Re: [edk2-devel] [Patch] StandaloneMmPkg: Fixed communicating from TF-A failed issue

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

On Wed, 16 Jun 2021 at 07:30, Omkar Kulkarni <Omkar.Kulkarni@arm.com> wrote:
>
>
> On 6/10/21 6:44 AM, Ming Huang via groups.io wrote:
> > On 6/9/21 3:10 PM, Ard Biesheuvel wrote:
> > > On Tue, 8 Jun 2021 at 16:21, Ming Huang <huangming@linux.alibaba.com>
> > wrote:
> > >>
> > >> TF-A: TrustedFirmware-a
> > >> SPM: Secure Partition Manager(MM)
> > >>
> > >> For AArch64, when SPM enable in TF-A, TF-A may communicate to MM
> > with
> > >> buffer address (PLAT_SPM_BUF_BASE). The address is different from
> > >> PcdMmBufferBase which use in edk2.
> > >
> > > Then why do we have PcdMmBufferBase?
> >
> > ArmPkg use this Pcd for the base address of non-secure communication
> > buffer.
> >
> > >
> > > Is it possible to set PcdMmBufferBase to the correct value?
> >
> > The secure communication may interrupt the non-secure communication. if
> > we use the same address (PcdMmBufferBase and PLAT_SPM_BUF_BASE), the
> > date in communication buffer may be corrupted.
> >
> > Best Regards,
> > Ming
>
> In case where an interrupt handler executing from EL3 makes a call into StandaloneMM, the handler in EL3 makes an spm call into StandaloneMM using PLAT_SPM_BUF_BASE buffer base address. This PLAT_SPM_BUF_BASE is a shared buffer between EL3 and S-EL0. This is where the following check fails and leads to spm call failure. So this change would help resolve this issue.
>

But is it the right fix? Why would EDK2 even be aware of how EL3 and
S-EL0 communicate with each other, and where the buffer is located?


> >
> > >
> > >> Checking address will let TF-A communicate failed to MM. So remove
> > >> below checking code:
> > >> if (NsCommBufferAddr < mNsCommBuffer.PhysicalStart) {
> > >>   return EFI_ACCESS_DENIED;
> > >> }
> > >>
> > >> Signed-off-by: Ming Huang <huangming@linux.alibaba.com>
> > >> ---
> > >>  StandaloneMmPkg/Drivers/StandaloneMmCpu/AArch64/EventHandle.c |
> > 4
> > >> ----
> > >>  1 file changed, 4 deletions(-)
> > >>
> > >> diff --git
> > >> a/StandaloneMmPkg/Drivers/StandaloneMmCpu/AArch64/EventHandle.c
> > >> b/StandaloneMmPkg/Drivers/StandaloneMmCpu/AArch64/EventHandle.c
> > >> index 63fbe26642..fe98d3181d 100644
> > >> ---
> > a/StandaloneMmPkg/Drivers/StandaloneMmCpu/AArch64/EventHandle.c
> > >> +++
> > b/StandaloneMmPkg/Drivers/StandaloneMmCpu/AArch64/EventHandle.c
> > >> @@ -103,10 +103,6 @@ PiMmStandaloneArmTfCpuDriverEntry (
> > >>      return EFI_INVALID_PARAMETER;
> > >>    }
> > >>
> > >> -  if (NsCommBufferAddr < mNsCommBuffer.PhysicalStart) {
> > >> -    return EFI_ACCESS_DENIED;
> > >> -  }
> > >> -
> > >>    if ((NsCommBufferAddr + sizeof (EFI_MM_COMMUNICATE_HEADER)) >=
> > >>        (mNsCommBuffer.PhysicalStart + mNsCommBuffer.PhysicalSize)) {
> > >>      return EFI_INVALID_PARAMETER;
> > >> --
> > >> 2.17.1
> > >>
> >
> >
> > 
> >
>