[PATCH] UefiCpuPkg/CpuDxe: fix incorrect check of SMM mode

[Jian J Wang <jian.j.wang@intel.com>]

Current IsInSmm() method makes use of gEfiSmmBase2ProtocolGuid.InSmm() to
check if current processor is in SMM mode or not. But this is not correct
because gEfiSmmBase2ProtocolGuid.InSmm() can only detect if the caller is
running in SMRAM or from SMM driver. It cannot guarantee if the caller is
running in SMM mode. Because SMM mode will load its own page table, adding
an extra check of saved DXE page table base address against current CR3
register value can help to get the correct answer for sure (in SMM mode or
not in SMM mode).

This is an issue caused by check-in at

  d106cf71eabaacff63c14626a4a87346b93074dd

Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
---
 UefiCpuPkg/CpuDxe/CpuPageTable.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/UefiCpuPkg/CpuDxe/CpuPageTable.c b/UefiCpuPkg/CpuDxe/CpuPageTable.c
index 850eed60e7..df021798c0 100644
--- a/UefiCpuPkg/CpuDxe/CpuPageTable.c
+++ b/UefiCpuPkg/CpuDxe/CpuPageTable.c
@@ -136,7 +136,14 @@ IsInSmm (
     mSmmBase2->InSmm (mSmmBase2, &InSmm);
   }
 
-  return InSmm;
+  //
+  // mSmmBase2->InSmm() can only detect if the caller is running in SMRAM
+  // or from SMM driver. It cannot tell if the caller is running in SMM mode.
+  // Check page table base address to guarantee that because SMM mode willl
+  // load its own page table.
+  //
+  return (InSmm &&
+          mPagingContext.ContextData.X64.PageTableBase != (UINT64)AsmReadCr3());
 }
 
 /**
-- 
2.16.2.windows.1