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ArmVirtPkg/HighMemDxe: preserve non-exec permissions on newly added regions 

Using DxeServices::SetMemorySpaceAttributes to set cacheability
attributes has the side effect of stripping permission attributes,
given that those are bits in the same bitfield, and so setting the
Attributes argument to EFI_MEMORY_WB implies not setting EFI_MEMORY_XP
or EFI_MEMORY_RO attributes.

In fact, the situation is even worse, given that the descriptor returned
by DxeServices::GetMemorySpaceDescriptor does not reflect the permission
attributes that may have been set by the preceding call to
DxeServices::AddMemorySpace if PcdDxeNxMemoryProtectionPolicy has been
configured to map EfiConventionalMemory with non-executable permissions.

Note that this applies equally to the non-executable stack and to PE/COFF
sections that may have been mapped with R-X or RW- permissions. This is
due to the ambiguity in the meaning of the EFI_MEMORY_RO/EFI_MEMORY_XP
attributes when used in the GCD memory map, i.e., between signifying
that an underlying RAM region has the controls to be configured as
read-only or non-executable, and signifying that the contents of a
certain UEFI memory region allow them to be mapped with certain
restricted permissions.

So let's check the policy in PcdDxeNxMemoryProtectionPolicy directly,
and set the EFI_MEMORY_XP attribute if appropriate for
EfiConventionalMemory regions.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
This commit is contained in:
Ard Biesheuvel 2017-02-28 13:45:47 +00:00
parent e9429e7997
commit 413edd4709
2 changed files with 17 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
ArmVirtPkg/HighMemDxe/HighMemDxe.c
View File

@ -37,6 +37,7 @@ InitializeHighMemDxe (
UINTN AddressCells, SizeCells;
UINT64 CurBase;
UINT64 CurSize;
UINT64 Attributes;
Status = gBS->LocateProtocol (&gFdtClientProtocolGuid, NULL,
(VOID **)&FdtClient);
@ -77,8 +78,21 @@ InitializeHighMemDxe (
continue;
}
Status = gDS->SetMemorySpaceAttributes (CurBase, CurSize,
EFI_MEMORY_WB);
//
// Take care not to strip any permission attributes that will have been
// set by DxeCore on the region we just added if a strict permission
// policy is in effect for EfiConventionalMemory regions.
// Unfortunately, we cannot interrogate the GCD memory space map for
// those permissions, since they are not recorded there (for historical
// reasons), so check the policy directly.
//
Attributes = EFI_MEMORY_WB;
if ((PcdGet64 (PcdDxeNxMemoryProtectionPolicy) &
(1U << (UINT32)EfiConventionalMemory)) != 0) {
Attributes |= EFI_MEMORY_XP;
}
Status = gDS->SetMemorySpaceAttributes (CurBase, CurSize, Attributes);
if (EFI_ERROR (Status)) {
DEBUG ((EFI_D_ERROR,

1
ArmVirtPkg/HighMemDxe/HighMemDxe.inf
View File

@ -45,6 +45,7 @@
[Pcd]
gArmTokenSpaceGuid.PcdSystemMemoryBase
gEfiMdeModulePkgTokenSpaceGuid.PcdDxeNxMemoryProtectionPolicy
[Depex]
gEfiCpuArchProtocolGuid AND gFdtClientProtocolGuid