[PATCH 1/2] OvmfPkg: disable build-time relocation for DXEFV modules

[Laszlo Ersek <lersek@redhat.com>]

When the GenFv utility from BaseTools composes a firmware volume, it
checks whether modules in the firmware volume are subject to build-time
relocation. The primary indication for relocation is whether the firmware
volume has a nonzero base address, according to the [FD] section(s) in the
FDF file that refer to the firmware volume.

The idea behind build-time relocation is that XIP (execute in place)
modules will not be relocated at boot-time:

- Pre-DXE phase modules generally execute in place.

  (OVMF is no exception, despite the fact that we have writeable memory
  even in SEC: PEI_CORE and PEIMs run in-place from PEIFV, after SEC
  decompresses PEIFV and DXEFV from FVMAIN_COMPACT (flash) to RAM.
  PEI_CORE and the PEIMs are relocated at boot-time only after PlatformPei
  installs the permanent PEI RAM, and the RAM migration occurs.)

- Modules dispatched by the DXE Core are generally relocated at boot-time.
  However, this is not necessarily so, the LMFA (Load Modules at Fixed
  Address) feature apparently allows in-place execution for such modules
  as well, deriving the load address from the containing firmware volume's
  base address at build time.

  (LMFA is controlled by the
  gEfiMdeModulePkgTokenSpaceGuid.PcdLoadModuleAtFixAddressEnable fixed
  PCD, which we leave disabled in OVMF.)

Therefore GenFv relocates even DXE and UEFI driver modules if the
containing firmware volume has a nonzero base address.

In OVMF, this is the case for both PEIV and DXEFV:

> [FD.MEMFD]
> BaseAddress   = $(MEMFD_BASE_ADDRESS)
> Size          = 0xB00000
> ErasePolarity = 1
> BlockSize     = 0x10000
> NumBlocks     = 0xB0
> ...
> 0x020000|0x0E0000
> gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvSize
> FV = PEIFV
>
> 0x100000|0xA00000
> gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvSize
> FV = DXEFV

While the build-time relocation certainly makes sense for PEIFV (see
above), the reasons for which we specify DXEFV under [FD.MEMFD] are
weaker:

- we set the PcdOvmfDxeMemFvBase and PcdOvmfDxeMemFvSize PCDs here,

- and we ascertain that DXEFV, when decompressed by SEC from
  FVMAIN_COMPACT, will fit into the area allotted here, at build time.

In other words, the build-time relocation of the modules in DXEFV is a
waste of resources. But, it gets worse:

Build-time relocation of an executable is only possible if the on-disk and
in-memory layouts are identical, i.e., if the sections of the PE/COFF
image adhere to the same alignment on disk and in memory. Put differently,
the FileAlignment and SectionAlignment headers must be equal.

For boot-time modules that we build as part of edk2, both alignment values
are 0x20 bytes. For runtime modules that we build as part of edk2, both
alignment values are 0x1000 bytes. This is why the DXEFV relocation,
albeit wasteful, is also successful every time.

Unfortunately, if we try to include a PE/COFF binary in DXEFV that
originates from outside of edk2, the DXEFV relocation can fail due to the
binary having unmatched FileAlignment and SectionAlignment headers. This
is precisely the case with the E3522X2.EFI network driver for the e1000
NIC, from Intel's BootUtil / PREBOOT.EXE distribution.

The solution is to use the FvForceRebase=FALSE override under [FV.DXEFV].
This tells GenFv not to perform build-time relocation on the firmware
volume, despite the FV having a nonzero base address. As stated above,
this relocation has always been useless and wasteful in OVMF, because we
never enable LMFA.

(Put differently, E3522X2.EFI could never be loaded from an FV with LMFA
enabled for the platform because E3522X2.EFI has unmatched FileAlignment
and SectionAlignment headers.)

In DXEFV we also have SMM drivers. Those are relocated at boot-time (into
SMRAM) unconditionally, regardless of LMFA; SMRAM is always discovered at
boot-time.

Kudos to Ard and Liming for the PE/COFF sections & relocations
explanation, and for the FvForceRebase=FALSE tip.

I regression-tested this change in the following configurations (all with
normal boot and S3 suspend/resume):

  IA32,     q35,     SMM,     Linux
  IA32X64,  q35,     SMM,     Linux
  IA32X64,  q35,     SMM,     Windows-8.1
  X64,      i440fx,  no-SMM,  Linux

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=613
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=615
Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Suggested-by: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/OvmfPkgIa32.fdf    | 1 +
 OvmfPkg/OvmfPkgIa32X64.fdf | 1 +
 OvmfPkg/OvmfPkgX64.fdf     | 1 +
 3 files changed, 3 insertions(+)

diff --git a/OvmfPkg/OvmfPkgIa32.fdf b/OvmfPkg/OvmfPkgIa32.fdf
index 09c165882c3f..859457e9aae5 100644
--- a/OvmfPkg/OvmfPkgIa32.fdf
+++ b/OvmfPkg/OvmfPkgIa32.fdf
@@ -168,6 +168,7 @@ [FV.PEIFV]
 ################################################################################
 
 [FV.DXEFV]
+FvForceRebase      = FALSE
 FvNameGuid         = 7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1
 BlockSize          = 0x10000
 FvAlignment        = 16
diff --git a/OvmfPkg/OvmfPkgIa32X64.fdf b/OvmfPkg/OvmfPkgIa32X64.fdf
index 5233314139bc..2a0ed8313786 100644
--- a/OvmfPkg/OvmfPkgIa32X64.fdf
+++ b/OvmfPkg/OvmfPkgIa32X64.fdf
@@ -168,6 +168,7 @@ [FV.PEIFV]
 ################################################################################
 
 [FV.DXEFV]
+FvForceRebase      = FALSE
 FvNameGuid         = 7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1
 BlockSize          = 0x10000
 FvAlignment        = 16
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index 36150101e784..ca61fa125795 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -168,6 +168,7 @@ [FV.PEIFV]
 ################################################################################
 
 [FV.DXEFV]
+FvForceRebase      = FALSE
 FvNameGuid         = 7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1
 BlockSize          = 0x10000
 FvAlignment        = 16
-- 
2.13.1.3.g8be5a757fa67