From patchwork Tue Apr 12 17:27:45 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: 12811028 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5A47FC433FE for ; Tue, 12 Apr 2022 17:33:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Vk3aOgKGEID6d79RTRIhgj+lnCie7lrwGFZMkzMwHb4=; b=FYMij4vVtuLT1j akw4dRJoGDsUUS0O1QMM0qsPjU6E0XaGplO+sq1IvEf25a/kjvswerO0MyTP/Brw/Qz/CR1T748wJ ZDFC9cU6dXhyZTcIorJD61Lz7cTOGP9ELm6mbuMmw5YYaMsm/oL1IooI9pnok8mI0FLMFo7SLt7qP 78tSwQy/GjYDzNHPIlCwBhRyhCyA98KHm9bnjiUAjsRuv+Qkh3SIopgs3IObX7GycUGU+6VE7JwCO BZxcI17JuZAA1EgYZS7QqauSHI4KFE5dt4dOsms9GFiIoON5sSgmAicvpN4UMgrapXZ/4oAhNH9MY IjDJ9NNvN3+LO/GqUmCg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1neKOG-00FFiY-MS; Tue, 12 Apr 2022 17:33:20 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1neKKN-00FDg2-M4; Tue, 12 Apr 2022 17:29:22 +0000 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 dfw.source.kernel.org (Postfix) with ESMTPS id 161C4619D7; Tue, 12 Apr 2022 17:29:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F3718C385A1; Tue, 12 Apr 2022 17:29:14 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="XhmLqY0q" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1649784554; 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: in-reply-to:in-reply-to:references:references; bh=rw2km/j4ZuUlnKo2vVYlFVdbO5S6naX3px3dcmvw66g=; b=XhmLqY0qe1pwQJi7+OCT7xDbpPRkfS2VLozQIUzCVzDnx6xqMTN1U51vNgZdshxXndw9xo THtZNbm1HJB3ANhoxI8q3Ckzz4DyI+/TctpbHZRP7Ja6JmgnLAC+P5gjvlm77y2Ovq4t0f soMpVlPIPsMvrH1BhCNp2+NAAVrNAHw= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id f34e683e (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Tue, 12 Apr 2022 17:29:14 +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 v3 01/10] timekeeping: add raw clock fallback for random_get_entropy() Date: Tue, 12 Apr 2022 19:27:45 +0200 Message-Id: <20220412172754.149498-2-Jason@zx2c4.com> In-Reply-To: <20220412172754.149498-1-Jason@zx2c4.com> References: <20220412172754.149498-1-Jason@zx2c4.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220412_102919_890964_792EBE10 X-CRM114-Status: GOOD ( 20.33 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org The addition of random_get_entropy_fallback() provides access to whichever time source has the highest frequency, which is useful for gathering entropy on platforms without available cycle counters. It's not necessarily as good as being able to quickly access a cycle counter that the CPU has, but it's still something, even when it falls back to being jiffies-based. In the event that a given arch does not define get_cycles(), falling back to the get_cycles() default implementation that returns 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: Theodore Ts'o Signed-off-by: Jason A. Donenfeld --- include/linux/timex.h | 8 ++++++++ kernel/time/timekeeping.c | 10 ++++++++++ 2 files changed, 18 insertions(+) diff --git a/include/linux/timex.h b/include/linux/timex.h index 5745c90c8800..fbbe34226044 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -62,6 +62,8 @@ #include #include +extern unsigned long random_get_entropy_fallback(void); + #include #ifndef random_get_entropy @@ -74,8 +76,14 @@ * * By default we use get_cycles() for this purpose, but individual * architectures may override this in their asm/timex.h header file. + * If a given arch does not have get_cycles(), then we fallback to + * using random_get_entropy_fallback(). */ +#ifdef get_cycles #define random_get_entropy() ((unsigned long)get_cycles()) +#else +#define random_get_entropy() random_get_entropy_fallback() +#endif #endif /* diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index dcdcb85121e4..7372d60c7c65 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -17,6 +17,7 @@ #include #include #include +#include #include #include #include @@ -2380,6 +2381,15 @@ static int timekeeping_validate_timex(const struct __kernel_timex *txc) return 0; } +/** + * random_get_entropy_fallback - Returns the raw clock source value, + * used by random.c for platforms with no valid random_get_entropy(). + */ +unsigned long random_get_entropy_fallback(void) +{ + return tk_clock_read(&tk_core.timekeeper.tkr_mono); +} +EXPORT_SYMBOL(random_get_entropy_fallback); /** * do_adjtimex() - Accessor function to NTP __do_adjtimex function