[PATCH v5 05/11] arm: use fallback for random_get_entropy() instead of zero
Jason A. Donenfeld
Jason at zx2c4.com
Tue Apr 19 04:16:44 PDT 2022
In the event that random_get_entropy() can't access a cycle counter or
similar, falling back to returning 0 is really not the best we can do.
Instead, at least calling random_get_entropy_fallback() would be
preferable, because that always needs to return _something_, even
falling back to jiffies eventually. It's not as though
random_get_entropy_fallback() is super high precision or guaranteed to
be entropic, but basically anything that's not zero all the time is
better than returning zero all the time.
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Arnd Bergmann <arnd at arndb.de>
Cc: Russell King <linux at armlinux.org.uk>
Signed-off-by: Jason A. Donenfeld <Jason at zx2c4.com>
---
arch/arm/include/asm/timex.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h
index 7c3b3671d6c2..6d1337c169cd 100644
--- a/arch/arm/include/asm/timex.h
+++ b/arch/arm/include/asm/timex.h
@@ -11,5 +11,6 @@
typedef unsigned long cycles_t;
#define get_cycles() ({ cycles_t c; read_current_timer(&c) ? 0 : c; })
+#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback())
#endif
--
2.35.1
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