kselftest/arm64: Add hwcap test for RNG

Validate the RNG hwcap and make sure we don't generate a SIGILL reading
RNDR when it is reported.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220913141101.151400-4-broonie@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/abi/hwcap.c

@@ -33,6 +33,11 @@
  */
 typedef void (*sigill_fn)(void);
 
+static void rng_sigill(void)
+{
+	asm volatile("mrs x0, S3_3_C2_C4_0" : : : "x0");
+}
+
 static void sme_sigill(void)
 {
 	/* RDSVL x0, #0 */
@@ -113,6 +118,13 @@ static const struct hwcap_data {
 	sigill_fn sigill_fn;
 	bool sigill_reliable;
 } hwcaps[] = {
+	{
+		.name = "RNG",
+		.at_hwcap = AT_HWCAP2,
+		.hwcap_bit = HWCAP2_RNG,
+		.cpuinfo = "rng",
+		.sigill_fn = rng_sigill,
+	},
 	{
 		.name = "SME",
 		.at_hwcap = AT_HWCAP2,