From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
tglx@linutronix.de, arnd@arndb.de
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
Theodore Ts'o <tytso@mit.edu>,
Dominik Brodowski <linux@dominikbrodowski.net>,
Russell King <linux@armlinux.org.uk>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
"David S . Miller" <davem@davemloft.net>,
Richard Weinberger <richard@nod.at>,
Anton Ivanov <anton.ivanov@cambridgegreys.com>,
Johannes Berg <johannes@sipsolutions.net>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Chris Zankel <chris@zankel.net>,
Max Filippov <jcmvbkbc@gmail.com>,
John Stultz <john.stultz@linaro.org>,
Stephen Boyd <sboyd@kernel.org>,
Dinh Nguyen <dinguyen@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
linux-riscv@lists.infradead.org, sparclinux@vger.kernel.org,
linux-um@lists.infradead.org, x86@kernel.org,
linux-xtensa@linux-xtensa.org
Subject: [PATCH v2 06/11] arm: use ktime_read_raw_clock() for random_get_entropy() instead of zero
Date: Sun, 10 Apr 2022 23:49:46 +0200 [thread overview]
Message-ID: <20220410214951.55294-7-Jason@zx2c4.com> (raw)
In-Reply-To: <20220410214951.55294-1-Jason@zx2c4.com>
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: Russell King <linux@armlinux.org.uk>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
arch/arm/include/asm/timex.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h
index 7c3b3671d6c2..d0b32ce87254 100644
--- a/arch/arm/include/asm/timex.h
+++ b/arch/arm/include/asm/timex.h
@@ -11,5 +11,6 @@
typedef unsigned long cycles_t;
#define get_cycles() ({ cycles_t c; read_current_timer(&c) ? 0 : c; })
+#define random_get_entropy() ((unsigned long)(get_cycles() ?: ktime_read_raw_clock()))
#endif
--
2.35.1
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next prev parent reply other threads:[~2022-04-10 21:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-10 21:49 [PATCH v2 00/11] archs/random: fallback to using ktime_read_raw_clock() if no cycle counter Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 01/11] timekeeping: add accessor for raw clock Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 02/11] timekeeping: use ktime_read_raw_clock() for random_get_entropy() if no get_cycles() Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 03/11] m68k: use ktime_read_raw_clock() for random_get_entropy() instead of zero Jason A. Donenfeld
2022-04-11 8:18 ` Thomas Gleixner
2022-04-11 22:07 ` Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 04/11] riscv: " Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 05/11] mips: " Jason A. Donenfeld
2022-04-10 21:49 ` Jason A. Donenfeld [this message]
2022-04-10 21:49 ` [PATCH v2 07/11] nios2: " Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 08/11] x86: " Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 09/11] um: " Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 10/11] sparc: " Jason A. Donenfeld
2022-04-10 21:49 ` [PATCH v2 11/11] xtensa: " Jason A. Donenfeld
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