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[v2,07/11] nios2: use ktime_read_raw_clock() for random_get_entropy() instead of zero

Message ID 20220410214951.55294-8-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: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/nios2/include/asm/timex.h | 2 ++
 1 file changed, 2 insertions(+)
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Patch

diff --git a/arch/nios2/include/asm/timex.h b/arch/nios2/include/asm/timex.h
index a769f871b28d..3c74d3e337a0 100644
--- a/arch/nios2/include/asm/timex.h
+++ b/arch/nios2/include/asm/timex.h
@@ -9,4 +9,6 @@  typedef unsigned long cycles_t;
 
 extern cycles_t get_cycles(void);
 
+#define random_get_entropy() ((unsigned long)(get_cycles() ?: ktime_read_raw_clock()))
+
 #endif