On 07/08/20 10:10, Guomin Jiang wrote:
> REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1614
>
> To avoid the TOCTOU, enable paging and set Not Present flag so when
> access any code in the flash range, it will trigger #NP exception.
>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Signed-off-by: Guomin Jiang <guomin.jiang@intel.com>
> ---
> UefiCpuPkg/CpuMpPei/CpuMpPei.inf | 3 +++
> UefiCpuPkg/CpuMpPei/CpuPaging.c | 26 ++++++++++++++++++++++++--
> 2 files changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/UefiCpuPkg/CpuMpPei/CpuMpPei.inf b/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
> index f4d11b861f77..7e511325d8b8 100644
> --- a/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
> +++ b/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
> @@ -46,6 +46,9 @@ [LibraryClasses]
> BaseMemoryLib
> CpuLib
>
> +[Guids]
> + gEdkiiMigratedFvInfoGuid ## SOMETIMES_CONSUMES ## HOB
> +
> [Ppis]
> gEfiPeiMpServicesPpiGuid ## PRODUCES
> gEfiSecPlatformInformationPpiGuid ## SOMETIMES_CONSUMES
> diff --git a/UefiCpuPkg/CpuMpPei/CpuPaging.c b/UefiCpuPkg/CpuMpPei/CpuPaging.c
> index 3bf0574b34c6..04a16fb2b620 100644
> --- a/UefiCpuPkg/CpuMpPei/CpuPaging.c
> +++ b/UefiCpuPkg/CpuMpPei/CpuPaging.c
> @@ -12,6 +12,7 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
> #include <Library/MemoryAllocationLib.h>
> #include <Library/CpuLib.h>
> #include <Library/BaseLib.h>
> +#include <Guid/MigratedFvInfo.h>
>
> #include "CpuMpPei.h"
>
> @@ -605,6 +606,8 @@ MemoryDiscoveredPpiNotifyCallback (
> EFI_STATUS Status;
> BOOLEAN InitStackGuard;
> BOOLEAN InterruptState;
> + EDKII_MIGRATED_FV_INFO *MigratedFvInfo;
> + EFI_PEI_HOB_POINTERS Hob;
>
> if (PcdGetBool (PcdMigrateTemporaryRamFirmwareVolumes)) {
> InterruptState = SaveAndDisableInterrupts ();
> @@ -619,9 +622,14 @@ MemoryDiscoveredPpiNotifyCallback (
> // the task switch (for the sake of stack switch).
> //
> InitStackGuard = FALSE;
> - if (IsIa32PaeSupported () && PcdGetBool (PcdCpuStackGuard)) {
> + Hob.Raw = NULL;
> + if (IsIa32PaeSupported ()) {
> + Hob.Raw = GetFirstGuidHob (&gEdkiiMigratedFvInfoGuid);
> + InitStackGuard = PcdGetBool (PcdCpuStackGuard);
> + }
> +
> + if (InitStackGuard || Hob.Raw != NULL) {
> EnablePaging ();
> - InitStackGuard = TRUE;
> }
>
> Status = InitializeCpuMpWorker ((CONST EFI_PEI_SERVICES **)PeiServices);
> @@ -631,6 +639,20 @@ MemoryDiscoveredPpiNotifyCallback (
> SetupStackGuardPage ();
> }
>
> + while (Hob.Raw != NULL) {
> + MigratedFvInfo = GET_GUID_HOB_DATA (Hob);
> +
> + //
> + // Enable #NP exception, so if the code access after disable NEM, it will generate
> + // to avoid potential vulnerability.
> + //
> + ConvertMemoryPageAttributes (MigratedFvInfo->FvOrgBase, MigratedFvInfo->FvLength, 0);
> +
> + Hob.Raw = GET_NEXT_HOB (Hob);
> + Hob.Raw = GetNextGuidHob (&gEdkiiMigratedFvInfoGuid, Hob.Raw);
> + }
> + CpuFlushTlb ();
> +
> return Status;
> }
>
>
Acked-by: Laszlo Ersek <lersek@redhat.com>
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