linux-kernel - [PATCH 5.17 081/111] um: use fallback for random_get

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Date:   Fri, 27 May 2022 10:49:53 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 5.17 081/111] um: use fallback for random_get_entropy() instead of zero

From: "Jason A. Donenfeld" <Jason@...c4.com>

commit 9f13fb0cd11ed2327abff69f6501a2c124c88b5a upstream.

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 random_get_entropy_fallback() would be
preferable, because that always needs to return _something_, even
falling back to jiffies eventually. It's not as though
random_get_entropy_fallback() 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.

This is accomplished by just including the asm-generic code like on
other architectures, which means we can get rid of the empty stub
function here.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Richard Weinberger <richard@....at>
Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
Acked-by: Johannes Berg <johannes@...solutions.net>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/um/include/asm/timex.h |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

--- a/arch/um/include/asm/timex.h
+++ b/arch/um/include/asm/timex.h
@@ -2,13 +2,8 @@
 #ifndef __UM_TIMEX_H
 #define __UM_TIMEX_H

-typedef unsigned long cycles_t;
-
-static inline cycles_t get_cycles (void)
-{
-	return 0;
-}
-
 #define CLOCK_TICK_RATE (HZ)

+#include <asm-generic/timex.h>
+
 #endif