[edk2-devel] [PATCH RFC v2 19/28] OvmfPkg: register GHCB gpa for the SEV-SNP guest

[Brijesh Singh]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275

The SEV-SNP guest requires that GHCB GPA must be registered before using.
The GHCB GPA can be registred using the GhcbGPARegister().

Cc: James Bottomley <jejb at linux.ibm.com>
Cc: Min Xu <min.m.xu at intel.com>
Cc: Jiewen Yao <jiewen.yao at intel.com>
Cc: Tom Lendacky <thomas.lendacky at amd.com>
Cc: Jordan Justen <jordan.l.justen at intel.com>
Cc: Ard Biesheuvel <ardb+tianocore at kernel.org>
Cc: Laszlo Ersek <lersek at redhat.com>
Cc: Erdem Aktas <erdemaktas at google.com>
Signed-off-by: Brijesh Singh <brijesh.singh at amd.com>
---
 OvmfPkg/PlatformPei/AmdSev.c        |  8 +++
 OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
 OvmfPkg/Sec/SecMain.c               | 76 ++++++++++++++++++++
 3 files changed, 85 insertions(+)

diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
index 81e40e0889..54b07622b4 100644
--- a/OvmfPkg/PlatformPei/AmdSev.c
+++ b/OvmfPkg/PlatformPei/AmdSev.c
@@ -14,6 +14,7 @@
 #include <Library/DebugLib.h>
 #include <Library/HobLib.h>
 #include <Library/MemEncryptSevLib.h>
+#include <Library/GhcbRegisterLib.h>
 #include <Library/MemoryAllocationLib.h>
 #include <Library/PcdLib.h>
 #include <PiPei.h>
@@ -156,6 +157,13 @@ AmdSevEsInitialize (
     "SEV-ES is enabled, %lu GHCB backup pages allocated starting at 0x%p\n",
     (UINT64)GhcbBackupPageCount, GhcbBackupBase));
 
+  if (MemEncryptSevSnpIsEnabled ()) {
+    //
+    // SEV-SNP guest requires that GHCB GPA must be registered before using it.
+    //
+    GhcbRegister (GhcbBasePa);
+  }
+
   AsmWriteMsr64 (MSR_SEV_ES_GHCB, GhcbBasePa);
 
   //
diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index 89c8e9627c..e9a10146ef 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -52,6 +52,7 @@
   BaseLib
   CacheMaintenanceLib
   DebugLib
+  GhcbRegisterLib
   HobLib
   IoLib
   PciLib
diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c
index 9db67e17b2..7c9650ba8f 100644
--- a/OvmfPkg/Sec/SecMain.c
+++ b/OvmfPkg/Sec/SecMain.c
@@ -750,6 +750,76 @@ SevEsProtocolFailure (
   CpuDeadLoop ();
 }
 
+/**
+  Determine if SEV-SNP is active. There is a MemEncryptIsSnpEnabled() in MemEncryptSevLib
+  but we can not use it because the SEV-SNP check need to be done before the
+  ProcessLibraryConstructorList() is called.
+
+  @retval TRUE   SEV-SNP is enabled
+  @retval FALSE  SEV-SNP is not enabled
+
+**/
+STATIC
+BOOLEAN
+SevSnpIsEnabled (
+  VOID
+  )
+{
+  SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
+
+  SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *) FixedPcdGet32 (PcdSevEsWorkAreaBase);
+
+  return ((SevEsWorkArea != NULL) && (SevEsWorkArea->SevSnpEnabled != 0));
+}
+
+/**
+ The GHCB GPA registeration need to be done before the ProcessLibraryConstructorList()
+ is called. So use a local implementation instead of including the GhcbRegisterLib.
+
+ */
+STATIC
+VOID
+SevSnpGhcbRegister (
+  UINTN   Address
+  )
+{
+  MSR_SEV_ES_GHCB_REGISTER  Msr;
+  MSR_SEV_ES_GHCB_REGISTER  CurrentMsr;
+  EFI_PHYSICAL_ADDRESS      GuestFrameNumber;
+
+  GuestFrameNumber = Address >> EFI_PAGE_SHIFT;
+
+  //
+  // Save the current MSR Value
+  //
+  CurrentMsr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
+
+  //
+  // Use the GHCB MSR Protocol to request to register the GPA.
+  //
+  Msr.GhcbPhysicalAddress = 0;
+  Msr.GhcbGpaRegister.Function = GHCB_INFO_GHCB_GPA_REGISTER_REQUEST;
+  Msr.GhcbGpaRegister.GuestFrameNumber = GuestFrameNumber;
+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, Msr.GhcbPhysicalAddress);
+
+  AsmVmgExit ();
+
+  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
+
+  //
+  // If hypervisor responded with a different GPA than requested then fail.
+  //
+  if ((Msr.GhcbGpaRegister.Function != GHCB_INFO_GHCB_GPA_REGISTER_RESPONSE) ||
+      (Msr.GhcbGpaRegister.GuestFrameNumber != GuestFrameNumber)) {
+    SevEsProtocolFailure (GHCB_TERMINATE_GHCB_GENERAL);
+  }
+
+  //
+  // Restore the MSR
+  //
+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, CurrentMsr.GhcbPhysicalAddress);
+}
+
 /**
   Validate the SEV-ES/GHCB protocol level.
 
@@ -791,6 +861,12 @@ SevEsProtocolCheck (
     SevEsProtocolFailure (GHCB_TERMINATE_GHCB_PROTOCOL);
   }
 
+  if (SevSnpIsEnabled ()) {
+    //
+    // SEV-SNP guest requires that GHCB GPA must be registered before using it.
+    //
+    SevSnpGhcbRegister (FixedPcdGet32 (PcdOvmfSecGhcbBase));
+  }
   //
   // SEV-ES protocol checking succeeded, set the initial GHCB address
   //
-- 
2.17.1



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