From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753534Ab3IWKio (ORCPT ); Mon, 23 Sep 2013 06:38:44 -0400 Received: from mail.eperm.de ([89.247.134.16]:34856 "EHLO mail.eperm.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753355Ab3IWKin (ORCPT ); Mon, 23 Sep 2013 06:38:43 -0400 From: Stephan Mueller To: "Theodore Ts'o" Cc: Linux Kernel Developers List , hpa@zytor.com, joern@logfs.org, macro@linux-mips.org, ralf@linux-mips.org, dave.taht@gmail.com, blogic@openwrt.org, andrewmcgr@gmail.com, geert@linux-m68k.org, tg@mirbsd.de Subject: Re: [PATCH, RFC 07/12] random: allow architectures to optionally define random_get_entropy() Date: Mon, 23 Sep 2013 12:38:26 +0200 Message-ID: <1436634.TJZIP2QOy7@tauon> User-Agent: KMail/4.11.1 (Linux/3.11.1-200.fc19.x86_64; KDE/4.11.1; x86_64; ; ) In-Reply-To: <1379882338-7209-8-git-send-email-tytso@mit.edu> References: <1379882338-7209-1-git-send-email-tytso@mit.edu> <1379882338-7209-8-git-send-email-tytso@mit.edu> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am Sonntag, 22. September 2013, 16:38:53 schrieb Theodore Ts'o: Hi Theodore, >Allow architectures which have a disabled get_cycles() function to >provide a random_get_entropy() function which provides a fine-grained, >rapidly changing counter that can be used by the /dev/random driver. Are there any plans to get such function implemented on large list of architectures without a get_cycles function? Thanks > >For example, an architecture might have a rapidly changing register >used to control random TLB cache eviction, or DRAM refresh that >doesn't meet the requirements of get_cycles(), but which is good >enough for the needs of the random driver. > >Signed-off-by: "Theodore Ts'o" >--- > drivers/char/random.c | 8 ++++---- > include/linux/timex.h | 17 +++++++++++++++++ > 2 files changed, 21 insertions(+), 4 deletions(-) > >diff --git a/drivers/char/random.c b/drivers/char/random.c >index 9564144..ba23d5c 100644 >--- a/drivers/char/random.c >+++ b/drivers/char/random.c >@@ -707,7 +707,7 @@ struct timer_rand_state { > */ > void add_device_randomness(const void *buf, unsigned int size) > { >- unsigned long time = get_cycles() ^ jiffies; >+ unsigned long time = random_get_entropy() ^ jiffies; > unsigned long flags; > > trace_add_device_randomness(size, _RET_IP_); >@@ -751,7 +751,7 @@ static void add_timer_randomness(struct >timer_rand_state *state, unsigned num) goto out; > > sample.jiffies = jiffies; >- sample.cycles = get_cycles(); >+ sample.cycles = random_get_entropy(); > sample.num = num; > mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL); > >@@ -818,7 +818,7 @@ void add_interrupt_randomness(int irq, int >irq_flags) struct fast_pool *fast_pool = >&__get_cpu_var(irq_randomness); struct pt_regs *regs = >get_irq_regs(); > unsigned long now = jiffies; >- __u32 input[4], cycles = get_cycles(); >+ __u32 input[4], cycles = random_get_entropy(); > > input[0] = cycles ^ jiffies; > input[1] = irq; >@@ -1580,7 +1580,7 @@ unsigned int get_random_int(void) > > hash = get_cpu_var(get_random_int_hash); > >- hash[0] += current->pid + jiffies + get_cycles(); >+ hash[0] += current->pid + jiffies + random_get_entropy(); > md5_transform(hash, random_int_secret); > ret = hash[0]; > put_cpu_var(get_random_int_hash); >diff --git a/include/linux/timex.h b/include/linux/timex.h >index b3726e6..f9780cc 100644 >--- a/include/linux/timex.h >+++ b/include/linux/timex.h >@@ -64,6 +64,23 @@ > > #include > >+#ifndef random_get_entropy >+/* >+ * The random_get_entropy() function is used by the /dev/random driver >+ * in order to extract entropy via the relative unpredictability of + >* when an interrupt takes places versus a high speed, fine-grained + * >timing source or cycle counter. Since it will be occurred on every + >* single interrupt, it must have a very low cost/overhead. >+ * >+ * By default we use get_cycles() for this purpose, but individual >+ * architectures may override this in their asm/timex.h header file. >+ */ >+static inline cycles_t random_get_entropy(void) >+{ >+ return get_cycles(); >+} >+#endif >+ > /* > * SHIFT_PLL is used as a dampening factor to define how much we > * adjust the frequency correction for a given offset in PLL mode. Ciao Stephan