OvmfPkg/TlsAuthConfigLib: configure trusted CA certs for HTTPS boot

Introduce TlsAuthConfigLib to read the list of trusted CA certificates
from fw_cfg and to store it to EFI_TLS_CA_CERTIFICATE_VARIABLE.

The fw_cfg file is formatted by the "p11-kit" and "update-ca-trust"
utilities on the host side, so that the host settings take effect in guest
HTTPS boot as well. QEMU forwards the file intact to the firmware. The
contents are sanity-checked by NetworkPkg/HttpDxe code that was added in
commit 0fd13678a6.

Link TlsAuthConfigLib via NULL resolution into TlsAuthConfigDxe. This sets
EFI_TLS_CA_CERTIFICATE_VARIABLE in time for both
NetworkPkg/TlsAuthConfigDxe (for possible HII interaction with the user)
and for NetworkPkg/HttpDxe (for the effective TLS configuration).

The file formatted by "p11-kit" can be large. On a RHEL-7 host, the the
Mozilla CA root certificate bundle -- installed with the "ca-certificates"
package -- is processed into a 182KB file. Thus, create
EFI_TLS_CA_CERTIFICATE_VARIABLE as a volatile & boot-time only variable.
Also, in TLS_ENABLE builds, set the cumulative limit for volatile
variables (PcdVariableStoreSize) to 512KB, and the individual limit for
the same (PcdMaxVolatileVariableSize) to 256KB.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Gary Ching-Pang Lin <glin@suse.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Gary Lin <glin@suse.com>
Tested-by: Gary Lin <glin@suse.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

OvmfPkg/Library/TlsAuthConfigLib/TlsAuthConfigLib.inf

@@ -0,0 +1,55 @@
+## @file
+#
+# A hook-in library for NetworkPkg/TlsAuthConfigDxe, in order to set volatile
+# variables related to TLS configuration, before TlsAuthConfigDxe or HttpDxe
+# (which is a UEFI_DRIVER) consume them.
+#
+# Copyright (C) 2013, 2015, 2018, Red Hat, Inc.
+# Copyright (c) 2008 - 2012, Intel Corporation. All rights reserved.<BR>
+#
+# This program and the accompanying materials are licensed and made available
+# under the terms and conditions of the BSD License which accompanies this
+# distribution. The full text of the license may be found at
+# http://opensource.org/licenses/bsd-license.php
+#
+# THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
+# WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+#
+##
+
+[Defines]
+  INF_VERSION                    = 1.26
+  BASE_NAME                      = TlsAuthConfigLib
+  FILE_GUID                      = 660AB627-4C5F-4D42-A3B6-BD021E9028BD
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = TlsAuthConfigLib|DXE_DRIVER
+  CONSTRUCTOR                    = TlsAuthConfigInit
+
+#
+# The following information is for reference only and not required by the build
+# tools.
+#
+#  VALID_ARCHITECTURES           = IA32 X64 ARM AARCH64
+#
+
+[Sources]
+  TlsAuthConfigLib.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  NetworkPkg/NetworkPkg.dec
+  OvmfPkg/OvmfPkg.dec
+
+[LibraryClasses]
+  BaseLib
+  DebugLib
+  MemoryAllocationLib
+  QemuFwCfgLib
+  UefiRuntimeServicesTableLib
+
+[Guids]
+  gEfiTlsCaCertificateGuid ## PRODUCES ## Variable:L"TlsCaCertificate"
+
+[Depex]
+  gEfiVariableWriteArchProtocolGuid