From: Benjamin Doron <benjamin.doron@9elements.com>

Presently, `ArchIsRngSupported()` always returns TRUE, per
https://github.com/tianocore/edk2/blob/1eeca0750af5af2f0e78437bf791ac2de74bde74/MdePkg/Library/BaseRngLib/Rand/RdRand.c#L124-L125.
Therefore, `BaseRngLibConstructor()` should continue to assert RDRAND
support.

However, older platforms do not support RDRAND, such as QEMU in some
configurations. Therefore, define an RngLib library class for such
systems, using a new flag. Maintain current behaviour by default.

Note that this is less secure behaviour, and should be avoided in
production.

Cc: Guo Dong <guo.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Sean Rhodes <sean@starlabs.systems>
Cc: James Lu <james.lu@intel.com>
Cc: Gua Guo <gua.guo@intel.com>
Signed-off-by: Benjamin Doron <benjamin.doron@9elements.com>
---
 UefiPayloadPkg/UefiPayloadPkg.dsc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/UefiPayloadPkg/UefiPayloadPkg.dsc b/UefiPayloadPkg/UefiPayloadPkg.dsc
index 9847f189fff5..1e803ba01567 100644
--- a/UefiPayloadPkg/UefiPayloadPkg.dsc
+++ b/UefiPayloadPkg/UefiPayloadPkg.dsc
@@ -130,6 +130,7 @@
   # This is how BaseCpuTimerLib works, and a recommended way to get Frequence, so set the default value as TRUE.
   # Note: for emulation platform such as QEMU, this may not work and should set it as FALSE
   DEFINE CPU_TIMER_LIB_ENABLE  = TRUE
+  DEFINE CPU_RNG_ENABLE        = TRUE

   DEFINE MULTIPLE_DEBUG_PORT_SUPPORT = FALSE

@@ -204,7 +205,11 @@
 !endif
   IntrinsicLib|CryptoPkg/Library/IntrinsicLib/IntrinsicLib.inf
   OpensslLib|CryptoPkg/Library/OpensslLib/OpensslLib.inf
+!if $(CPU_RNG_ENABLE) == TRUE
   RngLib|MdePkg/Library/BaseRngLib/BaseRngLib.inf
+!else
+  RngLib|MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf
+!endif
   HobLib|UefiPayloadPkg/Library/DxeHobLib/DxeHobLib.inf

   #
--
2.39.2