutdown.rst
@@ -0,0 +1,10 @@
+EFI applications booted via bootm no longer return to barebox
+-------------------------------------------------------------
+
+When barebox runs as EFI payload, :ref:`command_bootm` now shuts down
+barebox before starting any EFI application, not only EFI-stubbed Linux
+kernels. If the application returns, barebox exits to the firmware instead
+of returning to the shell or trying the next boot entry.
+
+EFI applications that are expected to return, like an EFI shell, should be
+executed directly from the shell instead.
diff --git a/efi/payload/bootm.c b/efi/payload/bootm.c
index d6a79f0c7795..58b7dd5ea779 100644
--- a/efi/payload/bootm.c
+++ b/efi/payload/bootm.c
@@ -185,7 +185,7 @@ static int do_bootm_efi_stub(struct image_data *data)
 	if (data->dryrun)
 		goto unload_ramdisk;
 
-	ret = efi_execute_image(handle, loaded_image, type);
+	ret = efi_execute_image(handle, loaded_image, true, type);
 
 	/* efi_execute_image takes care to unload the image on error,
 	 * so we set image_freed and fall through to freeing ramdisk
@@ -225,7 +225,7 @@ static int efi_app_execute(struct image_data *data)
 		return 0;
 	}
 
-	return efi_execute_image(handle, loaded_image, type);
+	return efi_execute_image(handle, loaded_image, true, type);
 }
 
 static int linux_efi_handover = true;
diff --git a/efi/payload/image.c b/efi/payload/image.c
index 76aca1c43cec..4e59c7b4ea10 100644
--- a/efi/payload/image.c
+++ b/efi/payload/image.c
@@ -100,17 +100,26 @@ int efi_load_image(const char *file, struct efi_loaded_image **loaded_image,
 
 int efi_execute_image(efi_handle_t handle,
 		      struct efi_loaded_image *loaded_image,
+		      bool is_bootm,
 		      enum filetype filetype)
 {
 	efi_status_t efiret;
 	const char *options;
-	bool is_driver, is_kernel = false;
+	bool is_driver;
+	bool no_return;
 
 	is_driver = (loaded_image->image_code_type == EFI_BOOT_SERVICES_CODE) ||
 		(loaded_image->image_code_type == EFI_RUNTIME_SERVICES_CODE);
  
 	efi_export_dtb();
 
+	/*
+	 * A bootm handler is the point of no return, but an EFI-stubbed kernel
+	 * started from the shell takes over the machine just the same, so
+	 * barebox needs to be shut down in both cases.
+	 */
+	no_return = is_bootm || filetype_is_linux_efi_image(filetype);
+
 	if (filetype_is_linux_efi_image(filetype)) {
 		options = linux_bootargs_get();
 		printf("Booting kernel via StartImage");
@@ -121,11 +130,11 @@ int efi_execute_image(efi_handle_t handle,
 				(strlen(options) + 1) * sizeof(wchar_t);
 		}
 		printf("...\n");
+	}
 
+	if (no_return) {
 		efi_set_variable_usec("LoaderTimeExecUSec", &efi_systemd_vendor_guid,
 				      ktime_to_us(ktime_get()));
-
-		is_kernel = true;
 		shutdown_barebox();
 	}
 
@@ -135,8 +144,8 @@ int efi_execute_image(efi_handle_t handle,
 
 	efi_continue_devices();
 
-	if (is_kernel) {
-		pr_emerg("Kernel image has unexpectedly returned\n");
+	if (no_return) {
+		pr_emerg("Boot image has unexpectedly returned\n");
 		BS->exit(efi_parent_image, efiret, 0, NULL);
 	}
 
@@ -162,7 +171,7 @@ static int efi_execute(struct binfmt_hook *b, char *file, int argc, char **argv)
 	if (ret)
 		return ret;
 
-	return efi_execute_image(handle, loaded_image, b->type);
+	return efi_execute_image(handle, loaded_image, false, b->type);
 }
 
 static struct binfmt_hook binfmt_efi_hook = {
diff --git a/efi/payload/image.h b/efi/payload/image.h
index bab1be368c21..33f7e1a21b30 100644
--- a/efi/payload/image.h
+++ b/efi/payload/image.h
@@ -13,6 +13,7 @@ int efi_load_image(const char *file, struct efi_loaded_image **loaded_image,
 
 int efi_execute_image(efi_handle_t handle,
 		      struct efi_loaded_image *loaded_image,
+		      bool is_bootm,
 		      enum filetype filetype);
 
 extern struct image_handler efi_x86_linux_handle_tr;
-- 
2.47.3