[PATCH v2 1/2] xen/efi: Handle cases where file didn't come from ESP

[Frediano Ziglio <frediano.ziglio@xxxxxxxxx>]

A boot loader can load files from outside ESP.
In these cases device could be not provided or path could
be something not supported.
In these cases allows to boot anyway, all information
could be provided using UKI or using other boot loader
features.

Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
---
Changes since v1:
- set "leaf" to NULL instead of a buffer with an empty string;
- keep read_file fatal if cannot load file (except configuration).
---
 xen/common/efi/boot.c | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index 1a9b4e7dae..b18af2f1f4 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -443,6 +443,18 @@ static EFI_FILE_HANDLE __init get_parent_handle(const 
EFI_LOADED_IMAGE *loaded_i
     CHAR16 *pathend, *ptr;
     EFI_STATUS ret;
 
+    /*
+     * In some cases the image could not come from a specific device.
+     * For instance this can happen if Xen was loaded using GRUB2 "linux"
+     * command.
+     */
+    *leaf = NULL;
+    if ( !loaded_image->DeviceHandle )
+    {
+        PrintStr(L"Xen image loaded without providing a device\r\n");
+        return NULL;
+    }
+
     do {
         EFI_FILE_IO_INTERFACE *fio;
 
@@ -466,7 +478,15 @@ static EFI_FILE_HANDLE __init get_parent_handle(const 
EFI_LOADED_IMAGE *loaded_i
 
         if ( DevicePathType(dp) != MEDIA_DEVICE_PATH ||
              DevicePathSubType(dp) != MEDIA_FILEPATH_DP )
-            blexit(L"Unsupported device path component");
+        {
+            /*
+             * The image could come from an unsupported device.
+             * For instance this can happen if Xen was loaded using GRUB2
+             * "chainloader" command and the file was not from ESP.
+             */
+            PrintStr(L"Unsupported device path component\r\n");
+            return NULL;
+        }
 
         if ( *buffer )
         {
@@ -772,8 +792,11 @@ static bool __init read_file(EFI_FILE_HANDLE dir_handle, 
CHAR16 *name,
 
     if ( !name )
         PrintErrMesg(L"No filename", EFI_OUT_OF_RESOURCES);
-    ret = dir_handle->Open(dir_handle, &FileHandle, name,
-                           EFI_FILE_MODE_READ, 0);
+    if ( dir_handle )
+        ret = dir_handle->Open(dir_handle, &FileHandle, name,
+                               EFI_FILE_MODE_READ, 0);
+    else
+        ret = EFI_NOT_FOUND;
     if ( file == &cfg && ret == EFI_NOT_FOUND )
         return false;
     if ( EFI_ERROR(ret) )
@@ -1404,7 +1427,7 @@ void EFIAPI __init noreturn efi_start(EFI_HANDLE 
ImageHandle,
         /* Read and parse the config file. */
         if ( read_section(loaded_image, L"config", &cfg, NULL) )
             PrintStr(L"Using builtin config file\r\n");
-        else if ( !cfg_file_name )
+        else if ( !cfg_file_name && file_name)
         {
             CHAR16 *tail;
 
@@ -1515,7 +1538,8 @@ void EFIAPI __init noreturn efi_start(EFI_HANDLE 
ImageHandle,
         efi_bs->FreePages(cfg.addr, PFN_UP(cfg.size));
         cfg.addr = 0;
 
-        dir_handle->Close(dir_handle);
+        if ( dir_handle )
+            dir_handle->Close(dir_handle);
 
         if ( gop && !base_video )
         {
-- 
2.43.0