diff mbox series

[v2,06/11] arm: use ktime_read_raw_clock() for random_get_entropy() instead of zero

Message ID 20220410214951.55294-7-Jason@zx2c4.com (mailing list archive)
State Not Applicable
Headers show
Series archs/random: fallback to using ktime_read_raw_clock() if no cycle counter | expand

Commit Message

Jason A. Donenfeld April 10, 2022, 9:49 p.m. UTC 
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 ktime_read_raw_clock() would be preferable,
because that always needs to return _something_, even falling back to
jiffies eventually. It's not as though ktime_read_raw_clock() 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@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/arm/include/asm/timex.h | 1 +
 1 file changed, 1 insertion(+)
diff mbox series

Patch

diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h
index 7c3b3671d6c2..d0b32ce87254 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() ?: ktime_read_raw_clock()))
 
 #endif