Re: EFI_PXE_BASE_CODE_PROTOCOL

[Leif Lindholm <leif.lindholm@linaro.org>]

+Peter Jones (sorry Peter)

On Tue, Aug 06, 2019 at 08:34:58AM +0200, Heinrich Schuchardt wrote:
> iPXE uses the EFI simple network protocol to execute DHCP.

OK.

> Can GRUB already do the same when the EFI_PXE_BASE_CODE_PROTOCOL is not
> present?

Yes. As of very recently (proper* DHCP support was only merged in
March 2019, so is included in 2.04 release, prior to that it
technically performed BOOTP).

SNP means you do your own networking - it gives you access to the raw
(usually) Ethernet packets.

* proper as in "it now conceptually does the correct thing", not as in
  "I have extensively tested this".

> What I do not understand about GRUB's grub_net_configure_by_dhcp_ack()
> is that it silently assumes IPv4 being used without even checking. This
> contradicts the definition of the PXE base code protocol in the UEFI
> standard:

Well, it would not surprise me if this function predates GRUB's UEFI
support.

It actually gets even slightly messier when you look at what GRUB does
when netbooting itself; it starts out using MNP (and hence IP
addresses assigned by UEFI) to load its modules, switching to SNP once
it loads efinet.mod.

> EFI_PXE_BASE_CODE_PACKET DhcpAck is a union:
> 
> typedef union {
>  UINT8                             Raw[1472];
>  EFI_PXE_BASE_CODE_DHCPV4_PACKET   Dhcpv4;
>  EFI_PXE_BASE_CODE_DHCPV6_PACKET   Dhcpv6;
> } EFI_PXE_BASE_CODE_PACKET;
> 
> Should the check be done in grub_efi_net_config_real()?

Possibly. I've cc:d Peter since he's the last person I know who took a
proper look at this.

Certainly, it would be useful if you could raise a bug on Savannah on
the ipv4 assumption.

Best Regards,

Leif