OvmfPkg/Sec: Add #VC exception handling for Sec phase

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.

Before establishing the exception handling, validate that the supported
version of the SEV-ES protocol in OVMF is supported by the hypervisor.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>

2 files changed, 173 insertions, 13 deletions

diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c
index 6dea6e7..169c04b 100644
--- a/OvmfPkg/Sec/SecMain.c
+++ b/OvmfPkg/Sec/SecMain.c
@@ -24,6 +24,9 @@
 #include <Library/PeCoffExtraActionLib.h>

 #include <Library/ExtractGuidedSectionLib.h>

 #include <Library/LocalApicLib.h>

+#include <Library/CpuExceptionHandlerLib.h>

+#include <Register/Amd/Ghcb.h>

+#include <Register/Amd/Msr.h>

 

 #include <Ppi/TemporaryRamSupport.h>

 

@@ -34,6 +37,10 @@ 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 +719,120 @@ FindAndReportEntryPoints (
   return;

 }

 

+/**

+  Handle an SEV-ES/GHCB protocol check failure.

+

+  Notify the hypervisor using the VMGEXIT instruction that the SEV-ES guest

+  wishes to be terminated.

+

+  @param[in] ReasonCode  Reason code to provide to the hypervisor for the

+                         termination request.

+

+**/

+STATIC

+VOID

+SevEsProtocolFailure (

+  IN UINT8  ReasonCode

+  )

+{

+  MSR_SEV_ES_GHCB_REGISTER  Msr;

+

+  //

+  // Use the GHCB MSR Protocol to request termination by the hypervisor

+  //

+  Msr.GhcbPhysicalAddress = 0;

+  Msr.GhcbTerminate.Function = GHCB_INFO_TERMINATE_REQUEST;

+  Msr.GhcbTerminate.ReasonCodeSet = GHCB_TERMINATE_GHCB;

+  Msr.GhcbTerminate.ReasonCode = ReasonCode;

+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, Msr.GhcbPhysicalAddress);

+

+  AsmVmgExit ();

+

+  ASSERT (FALSE);

+  CpuDeadLoop ();

+}

+

+/**

+  Validate the SEV-ES/GHCB protocol level.

+

+  Verify that the level of SEV-ES/GHCB protocol supported by the hypervisor

+  and the guest intersect. If they don't intersect, request termination.

+

+**/

+STATIC

+VOID

+SevEsProtocolCheck (

+  VOID

+  )

+{

+  MSR_SEV_ES_GHCB_REGISTER  Msr;

+  GHCB                      *Ghcb;

+

+  //

+  // Use the GHCB MSR Protocol to obtain the GHCB SEV-ES Information for

+  // protocol checking

+  //

+  Msr.GhcbPhysicalAddress = 0;

+  Msr.GhcbInfo.Function = GHCB_INFO_SEV_INFO_GET;

+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, Msr.GhcbPhysicalAddress);

+

+  AsmVmgExit ();

+

+  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);

+

+  if (Msr.GhcbInfo.Function != GHCB_INFO_SEV_INFO) {

+    SevEsProtocolFailure (GHCB_TERMINATE_GHCB_GENERAL);

+  }

+

+  if (Msr.GhcbProtocol.SevEsProtocolMin > Msr.GhcbProtocol.SevEsProtocolMax) {

+    SevEsProtocolFailure (GHCB_TERMINATE_GHCB_PROTOCOL);

+  }

+

+  if ((Msr.GhcbProtocol.SevEsProtocolMin > GHCB_VERSION_MAX) ||

+      (Msr.GhcbProtocol.SevEsProtocolMax < GHCB_VERSION_MIN)) {

+    SevEsProtocolFailure (GHCB_TERMINATE_GHCB_PROTOCOL);

+  }

+

+  //

+  // SEV-ES protocol checking succeeded, set the initial GHCB address

+  //

+  Msr.GhcbPhysicalAddress = FixedPcdGet32 (PcdOvmfSecGhcbBase);

+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, Msr.GhcbPhysicalAddress);

+

+  Ghcb = Msr.Ghcb;

+  SetMem (Ghcb, sizeof (*Ghcb), 0);

+

+  //

+  // Set the version to the maximum that can be supported

+  //

+  Ghcb->ProtocolVersion = MIN (Msr.GhcbProtocol.SevEsProtocolMax, GHCB_VERSION_MAX);

+  Ghcb->GhcbUsage = GHCB_STANDARD_USAGE;

+}

+

+/**

+  Determine if SEV-ES is active.

+

+  During early booting, SEV-ES support code will set a flag to indicate that

+  SEV-ES is enabled. Return the value of this flag as an indicator that SEV-ES

+  is enabled.

+

+  @retval TRUE   SEV-ES is enabled

+  @retval FALSE  SEV-ES is not enabled

+

+**/

+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 +858,56 @@ 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;

+    UINT8  *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 ()) {

+    SevEsProtocolCheck ();

+

+    //

+    // 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 ((DEBUG_INFO,

     "SecCoreStartupWithStack(0x%x, 0x%x)\n",

     (UINT32)(UINTN)BootFv,

@@ -751,19 +920,6 @@ 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

diff --git a/OvmfPkg/Sec/SecMain.inf b/OvmfPkg/Sec/SecMain.inf
index 63ba4cb..7f78dce 100644
--- a/OvmfPkg/Sec/SecMain.inf
+++ b/OvmfPkg/Sec/SecMain.inf
@@ -50,15 +50,19 @@
   PeCoffExtraActionLib

   ExtractGuidedSectionLib

   LocalApicLib

+  CpuExceptionHandlerLib

 

 [Ppis]

   gEfiTemporaryRamSupportPpiGuid                # PPI ALWAYS_PRODUCED

 

 [Pcd]

+  gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase

   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase

   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvSize

   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvBase

   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvSize

+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBase

+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbSize

   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase

   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase

   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize