OvmfPkg/BaseMemEncryptLib: use the SEV_STATUS MSR value from workarea

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3582

Improve the MemEncryptSev{Es,Snp}IsEnabled() to use the SEV_STATUS MSR
value saved in the workarea. Since workarea is valid until the PEI phase,
so, for the Dxe phase use the PcdConfidentialComputingGuestAttr to
determine which SEV technology is enabled.

Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Acked-by: Jiewen Yao <jiewen.yao@intel.com>

OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf

@@ -58,3 +58,4 @@
 
 [Pcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdPteMemoryEncryptionAddressOrMask
+  gEfiMdePkgTokenSpaceGuid.PcdConfidentialComputingGuestAttr

OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLibInternal.c

@@ -16,83 +16,84 @@
 #include <Register/Amd/Msr.h>
 #include <Register/Cpuid.h>
 #include <Uefi/UefiBaseType.h>
+#include <ConfidentialComputingGuestAttr.h>
 
-STATIC BOOLEAN  mSevStatus        = FALSE;
+STATIC UINT64   mCurrentAttr            = 0;
-STATIC BOOLEAN  mSevEsStatus      = FALSE;
+STATIC BOOLEAN  mCurrentAttrRead        = FALSE;
-STATIC BOOLEAN  mSevSnpStatus     = FALSE;
-STATIC BOOLEAN  mSevStatusChecked = FALSE;
-
 STATIC UINT64   mSevEncryptionMask      = 0;
 STATIC BOOLEAN  mSevEncryptionMaskSaved = FALSE;
 
 /**
-  Reads and sets the status of SEV features.
+  The function check if the specified Attr is set.
 
-  **/
+  @param[in]  CurrentAttr   The current attribute.
+  @param[in]  Attr          The attribute to check.
+
+  @retval  TRUE      The specified Attr is set.
+  @retval  FALSE     The specified Attr is not set.
+
+**/
 STATIC
-VOID
+BOOLEAN
-EFIAPI
+AmdMemEncryptionAttrCheck (
-InternalMemEncryptSevStatus (
+  IN  UINT64                             CurrentAttr,
-  VOID
+  IN  CONFIDENTIAL_COMPUTING_GUEST_ATTR  Attr
   )
 {
-  UINT32                            RegEax;
+  switch (Attr) {
-  MSR_SEV_STATUS_REGISTER           Msr;
+    case CCAttrAmdSev:
-  CPUID_MEMORY_ENCRYPTION_INFO_EAX  Eax;
-  BOOLEAN                           ReadSevMsr;
-  UINT64                            EncryptionMask;
-
-  ReadSevMsr = FALSE;
-
-  EncryptionMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask);
-  if (EncryptionMask != 0) {
       //
-    // The MSR has been read before, so it is safe to read it again and avoid
+      // SEV is automatically enabled if SEV-ES or SEV-SNP is active.
-    // having to validate the CPUID information.
       //
-    ReadSevMsr = TRUE;
+      return CurrentAttr >= CCAttrAmdSev;
-  } else {
+    case CCAttrAmdSevEs:
       //
-    // Check if memory encryption leaf exist
+      // SEV-ES is automatically enabled if SEV-SNP is active.
       //
-    AsmCpuid (CPUID_EXTENDED_FUNCTION, &RegEax, NULL, NULL, NULL);
+      return CurrentAttr >= CCAttrAmdSevEs;
-    if (RegEax >= CPUID_MEMORY_ENCRYPTION_INFO) {
+    case CCAttrAmdSevSnp:
-      //
+      return CurrentAttr == CCAttrAmdSevSnp;
-      // CPUID Fn8000_001F[EAX] Bit 1 (Sev supported)
+    default:
-      //
+      return FALSE;
-      AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, &Eax.Uint32, NULL, NULL, NULL);
-
-      if (Eax.Bits.SevBit) {
-        ReadSevMsr = TRUE;
-      }
-    }
   }
+}
 
-  if (ReadSevMsr) {
+/**
+  Check if the specified confidential computing attribute is active.
+
+  @param[in]  Attr          The attribute to check.
+
+  @retval TRUE   The specified Attr is active.
+  @retval FALSE  The specified Attr is not active.
+
+**/
+STATIC
+BOOLEAN
+EFIAPI
+ConfidentialComputingGuestHas (
+  IN  CONFIDENTIAL_COMPUTING_GUEST_ATTR  Attr
+  )
+{
   //
-    // Check MSR_0xC0010131 Bit 0 (Sev Enabled)
+  // Get the current CC attribute.
   //
-    Msr.Uint32 = AsmReadMsr32 (MSR_SEV_STATUS);
+  // We avoid reading the PCD on every check because this routine could be indirectly
-    if (Msr.Bits.SevBit) {
+  // called during the virtual pointer conversion. And its not safe to access the
-      mSevStatus = TRUE;
+  // PCDs during the virtual pointer conversion.
+  //
+  if (!mCurrentAttrRead) {
+    mCurrentAttr     = PcdGet64 (PcdConfidentialComputingGuestAttr);
+    mCurrentAttrRead = TRUE;
   }
 
   //
-    // Check MSR_0xC0010131 Bit 1 (Sev-Es Enabled)
+  // If attr is for the AMD group then call AMD specific checks.
   //
-    if (Msr.Bits.SevEsBit) {
+  if (((RShiftU64 (mCurrentAttr, 8)) & 0xff) == 1) {
-      mSevEsStatus = TRUE;
+    return AmdMemEncryptionAttrCheck (mCurrentAttr, Attr);
   }
 
-    //
+  return (mCurrentAttr == Attr);
-    // Check MSR_0xC0010131 Bit 2 (Sev-Snp Enabled)
-    //
-    if (Msr.Bits.SevSnpBit) {
-      mSevSnpStatus = TRUE;
-    }
-  }
-
-  mSevStatusChecked = TRUE;
 }
 
 /**
@@ -107,11 +108,7 @@ MemEncryptSevSnpIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
+  return ConfidentialComputingGuestHas (CCAttrAmdSevSnp);
-    InternalMemEncryptSevStatus ();
-  }
-
-  return mSevSnpStatus;
 }
 
 /**
@@ -126,11 +123,7 @@ MemEncryptSevEsIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
+  return ConfidentialComputingGuestHas (CCAttrAmdSevEs);
-    InternalMemEncryptSevStatus ();
-  }
-
-  return mSevEsStatus;
 }
 
 /**
@@ -145,11 +138,7 @@ MemEncryptSevIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
+  return ConfidentialComputingGuestHas (CCAttrAmdSev);
-    InternalMemEncryptSevStatus ();
-  }
-
-  return mSevStatus;
 }
 
 /**

OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf

@@ -58,6 +58,7 @@
 
 [FixedPcd]
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedEnd

OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLibInternal.c

@@ -17,82 +17,51 @@
 #include <Register/Cpuid.h>
 #include <Uefi/UefiBaseType.h>
 
-STATIC BOOLEAN  mSevStatus        = FALSE;
-STATIC BOOLEAN  mSevEsStatus      = FALSE;
-STATIC BOOLEAN  mSevSnpStatus     = FALSE;
-STATIC BOOLEAN  mSevStatusChecked = FALSE;
-
-STATIC UINT64   mSevEncryptionMask      = 0;
-STATIC BOOLEAN  mSevEncryptionMaskSaved = FALSE;
-
 /**
-  Reads and sets the status of SEV features.
+   Read the workarea to determine whether SEV is enabled. If enabled,
+   then return the SevEsWorkArea pointer.
 
   **/
 STATIC
-VOID
+SEC_SEV_ES_WORK_AREA *
+EFIAPI
+GetSevEsWorkArea (
+  VOID
+  )
+{
+  OVMF_WORK_AREA  *WorkArea;
+
+  WorkArea = (OVMF_WORK_AREA *)FixedPcdGet32 (PcdOvmfWorkAreaBase);
+
+  //
+  // If its not SEV guest then SevEsWorkArea is not valid.
+  //
+  if ((WorkArea == NULL) || (WorkArea->Header.GuestType != GUEST_TYPE_AMD_SEV)) {
+    return NULL;
+  }
+
+  return (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
+}
+
+/**
+  Read the SEV Status MSR value from the workarea
+
+  **/
+STATIC
+UINT32
 EFIAPI
 InternalMemEncryptSevStatus (
   VOID
   )
 {
-  UINT32                            RegEax;
-  MSR_SEV_STATUS_REGISTER           Msr;
-  CPUID_MEMORY_ENCRYPTION_INFO_EAX  Eax;
-  BOOLEAN                           ReadSevMsr;
   SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
 
-  ReadSevMsr = FALSE;
+  SevEsWorkArea = GetSevEsWorkArea ();
-
+  if (SevEsWorkArea == NULL) {
-  SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
+    return 0;
-  if ((SevEsWorkArea != NULL) && (SevEsWorkArea->EncryptionMask != 0)) {
-    //
-    // The MSR has been read before, so it is safe to read it again and avoid
-    // having to validate the CPUID information.
-    //
-    ReadSevMsr = TRUE;
-  } else {
-    //
-    // Check if memory encryption leaf exist
-    //
-    AsmCpuid (CPUID_EXTENDED_FUNCTION, &RegEax, NULL, NULL, NULL);
-    if (RegEax >= CPUID_MEMORY_ENCRYPTION_INFO) {
-      //
-      // CPUID Fn8000_001F[EAX] Bit 1 (Sev supported)
-      //
-      AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, &Eax.Uint32, NULL, NULL, NULL);
-
-      if (Eax.Bits.SevBit) {
-        ReadSevMsr = TRUE;
-      }
-    }
   }
 
-  if (ReadSevMsr) {
+  return (UINT32)(UINTN)SevEsWorkArea->SevStatusMsrValue;
-    //
-    // Check MSR_0xC0010131 Bit 0 (Sev Enabled)
-    //
-    Msr.Uint32 = AsmReadMsr32 (MSR_SEV_STATUS);
-    if (Msr.Bits.SevBit) {
-      mSevStatus = TRUE;
-    }
-
-    //
-    // Check MSR_0xC0010131 Bit 1 (Sev-Es Enabled)
-    //
-    if (Msr.Bits.SevEsBit) {
-      mSevEsStatus = TRUE;
-    }
-
-    //
-    // Check MSR_0xC0010131 Bit 2 (Sev-Snp Enabled)
-    //
-    if (Msr.Bits.SevSnpBit) {
-      mSevSnpStatus = TRUE;
-    }
-  }
-
-  mSevStatusChecked = TRUE;
 }
 
 /**
@@ -107,11 +76,11 @@ MemEncryptSevSnpIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
+  MSR_SEV_STATUS_REGISTER  Msr;
-    InternalMemEncryptSevStatus ();
-  }
 
-  return mSevSnpStatus;
+  Msr.Uint32 = InternalMemEncryptSevStatus ();
+
+  return Msr.Bits.SevSnpBit ? TRUE : FALSE;
 }
 
 /**
@@ -126,11 +95,11 @@ MemEncryptSevEsIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
+  MSR_SEV_STATUS_REGISTER  Msr;
-    InternalMemEncryptSevStatus ();
-  }
 
-  return mSevEsStatus;
+  Msr.Uint32 = InternalMemEncryptSevStatus ();
+
+  return Msr.Bits.SevEsBit ? TRUE : FALSE;
 }
 
 /**
@@ -145,11 +114,11 @@ MemEncryptSevIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
+  MSR_SEV_STATUS_REGISTER  Msr;
-    InternalMemEncryptSevStatus ();
-  }
 
-  return mSevStatus;
+  Msr.Uint32 = InternalMemEncryptSevStatus ();
+
+  return Msr.Bits.SevBit ? TRUE : FALSE;
 }
 
 /**
@@ -163,24 +132,12 @@ MemEncryptSevGetEncryptionMask (
   VOID
   )
 {
-  if (!mSevEncryptionMaskSaved) {
   SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
 
-    SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
+  SevEsWorkArea = GetSevEsWorkArea ();
-    if (SevEsWorkArea != NULL) {
+  if (SevEsWorkArea == NULL) {
-      mSevEncryptionMask = SevEsWorkArea->EncryptionMask;
+    return 0;
-    } else {
-      CPUID_MEMORY_ENCRYPTION_INFO_EBX  Ebx;
-
-      //
-      // CPUID Fn8000_001F[EBX] Bit 0:5 (memory encryption bit position)
-      //
-      AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, NULL, &Ebx.Uint32, NULL, NULL);
-      mSevEncryptionMask = LShiftU64 (1, Ebx.Bits.PtePosBits);
   }
 
-    mSevEncryptionMaskSaved = TRUE;
+  return SevEsWorkArea->EncryptionMask;
-  }
-
-  return mSevEncryptionMask;
 }

OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf

@@ -52,3 +52,4 @@
 
 [FixedPcd]
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase

OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c

@@ -18,7 +18,33 @@
 #include <Uefi/UefiBaseType.h>
 
 /**
-  Reads and sets the status of SEV features.
+   Read the workarea to determine whether SEV is enabled. If enabled,
+   then return the SevEsWorkArea pointer.
+
+  **/
+STATIC
+SEC_SEV_ES_WORK_AREA *
+EFIAPI
+GetSevEsWorkArea (
+  VOID
+  )
+{
+  OVMF_WORK_AREA  *WorkArea;
+
+  WorkArea = (OVMF_WORK_AREA *)FixedPcdGet32 (PcdOvmfWorkAreaBase);
+
+  //
+  // If its not SEV guest then SevEsWorkArea is not valid.
+  //
+  if ((WorkArea == NULL) || (WorkArea->Header.GuestType != GUEST_TYPE_AMD_SEV)) {
+    return NULL;
+  }
+
+  return (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
+}
+
+/**
+  Read the SEV Status MSR value from the workarea
 
   **/
 STATIC
@@ -28,38 +54,14 @@ InternalMemEncryptSevStatus (
   VOID
   )
 {
-  UINT32                            RegEax;
-  CPUID_MEMORY_ENCRYPTION_INFO_EAX  Eax;
-  BOOLEAN                           ReadSevMsr;
   SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
 
-  ReadSevMsr = FALSE;
+  SevEsWorkArea = GetSevEsWorkArea ();
-
+  if (SevEsWorkArea == NULL) {
-  SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
+    return 0;
-  if ((SevEsWorkArea != NULL) && (SevEsWorkArea->EncryptionMask != 0)) {
-    //
-    // The MSR has been read before, so it is safe to read it again and avoid
-    // having to validate the CPUID information.
-    //
-    ReadSevMsr = TRUE;
-  } else {
-    //
-    // Check if memory encryption leaf exist
-    //
-    AsmCpuid (CPUID_EXTENDED_FUNCTION, &RegEax, NULL, NULL, NULL);
-    if (RegEax >= CPUID_MEMORY_ENCRYPTION_INFO) {
-      //
-      // CPUID Fn8000_001F[EAX] Bit 1 (Sev supported)
-      //
-      AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, &Eax.Uint32, NULL, NULL, NULL);
-
-      if (Eax.Bits.SevBit) {
-        ReadSevMsr = TRUE;
-      }
-    }
   }
 
-  return ReadSevMsr ? AsmReadMsr32 (MSR_SEV_STATUS) : 0;
+  return (UINT32)(UINTN)SevEsWorkArea->SevStatusMsrValue;
 }
 
 /**
@@ -130,22 +132,14 @@ MemEncryptSevGetEncryptionMask (
   VOID
   )
 {
-  CPUID_MEMORY_ENCRYPTION_INFO_EBX  Ebx;
   SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
-  UINT64                            EncryptionMask;
 
-  SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
+  SevEsWorkArea = GetSevEsWorkArea ();
-  if (SevEsWorkArea != NULL) {
+  if (SevEsWorkArea == NULL) {
-    EncryptionMask = SevEsWorkArea->EncryptionMask;
+    return 0;
-  } else {
-    //
-    // CPUID Fn8000_001F[EBX] Bit 0:5 (memory encryption bit position)
-    //
-    AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, NULL, &Ebx.Uint32, NULL, NULL);
-    EncryptionMask = LShiftU64 (1, Ebx.Bits.PtePosBits);
   }
 
-  return EncryptionMask;
+  return SevEsWorkArea->EncryptionMask;
 }
 
 /**