Re: [edk2-devel] [PATCH 4/4] ArmPkg/CpuDxe: Implement EFI memory attributes protocol

["Ard Biesheuvel" <ardb@kernel.org>]

On Wed, 1 Feb 2023 at 19:41, Taylor Beebe <t@taylorbeebe.com> wrote:
>
> Hey Ard,
>
> Have you encountered complications which stem from the lack of
> pre-allocated page table memory on ARM devices utilizing the memory
> protection policy?
>

Interesting. No I haven't, but I agree it is a potential concern.

> My observation is the call stack can end up something like:
>
> 1. MemoryAttributeProtocol->SetMemoryAttributes(EFI_MEMORY_RO)
> 2. ArmSetMemoryRegionReadOnly ()
> 3. SetMemoryRegionAttribute()
> 4. UpdateRegionMapping()
> 5. UpdateRegionMappingRecursive()
> 6. AllocatePages() -> Need memory for a translation table entry
> 7. CoreAllocatePages()
> 8. ApplyMemoryProtectionPolicy() -> Policy says new page should be XN
> 9. gCpu->SetMemoryAttributes()
> 10. Back to 3 and loop infinitely
>

So one thing that makes this scenario unlikely (I think) is that by
default, all unallocated space has the XP attribute set already, and
so allocating a page table with XP attributes should not result in the
need for a block entry split, and therefore no allocation for a next
level table. Perhaps we need some asserts to diagnose this at runtime?

> On 1/31/2023 2:35 PM, Ard Biesheuvel wrote:
> > Expose the protocol introduced in v2.10 that permits the caller to
> > manage mapping permissions in the page tables.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >   ArmPkg/Drivers/CpuDxe/CpuDxe.c          |   2 +
> >   ArmPkg/Drivers/CpuDxe/CpuDxe.h          |   3 +
> >   ArmPkg/Drivers/CpuDxe/CpuDxe.inf        |   2 +
> >   ArmPkg/Drivers/CpuDxe/MemoryAttribute.c | 242 ++++++++++++++++++++
> >   4 files changed, 249 insertions(+)
> >
> > diff --git a/ArmPkg/Drivers/CpuDxe/CpuDxe.c b/ArmPkg/Drivers/CpuDxe/CpuDxe.c
> > index e6742f0a25fc..d04958e79e52 100644
> > --- a/ArmPkg/Drivers/CpuDxe/CpuDxe.c
> > +++ b/ArmPkg/Drivers/CpuDxe/CpuDxe.c
> > @@ -244,6 +244,8 @@ CpuDxeInitialize (
> >                     &mCpuHandle,
> >
> >                     &gEfiCpuArchProtocolGuid,
> >
> >                     &mCpu,
> >
> > +                  &gEfiMemoryAttributeProtocolGuid,
> >
> > +                  &mMemoryAttribute,
> >
> >                     NULL
> >
> >                     );
> >
> >
> >
> > diff --git a/ArmPkg/Drivers/CpuDxe/CpuDxe.h b/ArmPkg/Drivers/CpuDxe/CpuDxe.h
> > index 8933fa90c4ed..f45d2bc101a3 100644
> > --- a/ArmPkg/Drivers/CpuDxe/CpuDxe.h
> > +++ b/ArmPkg/Drivers/CpuDxe/CpuDxe.h
> > @@ -30,9 +30,12 @@
> >   #include <Protocol/Cpu.h>
> >
> >   #include <Protocol/DebugSupport.h>
> >
> >   #include <Protocol/LoadedImage.h>
> >
> > +#include <Protocol/MemoryAttribute.h>
> >
> >
> >
> >   extern BOOLEAN  mIsFlushingGCD;
> >
> >
> >
> > +extern EFI_MEMORY_ATTRIBUTE_PROTOCOL  mMemoryAttribute;
> >
> > +
> >
> >   /**
> >
> >     This function registers and enables the handler specified by InterruptHandler for a processor
> >
> >     interrupt or exception type specified by InterruptType. If InterruptHandler is NULL, then the
> >
> > diff --git a/ArmPkg/Drivers/CpuDxe/CpuDxe.inf b/ArmPkg/Drivers/CpuDxe/CpuDxe.inf
> > index 10792b393fc8..e732e21cb94a 100644
> > --- a/ArmPkg/Drivers/CpuDxe/CpuDxe.inf
> > +++ b/ArmPkg/Drivers/CpuDxe/CpuDxe.inf
> > @@ -23,6 +23,7 @@ [Sources.Common]
> >     CpuDxe.h
> >
> >     CpuMmuCommon.c
> >
> >     Exception.c
> >
> > +  MemoryAttribute.c
> >
> >
> >
> >   [Sources.ARM]
> >
> >     Arm/Mmu.c
> >
> > @@ -53,6 +54,7 @@ [LibraryClasses]
> >
> >
> >   [Protocols]
> >
> >     gEfiCpuArchProtocolGuid
> >
> > +  gEfiMemoryAttributeProtocolGuid
> >
> >
> >
> >   [Guids]
> >
> >     gEfiDebugImageInfoTableGuid
> >
> > diff --git a/ArmPkg/Drivers/CpuDxe/MemoryAttribute.c b/ArmPkg/Drivers/CpuDxe/MemoryAttribute.c
> > new file mode 100644
> > index 000000000000..9aeb83fff1b9
> > --- /dev/null
> > +++ b/ArmPkg/Drivers/CpuDxe/MemoryAttribute.c
> > @@ -0,0 +1,242 @@
> > +/** @file
> >
> > +
> >
> > +  Copyright (c) 2023, Google LLC. All rights reserved.
> >
> > +
> >
> > +  SPDX-License-Identifier: BSD-2-Clause-Patent
> >
> > +
> >
> > +**/
> >
> > +
> >
> > +#include "CpuDxe.h"
> >
> > +
> >
> > +/**
> >
> > +  This function retrieves the attributes of the memory region specified by
> >
> > +  BaseAddress and Length. If different attributes are got from different part
> >
> > +  of the memory region, EFI_NO_MAPPING will be returned.
> >
> > +
> >
> > +  @param  This              The EFI_MEMORY_ATTRIBUTE_PROTOCOL instance.
> >
> > +  @param  BaseAddress       The physical address that is the start address of
> >
> > +                            a memory region.
> >
> > +  @param  Length            The size in bytes of the memory region.
> >
> > +  @param  Attributes        Pointer to attributes returned.
> >
> > +
> >
> > +  @retval EFI_SUCCESS           The attributes got for the memory region.
> >
> > +  @retval EFI_INVALID_PARAMETER Length is zero.
> >
> > +                                Attributes is NULL.
> >
> > +  @retval EFI_NO_MAPPING        Attributes are not consistent cross the memory
> >
> > +                                region.
> >
> > +  @retval EFI_UNSUPPORTED       The processor does not support one or more
> >
> > +                                bytes of the memory resource range specified
> >
> > +                                by BaseAddress and Length.
> >
> > +
> >
> > +**/
> >
> > +STATIC
> >
> > +EFI_STATUS
> >
> > +GetMemoryAttributes (
> >
> > +  IN  EFI_MEMORY_ATTRIBUTE_PROTOCOL       *This,
> >
> > +  IN  EFI_PHYSICAL_ADDRESS                BaseAddress,
> >
> > +  IN  UINT64                              Length,
> >
> > +  OUT UINT64                              *Attributes
> >
> > +  )
> >
> > +{
> >
> > +  UINTN       RegionAddress;
> >
> > +  UINTN       RegionLength;
> >
> > +  UINTN       RegionAttributes;
> >
> > +  UINTN       Union;
> >
> > +  UINTN       Intersection;
> >
> > +  EFI_STATUS  Status;
> >
> > +
> >
> > +  if ((Length == 0) || (Attributes == NULL)) {
> >
> > +    return EFI_INVALID_PARAMETER;
> >
> > +  }
> >
> > +
> >
> > +  DEBUG ((DEBUG_INFO,
> >
> > +          "%a: BaseAddress == 0x%lx, Length == 0x%lx\n",
> >
> > +          __FUNCTION__,
> >
> > +          (UINTN)BaseAddress,
> >
> > +          (UINTN)Length
> >
> > +          ));
> >
> > +
> >
> > +  Union         = 0;
> >
> > +  Intersection  = MAX_UINTN;
> >
> > +
> >
> > +  for (RegionAddress = (UINTN)BaseAddress;
> >
> > +       RegionAddress < (UINTN)(BaseAddress + Length);
> >
> > +       RegionAddress += RegionLength) {
> >
> > +
> >
> > +    Status = GetMemoryRegion (&RegionAddress,
> >
> > +                              &RegionLength,
> >
> > +                              &RegionAttributes
> >
> > +                              );
> >
> > +
> >
> > +    DEBUG ((DEBUG_INFO,
> >
> > +            "%a: RegionAddress == 0x%lx, RegionLength == 0x%lx, RegionAttributes == 0x%lx\n",
> >
> > +            __FUNCTION__,
> >
> > +            RegionAddress,
> >
> > +            RegionLength,
> >
> > +            RegionAttributes
> >
> > +            ));
> >
> > +
> >
> > +    if (EFI_ERROR (Status)) {
> >
> > +      return EFI_NO_MAPPING;
> >
> > +    }
> >
> > +
> >
> > +    Union         |= RegionAttributes;
> >
> > +    Intersection  &= RegionAttributes;
> >
> > +  }
> >
> > +
> >
> > +  DEBUG ((DEBUG_INFO,
> >
> > +          "%a: Union == %lx, Intersection == %lx\n",
> >
> > +          __FUNCTION__,
> >
> > +          Union,
> >
> > +          Intersection
> >
> > +          ));
> >
> > +
> >
> > +  if (Union != Intersection) {
> >
> > +    return EFI_NO_MAPPING;
> >
> > +  }
> >
> > +
> >
> > +  *Attributes = PageAttributeToGcdAttribute (Union) & (EFI_MEMORY_RO | EFI_MEMORY_XP);
> >
> > +  return EFI_SUCCESS;
> >
> > +}
> >
> > +
> >
> > +/**
> >
> > +  This function set given attributes of the memory region specified by
> >
> > +  BaseAddress and Length.
> >
> > +
> >
> > +  The valid Attributes is EFI_MEMORY_RP, EFI_MEMORY_XP, and EFI_MEMORY_RO.
> >
> > +
> >
> > +  @param  This              The EFI_MEMORY_ATTRIBUTE_PROTOCOL instance.
> >
> > +  @param  BaseAddress       The physical address that is the start address of
> >
> > +                            a memory region.
> >
> > +  @param  Length            The size in bytes of the memory region.
> >
> > +  @param  Attributes        The bit mask of attributes to set for the memory
> >
> > +                            region.
> >
> > +
> >
> > +  @retval EFI_SUCCESS           The attributes were set for the memory region.
> >
> > +  @retval EFI_INVALID_PARAMETER Length is zero.
> >
> > +                                Attributes specified an illegal combination of
> >
> > +                                attributes that cannot be set together.
> >
> > +  @retval EFI_UNSUPPORTED       The processor does not support one or more
> >
> > +                                bytes of the memory resource range specified
> >
> > +                                by BaseAddress and Length.
> >
> > +                                The bit mask of attributes is not supported for
> >
> > +                                the memory resource range specified by
> >
> > +                                BaseAddress and Length.
> >
> > +
> >
> > +**/
> >
> > +STATIC
> >
> > +EFI_STATUS
> >
> > +SetMemoryAttributes (
> >
> > +  IN  EFI_MEMORY_ATTRIBUTE_PROTOCOL       *This,
> >
> > +  IN  EFI_PHYSICAL_ADDRESS                BaseAddress,
> >
> > +  IN  UINT64                              Length,
> >
> > +  IN  UINT64                              Attributes
> >
> > +  )
> >
> > +{
> >
> > +  EFI_STATUS  Status;
> >
> > +
> >
> > +  DEBUG ((DEBUG_INFO,
> >
> > +          "%a: BaseAddress == 0x%lx, Length == 0x%lx, Attributes == 0x%lx\n",
> >
> > +          __FUNCTION__,
> >
> > +          (UINTN)BaseAddress,
> >
> > +          (UINTN)Length,
> >
> > +          (UINTN)Attributes
> >
> > +          ));
> >
> > +
> >
> > +  if ((Length == 0) ||
> >
> > +      ((Attributes & ~(EFI_MEMORY_RO | EFI_MEMORY_RP | EFI_MEMORY_XP)) != 0)) {
> >
> > +    return EFI_INVALID_PARAMETER;
> >
> > +  }
> >
> > +
> >
> > +  if ((Attributes & EFI_MEMORY_RP) != 0) {
> >
> > +    return EFI_UNSUPPORTED;
> >
> > +  }
> >
> > +
> >
> > +  if ((Attributes & EFI_MEMORY_RO) != 0) {
> >
> > +    Status = ArmSetMemoryRegionReadOnly (BaseAddress, Length);
> >
> > +    if (EFI_ERROR (Status)) {
> >
> > +      return EFI_UNSUPPORTED;
> >
> > +    }
> >
> > +  }
> >
> > +
> >
> > +  if ((Attributes & EFI_MEMORY_XP) != 0) {
> >
> > +    Status = ArmSetMemoryRegionNoExec (BaseAddress, Length);
> >
> > +    if (EFI_ERROR (Status)) {
> >
> > +      return EFI_UNSUPPORTED;
> >
> > +    }
> >
> > +  }
> >
> > +
> >
> > +  return EFI_SUCCESS;
> >
> > +}
> >
> > +
> >
> > +/**
> >
> > +  This function clears given attributes of the memory region specified by
> >
> > +  BaseAddress and Length.
> >
> > +
> >
> > +  The valid Attributes is EFI_MEMORY_RP, EFI_MEMORY_XP, and EFI_MEMORY_RO.
> >
> > +
> >
> > +  @param  This              The EFI_MEMORY_ATTRIBUTE_PROTOCOL instance.
> >
> > +  @param  BaseAddress       The physical address that is the start address of
> >
> > +                            a memory region.
> >
> > +  @param  Length            The size in bytes of the memory region.
> >
> > +  @param  Attributes        The bit mask of attributes to clear for the memory
> >
> > +                            region.
> >
> > +
> >
> > +  @retval EFI_SUCCESS           The attributes were cleared for the memory region.
> >
> > +  @retval EFI_INVALID_PARAMETER Length is zero.
> >
> > +                                Attributes specified an illegal combination of
> >
> > +                                attributes that cannot be cleared together.
> >
> > +  @retval EFI_UNSUPPORTED       The processor does not support one or more
> >
> > +                                bytes of the memory resource range specified
> >
> > +                                by BaseAddress and Length.
> >
> > +                                The bit mask of attributes is not supported for
> >
> > +                                the memory resource range specified by
> >
> > +                                BaseAddress and Length.
> >
> > +
> >
> > +**/
> >
> > +STATIC
> >
> > +EFI_STATUS
> >
> > +ClearMemoryAttributes (
> >
> > +  IN  EFI_MEMORY_ATTRIBUTE_PROTOCOL       *This,
> >
> > +  IN  EFI_PHYSICAL_ADDRESS                BaseAddress,
> >
> > +  IN  UINT64                              Length,
> >
> > +  IN  UINT64                              Attributes
> >
> > +  )
> >
> > +{
> >
> > +  EFI_STATUS  Status;
> >
> > +
> >
> > +  DEBUG ((DEBUG_INFO,
> >
> > +          "%a: BaseAddress == 0x%lx, Length == 0x%lx, Attributes == 0x%lx\n",
> >
> > +          __FUNCTION__,
> >
> > +          (UINTN)BaseAddress,
> >
> > +          (UINTN)Length,
> >
> > +          (UINTN)Attributes
> >
> > +          ));
> >
> > +
> >
> > +  if ((Length == 0) ||
> >
> > +      ((Attributes & ~(EFI_MEMORY_RO | EFI_MEMORY_RP | EFI_MEMORY_XP)) != 0)) {
> >
> > +    return EFI_INVALID_PARAMETER;
> >
> > +  }
> >
> > +
> >
> > +  if ((Attributes & EFI_MEMORY_RO) != 0) {
> >
> > +    Status = ArmClearMemoryRegionReadOnly (BaseAddress, Length);
> >
> > +    if (EFI_ERROR (Status)) {
> >
> > +      return EFI_UNSUPPORTED;
> >
> > +    }
> >
> > +  }
> >
> > +
> >
> > +  if ((Attributes & EFI_MEMORY_XP) != 0) {
> >
> > +    Status = ArmClearMemoryRegionNoExec (BaseAddress, Length);
> >
> > +    if (EFI_ERROR (Status)) {
> >
> > +      return EFI_UNSUPPORTED;
> >
> > +    }
> >
> > +  }
> >
> > +
> >
> > +  return EFI_SUCCESS;
> >
> > +}
> >
> > +
> >
> > +EFI_MEMORY_ATTRIBUTE_PROTOCOL  mMemoryAttribute = {
> >
> > +  GetMemoryAttributes,
> >
> > +  SetMemoryAttributes,
> >
> > +  ClearMemoryAttributes
> >
> > +};
> >
>
> --
> Taylor Beebe
> Software Engineer @ Microsoft
>
>
> 
>
>