OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c

   1 /** @file
   2
   3   SEV-SNP Page Validation functions.
   4
   5   Copyright (c) 2021 AMD Incorporated. All rights reserved.<BR>
   6
   7   SPDX-License-Identifier: BSD-2-Clause-Patent
   8
   9 **/
  10
  11 #include <Uefi/UefiBaseType.h>
  12 #include <Library/BaseLib.h>
  13 #include <Library/MemEncryptSevLib.h>
  14
  15 #include "SnpPageStateChange.h"
  16
  17 //
  18 // The variable used for the VMPL check.
  19 //
  20 STATIC UINT8  gVmpl0Data[4096];
  21
  22 /**
  23  The function checks whether SEV-SNP guest is booted under VMPL0.
  24
  25  @retval  TRUE      The guest is booted under VMPL0
  26  @retval  FALSE     The guest is not booted under VMPL0
  27  **/
  28 STATIC
  29 BOOLEAN
  30 SevSnpIsVmpl0 (
  31   VOID
  32   )
  33 {
  34   UINT64      Rdx;
  35   EFI_STATUS  Status;
  36
  37   //
  38   // There is no straightforward way to query the current VMPL level.
  39   // The simplest method is to use the RMPADJUST instruction to change
  40   // a page permission to a VMPL level-1, and if the guest kernel is
  41   // launched at a level <= 1, then RMPADJUST instruction will return
  42   // an error.
  43   //
  44   Rdx = 1;
  45
  46   Status = AsmRmpAdjust ((UINT64)gVmpl0Data, 0, Rdx);
  47   if (EFI_ERROR (Status)) {
  48     return FALSE;
  49   }
  50
  51   return TRUE;
  52 }
  53
  54 /**
  55   Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.
  56
  57   @param[in]  BaseAddress             Base address
  58   @param[in]  NumPages                Number of pages starting from the base address
  59
  60 **/
  61 VOID
  62 EFIAPI
  63 MemEncryptSevSnpPreValidateSystemRam (
  64   IN PHYSICAL_ADDRESS  BaseAddress,
  65   IN UINTN             NumPages
  66   )
  67 {
  68   if (!MemEncryptSevSnpIsEnabled ()) {
  69     return;
  70   }
  71
  72   //
  73   // The page state change uses the PVALIDATE instruction. The instruction
  74   // can be run on VMPL-0 only. If its not VMPL-0 guest then terminate
  75   // the boot.
  76   //
  77   if (!SevSnpIsVmpl0 ()) {
  78     SnpPageStateFailureTerminate ();
  79   }
  80
  81   InternalSetPageState (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
  82 }