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

["Jeff Brasen" <jbrasen@nvidia.com>]

I'll post another version to fix the formatting issue in a bit, but before the patch the issue was we applied the alignment offset before we did a space check.

-Jeff


> -----Original Message-----
> From: Ard Biesheuvel <ardb@kernel.org>
> Sent: Wednesday, September 7, 2022 2:34 AM
> To: Jeff Brasen <jbrasen@nvidia.com>
> Cc: devel@edk2.groups.io; quic_llindhol@quicinc.com;
> ardb+tianocore@kernel.org; abner.chang@hpe.com; daniel.schaefer@hpe.com
> Subject: Re: [PATCH] EmbeddedPkg/PrePiMemoryAllocationLib: Add check for
> space on offset allocation
> 
> External email: Use caution opening links or attachments
> 
> 
> On Thu, 30 Jun 2022 at 21:06, Jeff Brasen <jbrasen@nvidia.com> wrote:
> >
> > Update check for enough space to occur prior to alignment offset.
> > This prevents cases where EfiFreeMemoryTop < EfiFreeMemoryBottom.
> >
> 
> So prior to this patch, we would
> - check for enough space
> - apply the alignment
> - potentially exceed the available space due to alignment padding?
> 
> > Signed-off-by: Jeff Brasen <jbrasen@nvidia.com>
> 
> This patch got mangled so I cannot apply it from the list.
> 
> > ---
> >  .../MemoryAllocationLib.c                     | 53 +++++++++++--------
> >  1 file changed, 30 insertions(+), 23 deletions(-)
> >
> > diff --git
> > a/EmbeddedPkg/Library/PrePiMemoryAllocationLib/MemoryAllocationLib.c
> > b/EmbeddedPkg/Library/PrePiMemoryAllocationLib/MemoryAllocationLib.c
> > index 78f8da5e95..1956d644c3 100644
> > ---
> > a/EmbeddedPkg/Library/PrePiMemoryAllocationLib/MemoryAllocationLib.c
> > +++ b/EmbeddedPkg/Library/PrePiMemoryAllocationLib/MemoryAllocationLib
> > +++ .c
> > @@ -38,37 +38,44 @@ AllocatePages (
> >
> >    Hob.Raw = GetHobList ();
> >
> > -  // Check to see if on 4k boundary
> >    Offset = Hob.HandoffInformationTable->EfiFreeMemoryTop & 0xFFF;
> > +  //
> > +  // Verify that there is sufficient memory to satisfy the allocation
> > + and padding prior to updating anything  //  if
> > + ((Hob.HandoffInformationTable->EfiFreeMemoryTop - ((Pages *
> EFI_PAGE_SIZE) + sizeof (EFI_HOB_MEMORY_ALLOCATION)) - Offset) <
> Hob.HandoffInformationTable->EfiFreeMemoryBottom) {
> > +    if (Offset != 0) {
> > +      DEBUG ((DEBUG_ERROR, "Offset applied without enough space\r\n"));
> > +    } else {
> > +      DEBUG ((DEBUG_ERROR, "Out of memory\r\n"));
> > +    }
> > +
> > +    ASSERT (FALSE);
> > +    return 0;
> > +  }
> > +
> > +  // Check to see if on 4k boundary
> >    if (Offset != 0) {
> >      // If not aligned, make the allocation aligned.
> >      Hob.HandoffInformationTable->EfiFreeMemoryTop -= Offset;
> >    }
> >
> >    //
> > -  // Verify that there is sufficient memory to satisfy the allocation
> > +  // Update the PHIT to reflect the memory usage
> >    //
> > -  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,
> > -      EfiBootServicesData
> > -      );
> > -    return (VOID *)(UINTN)Hob.HandoffInformationTable-
> >EfiFreeMemoryTop;
> > -  }
> > +  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,
> > +    EfiBootServicesData
> > +    );
> > +  return (VOID
> > + *)(UINTN)Hob.HandoffInformationTable->EfiFreeMemoryTop;
> >  }
> >
> >  /**
> > --
> > 2.25.1
> >