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

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Tue, Jun 24, 2025 at 03:27:08PM +0100, Frediano Ziglio wrote:
> 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@cloud.com>

Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

> ---
> 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
> 

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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