On 3/2/2018 7:45 PM, Laszlo Ersek wrote:
On 03/02/18 06:58, Jian J Wang wrote:
if PcdDxeNxMemoryProtectionPolicy is enabled for EfiReservedMemoryType
of memory, #PF will be triggered for each APs after ExitBootServices
in SCRT test. The root cause is that AP wakeup code executed at that
time is stored in memory of type EfiReservedMemoryType (referenced by
global mReservedApLoopFunc), which is marked as non-executable.

This patch fixes this issue by setting memory of mReservedApLoopFunc to
be executable immediately after allocation.

Cc: Ruiyu Ni <ruiyu...@intel.com>
Cc: Eric Dong <eric.d...@intel.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.w...@intel.com>
  UefiCpuPkg/Library/MpInitLib/DxeMpLib.c | 15 +++++++++++++++
  1 file changed, 15 insertions(+)

diff --git a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c 
index fd2317924f..5fcb08677c 100644
--- a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
@@ -399,6 +399,21 @@ InitMpGlobalData (
    ASSERT_EFI_ERROR (Status);
+  //
+  // Make sure that the buffer memory is executable.
+  //
+  Status = gDS->GetMemorySpaceDescriptor (Address, &MemDesc);
+  if (!EFI_ERROR (Status)) {
+    gDS->SetMemorySpaceAttributes (
+           Address,
+             CpuMpData->AddressMap.RelocateApLoopFuncSize
+             )),
+           MemDesc.Attributes & (~EFI_MEMORY_XP)
+           );
+  }
    mReservedApLoopFunc = (VOID *) (UINTN) Address;
    ASSERT (mReservedApLoopFunc != NULL);
    mReservedTopOfApStack = (UINTN) Address + EFI_PAGES_TO_SIZE 
(EFI_SIZE_TO_PAGES (ApSafeBufferSize));

Honestly, I see little point in the "Dxe Nx Memory Protection Policy"
when we then override it *every time* it gets in our way.
"RelocateApLoopFuncSize" is likely significantly smaller than a full
page, so we're making a good chunk of the "safe stack(s)" executable too.

Anyway, can you perhaps check BIT0 (standing for EfiReservedMemoryType)
in PcdDxeNxMemoryProtectionPolicy, to see if the above hack is necessary?


Checking PCD is not very good I think.
If checking is really needed, how about check MemDesc.Attributes EFI_MEMORY_XP bit?

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