I think there is a couple of issues with the current implementation of
CoreExitBootServices:
1 . According to ExitBootServices() description, events of type
EVT_SIGNAL_EXIT_BOOT_SERVICES, must be signaled once even if ExitBootServices()
is called multiple times.
Current implementation signals events more than once if ExitBootServices() is
called more than once.
2. Since CoreTerminateMemoryMap, which validates MapKey, is called prior to
signaling exit-boot-services events, memory map changes introduced by the event
handlers are not getting detected.
It means, there is a chance that OS loader will successfully transition to
runtime with an outdated memory map.
Technically exit-boot-services callbacks are not supposed to alter memory map.
However, it is very difficult for a driver writer to predict if a particular
UEFI API such as GetVariable or HandleProtocol would alter a memory map.
I believe CoreExitBootServices implementation should detect such memory map
changes and report them back to OS loader by returning
EFI_INVALID_PARAMETER(MapKey is incorrect).
Thanks,
Felix
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