Re: [PATCH 1/2] efi/libstub: add support for loading the initrd from a device path

[Laszlo Ersek <lersek@redhat.com>]

On 02/06/20 19:26, Heinrich Schuchardt wrote:
> On 2/6/20 3:03 PM, Ard Biesheuvel wrote:

>> +    status = efi_bs_call(handle_protocol, handle, &lf2_proto_guid,
>> +                 (void **)&lf2);
>> +    if (status != EFI_SUCCESS)
>> +        return status;
> 
> You require here that there is a handle exposing the device path
> protocol with the initrd specific device path. On the same handle the
> EFI_LOAD_FILE2_PROTOCOL must be installed which will load the initrd
> file when called with the same device path.
> 
> An alternative implementation would simple loop over all instances of
> the EFI_LOAD_FILE2_PROTOCOL and try to load the initrd.

That's not a great idea IMO. EFI_LOAD_FILE2_PROTOCOL instances take
device-specific filenames / pathnames to load. If you pass any
particular pathname (e.g. "initrd" or "\\initrd") to random
EFI_LOAD_FILE2_PROTOCOL instance in the protocol database, there could
be undesired results / side effects. (It could cause network activity,
for example.)

Sticking with a VenMedia (i.e. GUID-ed) devpath is much safer; it
practically lets us define our own device-specific filename / pathname
space. (And in my other email, I suggested "use an empty devpath" for
device-specific pathname, because that's the simplest, it looks
spec-conformat, and it's safe, because our GUID makes the load attempt
unique already.)

I do agree with your question though: "Please, indicate which software
you expect to expose the initrd related EFI_LOAD_FILE2_PROTOCOL."

Thanks
Laszlo