1 files changed, 73 insertions, 0 deletions
diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 29368ac69221..aded10662020 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -740,3 +740,76 @@ char *efi_convert_cmdline(efi_system_table_t *sys_table_arg,
 	*cmd_line_len = options_bytes;
 	return (char *)cmdline_addr;
 }
+
+/*
+ * Handle calling ExitBootServices according to the requirements set out by the
+ * spec.  Obtains the current memory map, and returns that info after calling
+ * ExitBootServices.  The client must specify a function to perform any
+ * processing of the memory map data prior to ExitBootServices.  A client
+ * specific structure may be passed to the function via priv.  The client
+ * function may be called multiple times.
+ */
+efi_status_t efi_exit_boot_services(efi_system_table_t *sys_table_arg,
+				    void *handle,
+				    struct efi_boot_memmap *map,
+				    void *priv,
+				    efi_exit_boot_map_processing priv_func)
+{
+	efi_status_t status;
+
+	status = efi_get_memory_map(sys_table_arg, map);
+
+	if (status != EFI_SUCCESS)
+		goto fail;
+
+	status = priv_func(sys_table_arg, map, priv);
+	if (status != EFI_SUCCESS)
+		goto free_map;
+
+	status = efi_call_early(exit_boot_services, handle, *map->key_ptr);
+
+	if (status == EFI_INVALID_PARAMETER) {
+		/*
+		 * The memory map changed between efi_get_memory_map() and
+		 * exit_boot_services().  Per the UEFI Spec v2.6, Section 6.4:
+		 * EFI_BOOT_SERVICES.ExitBootServices we need to get the
+		 * updated map, and try again.  The spec implies one retry
+		 * should be sufficent, which is confirmed against the EDK2
+		 * implementation.  Per the spec, we can only invoke
+		 * get_memory_map() and exit_boot_services() - we cannot alloc
+		 * so efi_get_memory_map() cannot be used, and we must reuse
+		 * the buffer.  For all practical purposes, the headroom in the
+		 * buffer should account for any changes in the map so the call
+		 * to get_memory_map() is expected to succeed here.
+		 */
+		*map->map_size = *map->buff_size;
+		status = efi_call_early(get_memory_map,
+					map->map_size,
+					*map->map,
+					map->key_ptr,
+					map->desc_size,
+					map->desc_ver);
+
+		/* exit_boot_services() was called, thus cannot free */
+		if (status != EFI_SUCCESS)
+			goto fail;
+
+		status = priv_func(sys_table_arg, map, priv);
+		/* exit_boot_services() was called, thus cannot free */
+		if (status != EFI_SUCCESS)
+			goto fail;
+
+		status = efi_call_early(exit_boot_services, handle, *map->key_ptr);
+	}
+
+	/* exit_boot_services() was called, thus cannot free */
+	if (status != EFI_SUCCESS)
+		goto fail;
+
+	return EFI_SUCCESS;
+
+free_map:
+	efi_call_early(free_pool, *map->map);
+fail:
+	return status;
+}