diff mbox series

[RFC,v1,03/10] riscv: use sched_clock() for random_get_entropy() instead of zero

Message ID 20220408182145.142506-4-Jason@zx2c4.com (mailing list archive)
State New, archived
Headers show
Series archs/random: fallback to using sched_clock() if no cycle counter | expand

Commit Message

Jason A. Donenfeld April 8, 2022, 6:21 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 sched_clock() would be preferable, because
that always needs to return _something_, even falling back to jiffies
eventually. It's not as though sched_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: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/riscv/include/asm/timex.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
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Patch

diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index 507cae273bc6..5b802755ca3a 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -7,6 +7,7 @@ 
 #define _ASM_RISCV_TIMEX_H
 
 #include <asm/csr.h>
+#include <linux/sched/clock.h>
 
 typedef unsigned long cycles_t;
 
@@ -41,7 +42,7 @@  static inline u32 get_cycles_hi(void)
 static inline unsigned long random_get_entropy(void)
 {
 	if (unlikely(clint_time_val == NULL))
-		return 0;
+		return sched_clock();
 	return get_cycles();
 }
 #define random_get_entropy()	random_get_entropy()