Re: [Xen-devel] [PATCH v2 6/6] multiboot2: Do not pass memory maps to image if EFI boot services are enabled

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Tue, Aug 11, 2015 at 02:59:56PM -0400, Konrad Rzeszutek Wilk wrote:
> On Mon, Jul 20, 2015 at 04:35:54PM +0200, Daniel Kiper wrote:
> > Do not pass memory maps to image if it asked for EFI boot services. Maps are
> > usually invalid in that case and they can confuse potential user. Image 
> > should
> > get memory map itself just before ExitBootServices() call.
>
> Can we point to some commits in Linux or Xen in which these situations
> arose?
>
> Wait, I think there even was one commit in grub.
>
> Aha:
>
> ommit e75fdee420a7ad95e9a465c9699adc2e2e970440
> Author: Vladimir 'phcoder' Serbinenko <phcoder@xxxxxxxxx>
> Date:   Tue Mar 26 11:34:56 2013 +0100
>
>         * grub-core/kern/efi/mm.c (grub_efi_finish_boot_services):
>         Try terminating EFI services several times due to quirks in some
>         implementations.
>
> Otherwise:
>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Nope, this is a bit different problem. In general GRUB2 assumes that
EFI boot services memory regions are free and specify them as such
in relevant maps. However, this is not true if you jump into loaded
image with EFI boot services enabled. So, we should not expose this
maps to the user when he/she asked for access to EFI boot services.
This is not very big issue for him/her because he/she can get memory
map from EFI just before ExitBootServices() call. This way they will
have latest valid memory map.

Daniel

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