From patchwork Sun Apr 10 21:49:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 12808289 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE070C433FE for ; Sun, 10 Apr 2022 21:50:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242694AbiDJVwb (ORCPT ); Sun, 10 Apr 2022 17:52:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40720 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242749AbiDJVw3 (ORCPT ); Sun, 10 Apr 2022 17:52:29 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B93A0F73; Sun, 10 Apr 2022 14:50:17 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 333E7B80D9C; Sun, 10 Apr 2022 21:50:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A83A6C385A1; Sun, 10 Apr 2022 21:50:11 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="pYNzQz9R" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1649627409; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=LJrd+NtDQlznIg8cc0nDb/z2OXp2bjAbSihY/d2tY4E=; b=pYNzQz9RQ5eqsRIdR/NtgerIdGDbtTt3I6e+oJvxWz0XaIbHPRgsz8BXjLJiHUOgL8XO/t LhjsNhsKY4qnkJTuwjXjSD8V1g6T66d0ibvN+V52GUS4nxDOfOUG78O4E3K8pL5Fsp7y74 GcylDa/hG/lBRoQWJyv4JOWd/Cldcz8= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 19f87fe0 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Sun, 10 Apr 2022 21:50:09 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, tglx@linutronix.de, arnd@arndb.de Cc: "Jason A. Donenfeld" , 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 , John Stultz , Stephen Boyd , Dinh Nguyen , 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 00/11] archs/random: fallback to using ktime_read_raw_clock() if no cycle counter Date: Sun, 10 Apr 2022 23:49:40 +0200 Message-Id: <20220410214951.55294-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Hi folks, The RNG uses a function called random_get_entropy() basically anytime that it needs to timestamp an event. For example, an interrupt comes in, and we mix a random_get_entropy() into the entropy pool somehow. Somebody mashes their keyboard or moves their mouse around? We mix a random_get_entropy() into the entropy pool. It's one of the main varieties of input. Unfortunately, it's always 0 on a few platforms. The RNG has accumulated various hacks to deal with this, but in general it's not great. Surely we can do better than 0. In fact, *anything* that's not the same exact value all the time would be better than 0. Even a counter that increments once per hour would be better than 0! I think you get the idea. On most platforms, random_get_entropy() is aliased to get_cycles(), which makes sense for platforms where get_cycles() is defined. RDTSC, for example, has all the characteristics we care about for this function: it's fast to acquire (i.e. acceptable in an irq handler), pretty high precision, available, forms a 2-monotone distribution, etc. But for platforms without that, what is the next best thing? Sometimes the next best thing is architecture-defined. For example, really old MIPS has the CP0 random register, which isn't a cycle counter, but is at least something. However, some platforms don't even have an architecture-defined fallback. Fortunately, the timekeeping subsystem has already solved this problem of trying to determine what the least bad clock is on constrained systems, falling back to jiffies in the worst case. By exporting the raw clock, we can get a decent fallback function for when there's no cycle counter or architecture-specific function. This series makes the RNG more useful on: m68k, RISC-V, MIPS, ARM32, NIOS II, SPARC32, Xtensa, and Usermode Linux. Previously these platforms would, in certain circumstances, but out of luck with regards to having any type of event timestamping source in the RNG. Finally, note that this series isn't about "jitter entropy" or other ways of initializing the RNG. That's a different topic for a different thread. Please don't let this discussion veer off into that. Here, I'm just trying to find a good fallback counter/timer for platforms without get_cycles(), a question with limited scope. If this (or a future revision) looks good to you all and receives the requisite acks, my plan was to take these through the random.git tree for 5.19, so that I can then build on top of it. Thanks, Jason Changes v1->v2: - Use ktime_read_raw_clock() instead of sched_clock(), per Thomas' suggestion. - Drop arm64 change. - Cleanup header inclusion ordering problem. Cc: Thomas Gleixner Cc: Arnd Bergmann Cc: Theodore Ts'o Cc: Dominik Brodowski Cc: Russell King Cc: Catalin Marinas Cc: Will Deacon Cc: Geert Uytterhoeven Cc: Thomas Bogendoerfer Cc: Paul Walmsley Cc: Palmer Dabbelt Cc: Albert Ou Cc: David S. Miller Cc: Richard Weinberger Cc: Anton Ivanov Cc: Johannes Berg Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: H. Peter Anvin Cc: Chris Zankel Cc: Max Filippov Cc: John Stultz Cc: Stephen Boyd Cc: Dinh Nguyen Cc: linux-arm-kernel@lists.infradead.org Cc: linux-m68k@lists.linux-m68k.org Cc: linux-mips@vger.kernel.org Cc: linux-riscv@lists.infradead.org Cc: sparclinux@vger.kernel.org Cc: linux-um@lists.infradead.org Cc: x86@kernel.org Cc: linux-xtensa@linux-xtensa.org Jason A. Donenfeld (11): timekeeping: add accessor for raw clock timekeeping: use ktime_read_raw_clock() for random_get_entropy() if no get_cycles() m68k: use ktime_read_raw_clock() for random_get_entropy() instead of zero riscv: use ktime_read_raw_clock() for random_get_entropy() instead of zero mips: use ktime_read_raw_clock() for random_get_entropy() instead of zero arm: use ktime_read_raw_clock() for random_get_entropy() instead of zero nios2: use ktime_read_raw_clock() for random_get_entropy() instead of zero x86: use ktime_read_raw_clock() for random_get_entropy() instead of zero um: use ktime_read_raw_clock() for random_get_entropy() instead of zero sparc: use ktime_read_raw_clock() for random_get_entropy() instead of zero xtensa: use ktime_read_raw_clock() for random_get_entropy() instead of zero arch/arm/include/asm/timex.h | 1 + arch/m68k/include/asm/timex.h | 2 +- arch/mips/include/asm/timex.h | 2 +- arch/nios2/include/asm/timex.h | 2 ++ arch/riscv/include/asm/timex.h | 2 +- arch/sparc/include/asm/timex_32.h | 4 +--- arch/um/include/asm/timex.h | 9 ++------- arch/x86/include/asm/tsc.h | 10 ++++++++++ arch/xtensa/include/asm/timex.h | 6 ++---- include/linux/timex.h | 8 ++++++++ kernel/time/timekeeping.c | 8 ++++++++ 11 files changed, 37 insertions(+), 17 deletions(-)