[edk2-devel] [PATCH v2 28/45] MdePkg: Warn if AArch64 RNDR instruction is not supported

["Sami Mujawar" <sami.mujawar@arm.com>]

The BaseRngLib library constructor for AArch64 asserts if the
RNDR instruction is not supported by the CPU. This approach to
warn about the unsupported instruction may be suitable for the
host platform firmware. However, for a guest firmware the only
mechanism to discover the supported RNG interface is by probing
the processor feature registers.
The guest firmware may therefore assume that RNDR instruction
is supported and if the probe fails, fall back to an alternate
RNG source, e.g. Virtio RNG.

Therefore, replace the assert with a warning message to allow
the guest firmware to progress.

Note:
 - If RNDR instruction is not supported, the GetRandomNumberXXX
   functions will return FALSE to indicate that the random number
   generation has failed. It is expected that the calling function
   checks the status and handles this error appropriately.
 - This change should not have any side effect as the behaviour
   will be similar to that of release builds where the asserts
   would be removed.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
---
 MdePkg/Library/BaseRngLib/AArch64/Rndr.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/MdePkg/Library/BaseRngLib/AArch64/Rndr.c b/MdePkg/Library/BaseRngLib/AArch64/Rndr.c
index d39db62153eed415151e7a27a5931231febd20d3..dc41eea8fbfd7d18bca24e2ebe1cdc56b4eb8d81 100644
--- a/MdePkg/Library/BaseRngLib/AArch64/Rndr.c
+++ b/MdePkg/Library/BaseRngLib/AArch64/Rndr.c
@@ -49,10 +49,14 @@ BaseRngLibConstructor (
   // Determine RNDR support by examining bits 63:60 of the ISAR0 register returned by
   // MSR. A non-zero value indicates that the processor supports the RNDR instruction.
   //
-  Isar0 = ArmReadIdIsar0 ();
-  ASSERT ((Isar0 & RNDR_MASK) != 0);
-
+  Isar0          = ArmReadIdIsar0 ();
   mRndrSupported = ((Isar0 & RNDR_MASK) != 0);
+  if (!mRndrSupported) {
+    DEBUG ((
+      DEBUG_WARN,
+      "WARNING: BaseRngLib: RNDR instruction not supported by the processor.\n"
+      ));
+  }
 
   return EFI_SUCCESS;
 }
-- 
'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'



-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#117701): https://edk2.groups.io/g/devel/message/117701
Mute This Topic: https://groups.io/mt/105483444/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-