From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <3dee9e8f-45c5-49a0-a19e-d67917fd6bb3@kernel.org> Date: Mon, 2 May 2022 16:01:05 -0500 MIME-Version: 1.0 Subject: Re: [PATCH v5 06/11] nios2: use fallback for random_get_entropy() instead of zero Content-Language: en-US References: <20220419111650.1582274-1-Jason@zx2c4.com> <20220419111650.1582274-7-Jason@zx2c4.com> From: Dinh Nguyen In-Reply-To: <20220419111650.1582274-7-Jason@zx2c4.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit To: "Jason A. Donenfeld" , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, tglx@linutronix.de, arnd@arndb.de Cc: Theodore Ts'o , Dominik Brodowski , Russell King , Catalin Marinas , Will Deacon , Geert Uytterhoeven , Thomas Bogendoerfer , Paul Walmsley , Palmer Dabbelt , Albert Ou , "David S . Miller" , Richard Weinberger , Anton Ivanov , Johannes Berg , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Chris Zankel , Max Filippov , Stephen Boyd , 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 List-ID: On 4/19/22 06:16, Jason A. Donenfeld wrote: > 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 > Cc: Arnd Bergmann > Cc: Dinh Nguyen > Signed-off-by: Jason A. Donenfeld > --- > arch/nios2/include/asm/timex.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/nios2/include/asm/timex.h b/arch/nios2/include/asm/timex.h > index a769f871b28d..d9a3f426cdda 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()) ?: random_get_entropy_fallback()) > + > #endif Acked-by: Dinh Nguyen