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UefiCpuPkg: Always Initialize Separate AP Exception Stacks

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Today, CpuMpPei and CpuDxe only initialize separate exception
stacks for the APs when PcdCpuStackGuard is enabled so that
if a stack overflow occurs, hitting the guard page, the exception
can be handler with a separate stack.

However, this operation also creates a separate GDT for each AP.
This is a safer option than all APs sharing the BSP's GDT because
there are issues with concurrent access to the structures contained
within. Furthermore, even when a stack guard page is not present,
stack overflows can still occur and corrupt the stack; if an
exception is taken here, it is still valuable to have a separate
exception stack for sanity.

This commit updates CpuMpPei and CpuDxe to always create separate
exception stacks for the APs (and therefore separate GDTs).

Signed-off-by: Oliver Smith-Denny <osde@microsoft.com>
This commit is contained in:
Oliver Smith-Denny 2025-09-26 09:43:44 -07:00 • committed by mergify[bot]
parent f64b4065b7
commit e67f405713
3 changed files with 4 additions and 10 deletions
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1
UefiCpuPkg/CpuDxe/CpuDxe.inf
View file

@ -89,7 +89,6 @@
[Pcd]
gEfiMdeModulePkgTokenSpaceGuid.PcdPteMemoryEncryptionAddressOrMask ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdHeapGuardPropertyMask ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdNullPointerDetectionPropertyMask ## CONSUMES
gEfiMdeModulePkgTokenSpaceGuid.PcdTdxSharedBitMask ## CONSUMES

6
UefiCpuPkg/CpuDxe/CpuMp.c
View file

@ -761,11 +761,9 @@ InitializeMpExceptionHandlers (
}
//
// Setup stack switch for Stack Guard feature.
// Setup stack switch for Stack Guard feature and separate AP GDTs.
//
if (PcdGetBool (PcdCpuStackGuard)) {
InitializeMpExceptionStackSwitchHandlers ();
}
InitializeMpExceptionStackSwitchHandlers ();
}
/**

7
UefiCpuPkg/CpuMpPei/CpuMpPei.c
View file

@ -68,7 +68,8 @@ InitializeExceptionStackSwitchHandlers (
}
/**
Initializes MP exceptions handlers for the sake of stack switch requirement.
Initializes MP exceptions handlers for the sake of stack switch requirement and giving the APs
their own GDTs.
This function will allocate required resources required to setup stack switch
and pass them through SwitchStackData to each logic processor.
@ -86,10 +87,6 @@ InitializeMpExceptionStackSwitchHandlers (
EFI_STATUS Status;
UINT8 *Buffer;
if (!PcdGetBool (PcdCpuStackGuard)) {
return;
}
Status = MpInitLibGetNumberOfProcessors (&NumberOfProcessors, NULL);
ASSERT_EFI_ERROR (Status);