OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c

/** @file

  SEV-SNP Page Validation functions.

  Copyright (c) 2021 AMD Incorporated. All rights reserved.<BR>

  SPDX-License-Identifier: BSD-2-Clause-Patent

**/

#include <Uefi/UefiBaseType.h>
#include <Library/BaseLib.h>
#include <Library/MemEncryptSevLib.h>

#include "SnpPageStateChange.h"

//
// The variable used for the VMPL check.
//
STATIC UINT8  gVmpl0Data[4096];

/**
 The function checks whether SEV-SNP guest is booted under VMPL0.

 @retval  TRUE      The guest is booted under VMPL0
 @retval  FALSE     The guest is not booted under VMPL0
 **/
STATIC
BOOLEAN
SevSnpIsVmpl0 (
  VOID
  )
{
  UINT64      Rdx;
  EFI_STATUS  Status;

  //
  // There is no straightforward way to query the current VMPL level.
  // The simplest method is to use the RMPADJUST instruction to change
  // a page permission to a VMPL level-1, and if the guest kernel is
  // launched at a level <= 1, then RMPADJUST instruction will return
  // an error.
  //
  Rdx = 1;

  Status = AsmRmpAdjust ((UINT64)gVmpl0Data, 0, Rdx);
  if (EFI_ERROR (Status)) {
    return FALSE;
  }

  return TRUE;
}

/**
  Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.

  @param[in]  BaseAddress             Base address
  @param[in]  NumPages                Number of pages starting from the base address

**/
VOID
EFIAPI
MemEncryptSevSnpPreValidateSystemRam (
  IN PHYSICAL_ADDRESS  BaseAddress,
  IN UINTN             NumPages
  )
{
  if (!MemEncryptSevSnpIsEnabled ()) {
    return;
  }

  //
  // The page state change uses the PVALIDATE instruction. The instruction
  // can be run on VMPL-0 only. If its not VMPL-0 guest then terminate
  // the boot.
  //
  if (!SevSnpIsVmpl0 ()) {
    SnpPageStateFailureTerminate ();
  }

  InternalSetPageState (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
}