[PATCH v4 32/40] OvmfPkg/Sec: Add #VC exception handling for Sec phase

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198

An SEV-ES guest will generate a #VC exception when it encounters a
non-automatic exit (NAE) event. It is expected that the #VC exception
handler will communicate with the hypervisor using the GHCB to handle
the NAE event.

NAE events can occur during the Sec phase, so initialize exception
handling early in the OVMF Sec support.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 OvmfPkg/Sec/SecMain.inf |  2 ++
 OvmfPkg/Sec/SecMain.c   | 76 ++++++++++++++++++++++++++++++++++-------
 2 files changed, 65 insertions(+), 13 deletions(-)

diff --git a/OvmfPkg/Sec/SecMain.inf b/OvmfPkg/Sec/SecMain.inf
index 63ba4cb555fb..401d06039dd3 100644
--- a/OvmfPkg/Sec/SecMain.inf
+++ b/OvmfPkg/Sec/SecMain.inf
@@ -50,11 +50,13 @@ [LibraryClasses]
   PeCoffExtraActionLib
   ExtractGuidedSectionLib
   LocalApicLib
+  CpuExceptionHandlerLib
 
 [Ppis]
   gEfiTemporaryRamSupportPpiGuid                # PPI ALWAYS_PRODUCED
 
 [Pcd]
+  gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvBase
diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c
index bae9764577f0..2bab7128ade2 100644
--- a/OvmfPkg/Sec/SecMain.c
+++ b/OvmfPkg/Sec/SecMain.c
@@ -24,6 +24,7 @@
 #include <Library/PeCoffExtraActionLib.h>
 #include <Library/ExtractGuidedSectionLib.h>
 #include <Library/LocalApicLib.h>
+#include <Library/CpuExceptionHandlerLib.h>
 
 #include <Ppi/TemporaryRamSupport.h>
 
@@ -34,6 +35,10 @@ typedef struct _SEC_IDT_TABLE {
   IA32_IDT_GATE_DESCRIPTOR  IdtTable[SEC_IDT_ENTRY_COUNT];
 } SEC_IDT_TABLE;
 
+typedef struct _SEC_SEV_ES_WORK_AREA {
+  UINT8  SevEsEnabled;
+} SEC_SEV_ES_WORK_AREA;
+
 VOID
 EFIAPI
 SecStartupPhase2 (
@@ -712,6 +717,19 @@ FindAndReportEntryPoints (
   return;
 }
 
+STATIC
+BOOLEAN
+SevEsIsEnabled (
+  VOID
+  )
+{
+  SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
+
+  SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *) FixedPcdGet32 (PcdSevEsWorkAreaBase);
+
+  return ((SevEsWorkArea != NULL) && (SevEsWorkArea->SevEsEnabled != 0));
+}
+
 VOID
 EFIAPI
 SecCoreStartupWithStack (
@@ -737,8 +755,53 @@ SecCoreStartupWithStack (
     Table[Index] = 0;
   }
 
+  //
+  // Initialize IDT - Since this is before library constructors are called,
+  // we use a loop rather than CopyMem.
+  //
+  IdtTableInStack.PeiService = NULL;
+  for (Index = 0; Index < SEC_IDT_ENTRY_COUNT; Index ++) {
+    UINT8  *Src, *Dst;
+    UINTN  Byte;
+
+    Src = (UINT8 *) &mIdtEntryTemplate;
+    Dst = (UINT8 *) &IdtTableInStack.IdtTable[Index];
+    for (Byte = 0; Byte < sizeof (mIdtEntryTemplate); Byte++) {
+      Dst[Byte] = Src[Byte];
+    }
+  }
+
+  IdtDescriptor.Base  = (UINTN)&IdtTableInStack.IdtTable;
+  IdtDescriptor.Limit = (UINT16)(sizeof (IdtTableInStack.IdtTable) - 1);
+
+  if (SevEsIsEnabled()) {
+    //
+    // For SEV-ES guests, the exception handler is needed before calling
+    // ProcessLibraryConstructorList() because some of the library constructors
+    // perform some functions that result in #VC exceptions being generated.
+    //
+    // Due to this code executing before library constructors, *all* library
+    // API calls are theoretically interface contract violations. However,
+    // because this is SEC (executing in flash), those constructors cannot
+    // write variables with static storage duration anyway. Furthermore, only
+    // a small, restricted set of APIs, such as AsmWriteIdtr() and
+    // InitializeCpuExceptionHandlers(), are called, where we require that the
+    // underlying library not require constructors to have been invoked and
+    // that the library instance not trigger any #VC exceptions.
+    //
+    AsmWriteIdtr (&IdtDescriptor);
+    InitializeCpuExceptionHandlers (NULL);
+  }
+
   ProcessLibraryConstructorList (NULL, NULL);
 
+  if (!SevEsIsEnabled()) {
+    //
+    // For non SEV-ES guests, just load the IDTR.
+    //
+    AsmWriteIdtr (&IdtDescriptor);
+  }
+
   DEBUG ((EFI_D_INFO,
     "SecCoreStartupWithStack(0x%x, 0x%x)\n",
     (UINT32)(UINTN)BootFv,
@@ -751,19 +814,6 @@ SecCoreStartupWithStack (
   //
   InitializeFloatingPointUnits ();
 
-  //
-  // Initialize IDT
-  //
-  IdtTableInStack.PeiService = NULL;
-  for (Index = 0; Index < SEC_IDT_ENTRY_COUNT; Index ++) {
-    CopyMem (&IdtTableInStack.IdtTable[Index], &mIdtEntryTemplate, sizeof (mIdtEntryTemplate));
-  }
-
-  IdtDescriptor.Base  = (UINTN)&IdtTableInStack.IdtTable;
-  IdtDescriptor.Limit = (UINT16)(sizeof (IdtTableInStack.IdtTable) - 1);
-
-  AsmWriteIdtr (&IdtDescriptor);
-
 #if defined (MDE_CPU_X64)
   //
   // ASSERT that the Page Tables were set by the reset vector code to
-- 
2.17.1