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[v2,04/11] riscv: use ktime_read_raw_clock() for random_get_entropy() instead of zero

Message ID 20220410214951.55294-5-Jason@zx2c4.com
State New
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: 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 | 2 +-
 1 file changed, 1 insertion(+), 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..b320afede88a 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -41,7 +41,7 @@  static inline u32 get_cycles_hi(void)
 static inline unsigned long random_get_entropy(void)
 {
 	if (unlikely(clint_time_val == NULL))
-		return 0;
+		return ktime_read_raw_clock();
 	return get_cycles();
 }
 #define random_get_entropy()	random_get_entropy()