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MdeModulePkg: DxeCore: Adding check for underflow before subtraction

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During DXE core memory service initialization, the system would check
available resource descriptor hobs against the memory top from PHIT hob.
However, it is possible that a given resource descriptor hob will not be
larger than the cover the memory top, causing the Length calculation to
underflow.

This change adds a check for potential underflow before performing the
subtraction.

Signed-off-by: Kun Qin <kun.qin@microsoft.com>
This commit is contained in:
Kun Qin 2025-10-30 11:42:53 -07:00 • committed by mergify[bot]
parent 5be1bccd9c
commit feeb137d43
1 changed files with 8 additions and 2 deletions
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10
MdeModulePkg/Core/Dxe/Gcd/Gcd.c
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@ -2430,8 +2430,14 @@ CoreInitializeMemoryServices (
//
Attributes = PhitResourceHob->ResourceAttribute;
BaseAddress = PageAlignAddress (PhitHob->EfiMemoryTop);
Length = PageAlignLength (ResourceHobMemoryTop - BaseAddress);
FindLargestFreeRegion (&BaseAddress, &Length, (EFI_HOB_MEMORY_ALLOCATION *)GetFirstHob (EFI_HOB_TYPE_MEMORY_ALLOCATION));
if (BaseAddress > ResourceHobMemoryTop) {
Length = 0;
} else {
Length = PageAlignLength (ResourceHobMemoryTop - BaseAddress);
FindLargestFreeRegion (&BaseAddress, &Length, (EFI_HOB_MEMORY_ALLOCATION *)GetFirstHob (EFI_HOB_TYPE_MEMORY_ALLOCATION));
}
if (Length < MinimalMemorySizeNeeded) {
//
// If that range is not large enough to intialize the DXE Core, then