Re: [PATCH v4 4/5] arm64: Add support for SMCCC TRNG entropy source

On Fri, 11 Dec 2020 16:26:12 +0000
Mark Brown [off-list ref] wrote:

On Fri, Dec 11, 2020 at 04:00:04PM +0000, Andre Przywara wrote:

quoted

 static inline bool __must_check arch_get_random_seed_long(unsigned
long *v) {
+	struct arm_smccc_res res;
+
+	/*
+	 * We prefer the SMCCC call, since its semantics (return
actual
+	 * hardware backed entropy) is closer to the idea behind
this
+	 * function here than what even the RNDRSS register
provides
+	 * (the output of a pseudo RNG freshly seeded by a TRNG).
+	 */  

This logic...

quoted

@@ -77,10 +117,20 @@ arch_get_random_seed_long_early(unsigned long

*v) {
 	WARN_ON(system_state != SYSTEM_BOOTING);
 
-	if (!__early_cpu_has_rndr())
-		return false;
+	if (__early_cpu_has_rndr())
+		return __arm64_rndr(v);
+
+	if (smccc_trng_available) {
+		struct arm_smccc_res res;
 
-	return __arm64_rndr(v);
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64,
&res);
+		if ((int)res.a0 >= 0) {
+			*v = res.a3;
+			return true;
+		}
+	}
+
+	return false;  

...seems to also apply here but we prefer the RNDR instead of the
SMCC. We probably want to either do the same thing or add a comment
saying what's going on.

Argh, you are right, I missed to change this part as well.

Will send a fixed and rebased v5 ASAP.

Cheers,
Andre



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