Re: [PATCH v3] EmbeddedPkg/PrePiMemoryAllocationLib: Add check for space on offset allocation

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

On Fri, 23 Sept 2022 at 17:56, Jeff Brasen <jbrasen@nvidia.com> wrote:
>
> Update check for enough space to occur prior to alignment offset.
> This prevents cases where EfiFreeMemoryTop < EfiFreeMemoryBottom.
>
> Signed-off-by: Jeff Brasen <jbrasen@nvidia.com>

Merged as #3396

Thanks,

> ---
>  .../MemoryAllocationLib.c                     | 48 ++++++++-----------
>  1 file changed, 21 insertions(+), 27 deletions(-)
>
> diff --git a/EmbeddedPkg/Library/PrePiMemoryAllocationLib/MemoryAllocationLib.c b/EmbeddedPkg/Library/PrePiMemoryAllocationLib/MemoryAllocationLib.c
> index 2cc2a71121..08a0add340 100644
> --- a/EmbeddedPkg/Library/PrePiMemoryAllocationLib/MemoryAllocationLib.c
> +++ b/EmbeddedPkg/Library/PrePiMemoryAllocationLib/MemoryAllocationLib.c
> @@ -23,41 +23,35 @@ InternalAllocatePages (
>    )
>  {
>    EFI_PEI_HOB_POINTERS  Hob;
> -  EFI_PHYSICAL_ADDRESS  Offset;
> +  EFI_PHYSICAL_ADDRESS  NewTop;
>
>    Hob.Raw = GetHobList ();
>
> -  // Check to see if on 4k boundary
> -  Offset = Hob.HandoffInformationTable->EfiFreeMemoryTop & 0xFFF;
> -  if (Offset != 0) {
> -    // If not aligned, make the allocation aligned.
> -    Hob.HandoffInformationTable->EfiFreeMemoryTop -= Offset;
> -  }
> +  NewTop  = Hob.HandoffInformationTable->EfiFreeMemoryTop & ~(EFI_PHYSICAL_ADDRESS)EFI_PAGE_MASK;
> +  NewTop -= Pages * EFI_PAGE_SIZE;
>
>    //
>    // Verify that there is sufficient memory to satisfy the allocation
>    //
> -  if (Hob.HandoffInformationTable->EfiFreeMemoryTop - ((Pages * EFI_PAGE_SIZE) + sizeof (EFI_HOB_MEMORY_ALLOCATION)) < Hob.HandoffInformationTable->EfiFreeMemoryBottom) {
> -    return 0;
> -  } else {
> -    //
> -    // Update the PHIT to reflect the memory usage
> -    //
> -    Hob.HandoffInformationTable->EfiFreeMemoryTop -= Pages * EFI_PAGE_SIZE;
> -
> -    // This routine used to create a memory allocation HOB a la PEI, but that's not
> -    // necessary for us.
> -
> -    //
> -    // Create a memory allocation HOB.
> -    //
> -    BuildMemoryAllocationHob (
> -      Hob.HandoffInformationTable->EfiFreeMemoryTop,
> -      Pages * EFI_PAGE_SIZE,
> -      MemoryType
> -      );
> -    return (VOID *)(UINTN)Hob.HandoffInformationTable->EfiFreeMemoryTop;
> +  if (NewTop < (Hob.HandoffInformationTable->EfiFreeMemoryBottom + sizeof (EFI_HOB_MEMORY_ALLOCATION))) {
> +    return NULL;
>    }
> +
> +  //
> +  // Update the PHIT to reflect the memory usage
> +  //
> +  Hob.HandoffInformationTable->EfiFreeMemoryTop = NewTop;
> +
> +  //
> +  // Create a memory allocation HOB.
> +  //
> +  BuildMemoryAllocationHob (
> +    Hob.HandoffInformationTable->EfiFreeMemoryTop,
> +    Pages * EFI_PAGE_SIZE,
> +    MemoryType
> +    );
> +
> +  return (VOID *)(UINTN)Hob.HandoffInformationTable->EfiFreeMemoryTop;
>  }
>
>  /**
> --
> 2.25.1
>