Re: [edk2-devel] [PATCH v5 08/28] UefiCpuPkg: Always Set Stack Guard in MpPei Init

["Laszlo Ersek" <lersek@redhat.com>]

On 10/9/23 02:07, Taylor Beebe wrote:
> Memory protection is not set in PEI and ingested during and
> after DXE handoff. This paradigm means that the platform cannot
> reliably query the stack guard setting during MpInit. Because the
> execution path of PEI consistent and no third party
> code is executed, setting the stack guard in MpInit on every
> boot should be fine.

I don't understand this commit message at all -- I don't understand any
one of those sentences. Please explain in detail.

This is an intrusive change; it basically forces all platforms that use
CpuMpPei to a mode with PcdCpuStackGuard=TRUE. That may not be
consistent with what a platform wants, plus it seems to invalidate the
definition of PcdCpuStackGuard.

Is the problem that PcdGetBool() does not work? (I'd doubt that;
PcdCpuStackGuard can only be fixed-at-build.)

You could make the argument that PcdCpuStackGuard is *already* mis-used
in CpuMpPei, given that the PCD's definition says

  ## Indicates if UEFI Stack Guard will be enabled.
  #  If enabled, stack overflow in UEFI can be caught, preventing chaotic consequences.<BR><BR>

and "UEFI" is not PEI. But if this is your argument, then that's what
the commit message should state.

Thanks,
Laszlo

>
> Signed-off-by: Taylor Beebe <taylor.d.beebe@gmail.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  UefiCpuPkg/CpuMpPei/CpuMpPei.c   |  8 +++-----
>  UefiCpuPkg/CpuMpPei/CpuPaging.c  | 16 ++++++++--------
>  UefiCpuPkg/CpuMpPei/CpuMpPei.h   |  3 ++-
>  UefiCpuPkg/CpuMpPei/CpuMpPei.inf |  1 -
>  4 files changed, 13 insertions(+), 15 deletions(-)
>
> diff --git a/UefiCpuPkg/CpuMpPei/CpuMpPei.c b/UefiCpuPkg/CpuMpPei/CpuMpPei.c
> index b504bea3cfeb..ca0c6bdb4b21 100644
> --- a/UefiCpuPkg/CpuMpPei/CpuMpPei.c
> +++ b/UefiCpuPkg/CpuMpPei/CpuMpPei.c
> @@ -469,10 +469,6 @@ InitializeMpExceptionStackSwitchHandlers (
>    EFI_STATUS                      Status;
>    UINT8                           *Buffer;
>
> -  if (!PcdGetBool (PcdCpuStackGuard)) {
> -    return;
> -  }
> -
>    Status = MpInitLibGetNumberOfProcessors (&NumberOfProcessors, NULL);
>    ASSERT_EFI_ERROR (Status);
>
> @@ -589,7 +585,9 @@ InitializeCpuMpWorker (
>    //
>    // Special initialization for the sake of Stack Guard
>    //
> -  InitializeMpExceptionStackSwitchHandlers ();
> +  if (mInitStackGuard) {
> +    InitializeMpExceptionStackSwitchHandlers ();
> +  }
>
>    //
>    // Update and publish CPU BIST information
> diff --git a/UefiCpuPkg/CpuMpPei/CpuPaging.c b/UefiCpuPkg/CpuMpPei/CpuPaging.c
> index b7ddb0005b6f..0ab8ceeee8a6 100644
> --- a/UefiCpuPkg/CpuMpPei/CpuPaging.c
> +++ b/UefiCpuPkg/CpuMpPei/CpuPaging.c
> @@ -68,6 +68,8 @@ EFI_PEI_NOTIFY_DESCRIPTOR  mPostMemNotifyList[] = {
>    }
>  };
>
> +BOOLEAN  mInitStackGuard = FALSE;
> +
>  /**
>    The function will check if IA32 PAE is supported.
>
> @@ -532,7 +534,7 @@ SetupStackGuardPage (
>  }
>
>  /**
> -  Enable/setup stack guard for each processor if PcdCpuStackGuard is set to TRUE.
> +  Enable/setup stack guard for each processor.
>
>    Doing this in the memory-discovered callback is to make sure the Stack Guard
>    feature to cover as most PEI code as possible.
> @@ -553,7 +555,6 @@ MemoryDiscoveredPpiNotifyCallback (
>    )
>  {
>    EFI_STATUS              Status;
> -  BOOLEAN                 InitStackGuard;
>    EDKII_MIGRATED_FV_INFO  *MigratedFvInfo;
>    EFI_PEI_HOB_POINTERS    Hob;
>    IA32_CR0                Cr0;
> @@ -563,11 +564,10 @@ MemoryDiscoveredPpiNotifyCallback (
>    // initialization later will not contain paging information and then fail
>    // the task switch (for the sake of stack switch).
>    //
> -  InitStackGuard = FALSE;
> -  Hob.Raw        = NULL;
> +  Hob.Raw = NULL;
>    if (IsIa32PaeSupported ()) {
> -    Hob.Raw        = GetFirstGuidHob (&gEdkiiMigratedFvInfoGuid);
> -    InitStackGuard = PcdGetBool (PcdCpuStackGuard);
> +    Hob.Raw         = GetFirstGuidHob (&gEdkiiMigratedFvInfoGuid);
> +    mInitStackGuard = TRUE;
>    }
>
>    //
> @@ -575,7 +575,7 @@ MemoryDiscoveredPpiNotifyCallback (
>    // is to enable paging if it is not enabled (only in 32bit mode).
>    //
>    Cr0.UintN = AsmReadCr0 ();
> -  if ((Cr0.Bits.PG == 0) && (InitStackGuard || (Hob.Raw != NULL))) {
> +  if ((Cr0.Bits.PG == 0) && (mInitStackGuard || (Hob.Raw != NULL))) {
>      ASSERT (sizeof (UINTN) == sizeof (UINT32));
>
>      Status = EnablePaePageTable ();
> @@ -588,7 +588,7 @@ MemoryDiscoveredPpiNotifyCallback (
>    Status = InitializeCpuMpWorker ((CONST EFI_PEI_SERVICES **)PeiServices);
>    ASSERT_EFI_ERROR (Status);
>
> -  if (InitStackGuard) {
> +  if (mInitStackGuard) {
>      SetupStackGuardPage ();
>    }
>
> diff --git a/UefiCpuPkg/CpuMpPei/CpuMpPei.h b/UefiCpuPkg/CpuMpPei/CpuMpPei.h
> index 1b9a94e18fdf..d0db4e480e13 100644
> --- a/UefiCpuPkg/CpuMpPei/CpuMpPei.h
> +++ b/UefiCpuPkg/CpuMpPei/CpuMpPei.h
> @@ -31,6 +31,7 @@
>  #include <Library/CpuPageTableLib.h>
>
>  extern EFI_PEI_PPI_DESCRIPTOR  mPeiCpuMpPpiDesc;
> +extern BOOLEAN                 mInitStackGuard;
>
>  /**
>    This service retrieves the number of logical processor in the platform
> @@ -426,7 +427,7 @@ InitializeCpuMpWorker (
>    );
>
>  /**
> -  Enable/setup stack guard for each processor if PcdCpuStackGuard is set to TRUE.
> +  Enable/setup stack guard for each processor.
>
>    Doing this in the memory-discovered callback is to make sure the Stack Guard
>    feature to cover as most PEI code as possible.
> diff --git a/UefiCpuPkg/CpuMpPei/CpuMpPei.inf b/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
> index 865be5627e85..6a987754120a 100644
> --- a/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
> +++ b/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
> @@ -64,7 +64,6 @@ [Ppis]
>
>  [Pcd]
>    gEfiMdeModulePkgTokenSpaceGuid.PcdPteMemoryEncryptionAddressOrMask    ## CONSUMES
> -  gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard                       ## CONSUMES
>    gUefiCpuPkgTokenSpaceGuid.PcdCpuStackSwitchExceptionList              ## SOMETIMES_CONSUMES
>    gUefiCpuPkgTokenSpaceGuid.PcdCpuKnownGoodStackSize                    ## SOMETIMES_CONSUMES
>    gUefiCpuPkgTokenSpaceGuid.PcdCpuApStackSize                           ## SOMETIMES_CONSUMES



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