linux-kernel - [PATCH v6 11/17] openrisc: use fallback for random_get

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Message-Id: <20220423212623.1957011-12-Jason@zx2c4.com>
Date:   Sat, 23 Apr 2022 23:26:17 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        tglx@...utronix.de, arnd@...db.de
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>
Subject: [PATCH v6 11/17] openrisc: use fallback for random_get_entropy() instead of zero

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.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Jonas Bonn <jonas@...thpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
Cc: Stafford Horne <shorne@...il.com>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 arch/openrisc/include/asm/timex.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/openrisc/include/asm/timex.h b/arch/openrisc/include/asm/timex.h
index d52b4e536e3f..115e89b336cd 100644
--- a/arch/openrisc/include/asm/timex.h
+++ b/arch/openrisc/include/asm/timex.h
@@ -23,6 +23,9 @@ static inline cycles_t get_cycles(void)
 {
 	return mfspr(SPR_TTCR);
 }
+#define get_cycles get_cycles
+
+#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback())
 
 /* This isn't really used any more */
 #define CLOCK_TICK_RATE 1000
-- 
2.35.1