Re: [edk2-devel] MdeModulePkg: Fix MAT SplitRecord() Logic introduce one bug and will cause SUT reset when boot to windows

["Oliver Smith-Denny" <osde@linux.microsoft.com>]

On 4/18/2024 6:56 AM, Huang, Yanbo wrote:
> The PCD PcdPlatformEfiRtCodeMemorySize is used in https://github.com/tianocore/edk2-platforms/blob/master/Platform/Intel/MinPlatformPkg/PlatformInit/PlatformInitPei/PlatformInitPreMem.c
> This PCD seems defined the size allocated for run time services code, and the similar PCD is PcdPlatformEfiRtDataMemorySize, seems defined the size allocated for run time services data.
> I guess dandan means if the runtime services code size is small than the PCD defined, then the " Extra EfiRuntimeServicesCode regions which aren't part of loaded runtime images." size should be FixedPcdGet32 (PcdPlatformEfiRtCodeMemorySize) - the actual runtime image code size?
> 

Drawing the lines here, we will lie in the EFI_MEMORY_MAP to say that
all bin memory is allocated, regardless of this PCD:

https://github.com/tianocore/edk2/blob/0afb8743493853e30171f6000de51242e22a1eb8/MdeModulePkg/Core/Dxe/Mem/Page.c#L1973-L1989

So this is just junk unallocated memory that we are reporting as
a type it *could* be if an allocation occurs to minimize failures
of ExitBootServices. Which is questionable. But in terms of
attributes, I would expect we either have this unallocated
memory marked the same as the bin type or better, mark it RP
if we can (Taylor is making a change to set RP on free memory
by default, so we would have this in the page table, but we
would need to decide what we tell the OS).

Going back to the questionableness of this: can we not report
the entire bin as allocated memory to the OS? I understand
what the comment is saying; I don't like that we will lie to
the OS and reserve larger chunks of runtime memory than we
actually need and that will get the wrong permissions set on
it (for example making this garbage data be executable).

Thanks,
Oliver


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