On Thu, 28 Nov 2024 at 11:21, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > On Thu, 28 Nov 2024 at 11:00, Johan Hovold <johan@xxxxxxxxxx> wrote: > > > > On Thu, Nov 28, 2024 at 09:52:33AM +0100, Ard Biesheuvel wrote: > > > ... > > > In upstream EDK2, the map key is just a monotonic counter that gets > > > incremented on every memory map update, so one experiment worth > > > conducting is to repeat the second call to ExitBootServices() a couple > > > of times, increasing the map key each time. > > > > I had already tried repeating the second call (GMM + EBS) by running it > > in a loop, and I do see the map_key increasing for each iteration (e.g. > > by 0x1a). > > > > > Or use GetMemoryMap() to > > > just grab the map key without the actual memory map, and printing it > > > to the console (although the timer is disabled on the first call so > > > anything that relies on that will be shut down at this point) > > > > I just tried adding another inner loop just calling GetMemoryMap() a few > > times and I see the map_key increasing there too for each iteration > > (e.g. by 0x6). > > > > (The map size remains constant.) > > > > I do get the feeling that efi_printk() contributes to the memory map > > updates, and I can indeed get the reference design fw to similarly fail > > if I try to print the map_key after each call to GetMemoryMap() in a > > retry loop. > > Per the spec, the only thing you are permitted to call if > ExitBootServices() fails is GetMemoryMap(), and so this is not a spec > violation. > > If GetMemoryMap() itself causes the map key to assume a different > value than the one it returns, or if ExitBootServices() invokes event > callbacks on the second call that may cause the map key to get updated > before it manages to check it, there is obviously something wrong in > the firmware implementation. If you're happy to experiment more, you could try and register a notification for EFI_EVENT_GROUP_BEFORE_EXIT_BOOT_SERVICES using CreateEventEx(), and see if it gets called when ExitBootServices() is called. That would at least help narrow it down.
