MdeModulePkg: Acpi: enforce exclusion between FirmwareCtrl and XFirmwareCtrl

The code in AcpiTableDxe handles the installation of FADT and FACS in both
possible orders. In the [FADT, FACS] installation order, the FACS is at
once linked into the FADT. In the [FACS, FADT] installation order, the
FACS is stashed temporarily, and it is linked into the FADT when the FADT
is installed later.

According to the ACPI specification, *at most one* of FADT.FirmwareCtrl
and FADT.XFirmwareCtrl may be nonzero. The code is aware of this
requirement, and it never sets both of them to nonzero values at once.

However, the code doesn't expect the following:

- The caller first installs the FACS, which is stashed. The address that
  is saved happens to fall below 4GB.

- The caller then installs a FADT, with a zero FirmwareCtrl field, and a
  nonzero (pre-populated) XFirmwareCtrl field.

In this case the code sets FADT.FirmwareCtrl to the less-than-4GB address
of the stashed FACS, and leaves the different nonzero value in
FADT.XFirmwareCtrl. This violates the ACPI specification.

Prevent this by always zeroing the field that we do *not* set.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jiewen Yao <Jiewen.Yao@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16659 6f19259b-4bc3-4df7-8a09-765794883524

0 files changed, 0 insertions, 0 deletions