[RFC PATCH 12/19] OvmfPkg/MemEncryptSevLib: Add support to validate system RAM

["Brijesh Singh" <brijesh.singh@amd.com>]

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

Many of the integrity guarantees of SEV-SNP are enforced through the
Reverse Map Table (RMP). Each RMP entry contains the GPA at which a
particular page of DRAM should be mapped. The guest can request the
hypervisor to add pages in the RMP table via the Page State Change VMGEXIT
defined in the GHCB specification section 2.5.1 and 4.1.6. Inside each RMP
entry is a Validated flag; this flag is automatically cleared to 0 by the
CPU hardware when a new RMP entry is created for a guest. Each VM page
can be either validated or invalidated, as indicated by the Validated
flag in the RMP entry. Memory access to a private page that is not
validated generates a #VC. A VM can use the PVALIDATE instruction to
validate the private page before using it.

During the guest creation, the boot ROM memory is pre-validated by the
AMD-SEV firmware. The MemEncryptSevSnpValidateSystemRam() can be called
during the SEC and PEI phase to validate the detected system RAM.

One of the fields in the Page State Change NAE is the RMP page size. The
page size input parameter indicates that either a 4KB or 2MB page should
be used while adding the RMP entry. During the validation, when possible,
the MemEncryptSevSnpValidateSystemRam() will use the 2MB entry. A
hypervisor backing the memory may choose to use the different page size
in the RMP entry. In those cases, the PVALIDATE instruction should return
SIZEMISMATCH. If a SIZEMISMATCH is detected, then validate all 512-pages
constituting a 2MB region.

Upon completion, the PVALIDATE instruction sets the rFLAGS.CF to 0 if
instruction changed the RMP entry and to 1 if the instruction did not
change the RMP entry. The rFlags.CF will be 1 only when a memory region
is already validated. We should not double validate a memory
as it could lead to a security compromise. If double validation is
detected, terminate the boot.

Cc: James Bottomley <jejb@linux.ibm.com>
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: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 OvmfPkg/Include/Library/MemEncryptSevLib.h                            |  15 ++
 OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/SnpPageStateChange.c        |  17 ++
 OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf          |   4 +
 OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c    |  20 ++
 OvmfPkg/Library/BaseMemEncryptSevLib/SnpPageStateChange.h             |  37 +++
 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c    |  23 ++
 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c | 254 ++++++++++++++++++++
 7 files changed, 370 insertions(+)

diff --git a/OvmfPkg/Include/Library/MemEncryptSevLib.h b/OvmfPkg/Include/Library/MemEncryptSevLib.h
index 03d9eda392..47d6802b61 100644
--- a/OvmfPkg/Include/Library/MemEncryptSevLib.h
+++ b/OvmfPkg/Include/Library/MemEncryptSevLib.h
@@ -215,4 +215,19 @@ MemEncryptSevGetAddressRangeState (
   IN UINTN                    Length
   );
 
+/**
+  If SEV-SNP is active then set the page state of the specified virtual
+  address range. This should be called in SEC and PEI phases only.
+
+  @param[in]  BaseAddress             Base address
+  @param[in]  NumPages                Number of pages starting from the base address
+
+**/
+VOID
+EFIAPI
+MemEncryptSevSnpValidateSystemRam (
+  IN PHYSICAL_ADDRESS                   BaseAddress,
+  IN UINTN                              NumPages
+  );
+
 #endif // _MEM_ENCRYPT_SEV_LIB_H_
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/SnpPageStateChange.c b/OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/SnpPageStateChange.c
new file mode 100644
index 0000000000..dace5c0bcf
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/SnpPageStateChange.c
@@ -0,0 +1,17 @@
+#include <Uefi/UefiBaseType.h>
+
+#include "../SnpPageStateChange.h"
+
+/**
+ The function is used to set the page state when SEV-SNP is active. The page state
+ transition consist of changing the page ownership in the RMP table, and using the
+ PVALIDATE instruction to update the Validated bit in RMP table.
+
+ */
+VOID
+SevSnpValidateSystemRamInternal (
+  IN EFI_PHYSICAL_ADDRESS             BaseAddress,
+  IN UINTN                            NumPages
+  )
+{
+}
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
index 279c38bfbc..8595e244c2 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
@@ -31,15 +31,19 @@
 
 [Sources]
   SecMemEncryptSevLibInternal.c
+  SnpPageStateChange.h
 
 [Sources.X64]
   X64/MemEncryptSevLib.c
   X64/SecVirtualMemory.c
+  X64/SecSnpSystemRamValidate.c
+  X64/SnpPageStateChangeInternal.c
   X64/VirtualMemory.c
   X64/VirtualMemory.h
 
 [Sources.IA32]
   Ia32/MemEncryptSevLib.c
+  Ia32/SnpPageStateChange.c
 
 [LibraryClasses]
   BaseLib
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c
index 69852779e2..35a222e75e 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c
@@ -17,6 +17,8 @@
 #include <Register/Cpuid.h>
 #include <Uefi/UefiBaseType.h>
 
+#include "SnpPageStateChange.h"
+
 /**
   Reads and sets the status of SEV features.
 
@@ -172,3 +174,21 @@ MemEncryptSevLocateInitialSmramSaveStateMapPages (
 {
   return RETURN_UNSUPPORTED;
 }
+
+/**
+  If SEV-SNP is active then set the page state of the specified virtual
+  address range. This should be called in SEC and PEI phases only.
+
+  @param[in]  BaseAddress             Base address
+  @param[in]  NumPages                Number of pages starting from the base address
+
+**/
+VOID
+EFIAPI
+MemEncryptSevSnpValidateSystemRam (
+  IN PHYSICAL_ADDRESS                   BaseAddress,
+  IN UINTN                              NumPages
+  )
+{
+  SevSnpValidateSystemRam (BaseAddress, NumPages);
+}
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/SnpPageStateChange.h b/OvmfPkg/Library/BaseMemEncryptSevLib/SnpPageStateChange.h
new file mode 100644
index 0000000000..3040930999
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/SnpPageStateChange.h
@@ -0,0 +1,37 @@
+/** @file
+
+  SEV-SNP Page Validation functions.
+
+  Copyright (c) 2020 - 2021, AMD Incorporated. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef SNP_PAGE_STATE_INTERNAL_H_
+#define SNP_PAGE_STATE_INTERNAL_H_
+
+//
+// SEV-SNP Page states
+//
+typedef enum {
+  SevSnpPagePrivate,
+  SevSnpPageShared,
+
+} SEV_SNP_PAGE_STATE;
+
+VOID
+SevSnpValidateSystemRam (
+  IN EFI_PHYSICAL_ADDRESS             BaseAddress,
+  IN UINTN                            NumPages
+  );
+
+VOID
+SetPageStateInternal (
+  IN EFI_PHYSICAL_ADDRESS             BaseAddress,
+  IN UINTN                            NumPages,
+  IN SEV_SNP_PAGE_STATE               State,
+  IN BOOLEAN                          UseLargeEntry
+  );
+
+#endif
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c
new file mode 100644
index 0000000000..915706aad0
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c
@@ -0,0 +1,23 @@
+/** @file
+
+  SEV-SNP Page Validation functions.
+
+  Copyright (c) 2020 - 2021, AMD Incorporated. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Uefi/UefiBaseType.h>
+#include <Library/BaseLib.h>
+
+#include "../SnpPageStateChange.h"
+
+VOID
+SevSnpValidateSystemRam (
+  IN EFI_PHYSICAL_ADDRESS             BaseAddress,
+  IN UINTN                            NumPages
+  )
+{
+  SetPageStateInternal (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
+}
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
new file mode 100644
index 0000000000..5a34db33fe
--- /dev/null
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
@@ -0,0 +1,254 @@
+/** @file
+
+  SEV-SNP Page Validation functions.
+
+  Copyright (c) 2020 - 2021, AMD Incorporated. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Uefi/UefiBaseType.h>
+#include <Library/BaseLib.h>
+#include <Library/BaseMemoryLib.h>
+#include <Library/MemEncryptSevLib.h>
+#include <Library/DebugLib.h>
+#include <Library/VmgExitLib.h>
+
+#include <Register/Amd/Ghcb.h>
+#include <Register/Amd/Msr.h>
+
+#include "../SnpPageStateChange.h"
+
+#define IS_ALIGNED(x, y)        ((((x) & (y - 1)) == 0))
+#define PAGES_PER_LARGE_ENTRY   512
+#define EFI_LARGE_PAGE          (EFI_PAGE_SIZE * PAGES_PER_LARGE_ENTRY)
+
+STATIC
+UINTN
+MemoryStateToGhcbOp (
+  IN SEV_SNP_PAGE_STATE   State
+  )
+{
+  UINTN Cmd;
+
+  switch (State) {
+    case SevSnpPageShared: Cmd = SNP_PAGE_STATE_SHARED; break;
+    case SevSnpPagePrivate: Cmd = SNP_PAGE_STATE_PRIVATE; break;
+    default: ASSERT(0);
+  }
+
+  return Cmd;
+}
+
+STATIC
+VOID
+SnpPageStateFailureTerminate (
+  VOID
+  )
+{
+  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 = GHCB_TERMINATE_GHCB_GENERAL;
+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, Msr.GhcbPhysicalAddress);
+
+  AsmVmgExit ();
+
+  ASSERT (FALSE);
+  CpuDeadLoop ();
+}
+
+STATIC
+UINTN
+IssuePvalidate (
+  IN    UINTN       Address,
+  IN    UINTN       RmpPageSize,
+  IN    BOOLEAN     Validate
+  )
+{
+  IA32_EFLAGS32         EFlags;
+  UINTN                 Ret;
+
+  Ret = AsmPvalidate (RmpPageSize, Validate, Address, &EFlags);
+
+  //
+  // Check the rFlags.CF to verify that PVALIDATE updated the RMP
+  // entry. If there was a no change in the RMP entry then we are
+  // either double validating or invalidating the memory. This can
+  // lead to a security compromise.
+  //
+  if (EFlags.Bits.CF) {
+    DEBUG ((DEBUG_ERROR, "%a:%a: Double %a detected for address 0x%Lx\n",
+           gEfiCallerBaseName,
+           __FUNCTION__,
+           Validate ? "Validate" : "Invalidate",
+           Address));
+    SnpPageStateFailureTerminate ();
+  }
+
+  return Ret;
+}
+
+/**
+ This function issues the PVALIDATE instruction to validate or invalidate the memory
+ range specified. If PVALIDATE returns size mismatch then it tries validating with
+ smaller page size.
+
+ */
+STATIC
+VOID
+PvalidateRange (
+  IN  SNP_PAGE_STATE_CHANGE_INFO    *Info,
+  IN  UINTN                         StartIndex,
+  IN  UINTN                         EndIndex,
+  IN  BOOLEAN                       Validate
+  )
+{
+  UINTN         Address, RmpPageSize, Ret, i;
+
+  for (; StartIndex < EndIndex; StartIndex++) {
+    Address = Info->Entry[StartIndex].GuestFrameNumber << EFI_PAGE_SHIFT;
+    RmpPageSize = Info->Entry[StartIndex].PageSize;
+
+    Ret = IssuePvalidate (Address, RmpPageSize, Validate);
+
+    //
+    // If we fail to validate due to size mismatch then try with the
+    // smaller page size. This senario will occur if the backing page in
+    // the RMP entry is 4K and we are validating it as a 2MB.
+    //
+    if ((Ret == PVALIDATE_RET_FAIL_SIZEMISMATCH) &&
+        (RmpPageSize == PVALIDATE_PAGE_SIZE_2M)) {
+      for (i = 0; i < PAGES_PER_LARGE_ENTRY; i++) {
+
+        Ret = IssuePvalidate (Address, PVALIDATE_PAGE_SIZE_4K, Validate);
+        if (Ret) {
+          break;
+        }
+
+        Address = Address + EFI_PAGE_SIZE;
+      }
+    }
+
+    if (Ret) {
+    DEBUG ((DEBUG_ERROR, "%a:%a: Failed to %a address 0x%Lx Error code %d\n",
+           gEfiCallerBaseName,
+           __FUNCTION__,
+           Validate ? "Validate" : "Invalidate",
+           Address,
+           Ret));
+      SnpPageStateFailureTerminate ();
+    }
+  }
+}
+
+/**
+ The function is used to set the page state when SEV-SNP is active. The page state
+ transition consist of changing the page ownership in the RMP table, and using the
+ PVALIDATE instruction to update the Validated bit in RMP table.
+
+ When the UseLargeEntry is set to TRUE, then use the large RMP entry.
+ */
+VOID
+SetPageStateInternal (
+  IN EFI_PHYSICAL_ADDRESS             BaseAddress,
+  IN UINTN                            NumPages,
+  IN SEV_SNP_PAGE_STATE               State,
+  IN BOOLEAN                          UseLargeEntry
+  )
+{
+  EFI_STATUS                      Status;
+  GHCB                            *Ghcb;
+  EFI_PHYSICAL_ADDRESS            NextAddress, EndAddress;
+  MSR_SEV_ES_GHCB_REGISTER        Msr;
+  BOOLEAN                         InterruptState;
+  SNP_PAGE_STATE_CHANGE_INFO      *Info;
+  UINTN                           i, RmpPageSize;
+
+  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
+  Ghcb = Msr.Ghcb;
+
+  EndAddress = BaseAddress + EFI_PAGES_TO_SIZE (NumPages);
+
+  DEBUG ((DEBUG_VERBOSE, "%a:%a Address 0x%Lx - 0x%Lx State = %a LargeEntry = %d\n",
+          gEfiCallerBaseName,
+          __FUNCTION__,
+          BaseAddress,
+          EndAddress,
+          State == SevSnpPageShared ? "Shared" : "Private",
+          UseLargeEntry));
+
+  for (; BaseAddress < EndAddress; BaseAddress = NextAddress) {
+
+    //
+    // Initialize the GHCB and setup scratch sw to point to shared buffer.
+    //
+    VmgInit (Ghcb, &InterruptState);
+    Info = (SNP_PAGE_STATE_CHANGE_INFO *) Ghcb->SharedBuffer;
+
+    SetMem (Info, sizeof (*Info), 0);
+
+    //
+    // Build page state change buffer
+    //
+    for (i = 0; (EndAddress > BaseAddress) && i < SNP_PAGE_STATE_MAX_ENTRY;
+          BaseAddress = NextAddress, i++) {
+      //
+      // Is this a 2MB aligned page? Check if we can use the Large RMP entry.
+      //
+      if (UseLargeEntry &&
+          IS_ALIGNED (BaseAddress, EFI_LARGE_PAGE) &&
+          ((EndAddress - BaseAddress) >> EFI_PAGE_SHIFT) >= PAGES_PER_LARGE_ENTRY) {
+        RmpPageSize = PVALIDATE_PAGE_SIZE_2M;
+        NextAddress = BaseAddress + EFI_LARGE_PAGE;
+      } else {
+        RmpPageSize = PVALIDATE_PAGE_SIZE_4K;
+        NextAddress = BaseAddress + EFI_PAGE_SIZE;
+      }
+
+      Info->Entry[i].GuestFrameNumber = BaseAddress >> EFI_PAGE_SHIFT;
+      Info->Entry[i].PageSize = RmpPageSize;
+      Info->Entry[i].Op = MemoryStateToGhcbOp (State);
+      Info->Entry[i].CurrentPage = 0;
+    }
+
+    Info->Header.CurrentEntry = 0;
+    Info->Header.EndEntry = i - 1;
+
+    //
+    // If the request page state change is shared then invalidate the pages before
+    // adding the page in the RMP table.
+    //
+    if (State == SevSnpPageShared) {
+      PvalidateRange (Info, 0, i, FALSE);
+    }
+
+    //
+    // Issue the VMGEXIT and retry if hypervisor failed to process all the entries.
+    //
+    Ghcb->SaveArea.SwScratch = (UINT64) Ghcb->SharedBuffer;
+    VmgSetOffsetValid (Ghcb, GhcbSwScratch);
+    while (Info->Header.CurrentEntry <= Info->Header.EndEntry) {
+      Status = VmgExit (Ghcb, SVM_EXIT_SNP_PAGE_STATE_CHANGE, 0, 0);
+      if (EFI_ERROR (Status)) {
+        SnpPageStateFailureTerminate ();
+      }
+    }
+
+    //
+    // If the request page state change is shared then invalidate the pages before
+    // adding the page in the RMP table.
+    //
+    if (State == SevSnpPagePrivate) {
+      PvalidateRange (Info, 0, i, TRUE);
+    }
+
+    VmgDone (Ghcb, InterruptState);
+  }
+}
-- 
2.17.1