Re: [RFC PATCH 3/7] MdeModulePkg/Dxe/Page: take MAX_ALLOC_ADDRESS into account

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Mon, 10 Dec 2018 at 15:52, Gao, Liming <liming.gao@intel.com> wrote:
>
> Ard:
>   I prefer to define MAX_ALLOC_ADDRESS together with MAX_ADDRESS in ProcessorBind.h. I don't want to leave the choice to override MAX_ALLOC_ADDRESS definition.
>

Seems reasonable. What should be the value for X64?

> Thanks
> Liming
> > -----Original Message-----
> > From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Ard Biesheuvel
> > Sent: Monday, December 10, 2018 3:23 PM
> > To: Wang, Jian J <jian.j.wang@intel.com>
> > Cc: Andrew Jones <drjones@redhat.com>; Wu, Hao A <hao.a.wu@intel.com>; edk2-devel@lists.01.org; Gao, Liming
> > <liming.gao@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>; Laszlo Ersek <lersek@redhat.com>
> > Subject: Re: [edk2] [RFC PATCH 3/7] MdeModulePkg/Dxe/Page: take MAX_ALLOC_ADDRESS into account
> >
> > On Mon, 10 Dec 2018 at 03:04, Wang, Jian J <jian.j.wang@intel.com> wrote:
> > >
> > > Hi Ard,
> > >
> > > I think MAX_ALLOC_ADDRESS will affect other archs besides ARM. Please do enough
> > > test for them (IA32/X64 for my concern).
> > >
> >
> > For all other architectures, MAX_ADDRESS == MAX_ALLOC_ADDRESS is
> > always true, so these changes only affect AARCH64.
> >
> > > In addition, do you think it's safer to replace MAX_ADDRESS with MAX_ALLOC_ADDRESS
> > > in MemoryAllocationLib like following situation?
> > >
> > > (MdeModulePkg\Library\DxeCoreMemoryAllocationLib\MemoryAllocationLib.c)
> > > VOID *
> > > InternalAllocateCopyPool (
> > >   IN EFI_MEMORY_TYPE  PoolType,
> > >   IN UINTN            AllocationSize,
> > >   IN CONST VOID       *Buffer
> > >   )
> > > {
> > >   VOID  *Memory;
> > >
> > >   ASSERT (Buffer != NULL);
> > >   ASSERT (AllocationSize <= (MAX_ADDRESS - (UINTN) Buffer + 1));
> > >   ...
> >
> > This assert ensures that the copied buffer does not extend across the
> > end of the address space and wraps. This is a separate concern, and is
> > similar to numerous other occurrences of MAX_ADDRESS that maybe we
> > should update as well at some point. However, it does not affect page
> > allocation at all, it only puts an upper bound on the *size* of the
> > allocation. So the changes as they are will be sufficient to ensure
> > that AllocateCopyPool() does not allocate from a region that is not
> > addressable by the CPU.
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