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[RFC,v1,04/10] mips: use sched_clock() for random_get_entropy() instead of zero

Message ID 20220408182145.142506-5-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: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/mips/include/asm/timex.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
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Patch

diff --git a/arch/mips/include/asm/timex.h b/arch/mips/include/asm/timex.h
index b05bb70a2e46..1de8ded08bb7 100644
--- a/arch/mips/include/asm/timex.h
+++ b/arch/mips/include/asm/timex.h
@@ -12,6 +12,7 @@ 
 #ifdef __KERNEL__
 
 #include <linux/compiler.h>
+#include <linux/sched/clock.h>
 
 #include <asm/cpu.h>
 #include <asm/cpu-features.h>
@@ -94,7 +95,7 @@  static inline unsigned long random_get_entropy(void)
 	else if (likely(imp != PRID_IMP_R6000 && imp != PRID_IMP_R6000A))
 		return read_c0_random();
 	else
-		return 0;	/* no usable register */
+		return sched_clock();	/* no usable register */
 }
 #define random_get_entropy random_get_entropy