From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED9F3C433DB for ; Mon, 4 Jan 2021 19:10:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B8FBC20770 for ; Mon, 4 Jan 2021 19:10:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727086AbhADTKc (ORCPT ); Mon, 4 Jan 2021 14:10:32 -0500 Received: from mail.kernel.org ([198.145.29.99]:53616 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725921AbhADTKb (ORCPT ); Mon, 4 Jan 2021 14:10:31 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 88E8322209 for ; Mon, 4 Jan 2021 19:09:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1609787390; bh=OHuh148jOKPEulSlvw5IYKH1oxCndInHtShLYWJLaXc=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=uBntkJ8VSOzVblaDCOCxpyLcLBpMy1znfEjla5VZyepGC8Mobs6dQ/ohxikYgQdIM WMzWaZxeO4K2aVY8PKf4M682i7cyvkyRkGvBXqa6BLFDZzOSWMmaFpeaks0m8f29bV cR8ZscW8LazyASkWSg1ciMnpb7EL864v1IS0UhJj39+RRhjOdmqNfhvzv6LbEIQmvt DKwNWKWOk0reIqBQWlkF2OdjyUeuPMQzgtHU9/GOEdKzYjmBiBfBIXaiVnBBbiqNan zsF8gDSfuzEjq9SK7nO6pihMQqFQ1m5paZjPmXNX2kW9z7jSjkvjzzGdFEJzQiVzYs DKEEhNZTjWaHQ== Received: by mail-ot1-f45.google.com with SMTP id 11so26998351oty.9 for ; Mon, 04 Jan 2021 11:09:50 -0800 (PST) X-Gm-Message-State: AOAM5318ONM2sU4QQBsNjAJa3S6Zs8hZxRGqc0G5ZwQZQmiL+NpN3LdD SBzSTb7x2Sp26z+9giPcFM2jXbfvPg/rhsWK2P0= X-Google-Smtp-Source: ABdhPJzaDkVryYR0uNwcPevg08CQZGTU7QnlT9iSLuII6HtQIaTcaOCsKeGiskNNcNz4DTYYy2/X4tvBOMf6/vmPYwo= X-Received: by 2002:a05:6830:10d2:: with SMTP id z18mr53281770oto.90.1609787389842; Mon, 04 Jan 2021 11:09:49 -0800 (PST) MIME-Version: 1.0 References: <20201105152944.16953-1-ardb@kernel.org> In-Reply-To: From: Ard Biesheuvel Date: Mon, 4 Jan 2021 20:09:39 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] random: avoid arch_get_random_seed_long() when collecting IRQ randomness To: "Theodore Y. Ts'o" , Eric Biggers Cc: Linux Kernel Mailing List , Linux ARM , Marc Zyngier , Mark Rutland , Mark Brown , Andre Przywara Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 17 Nov 2020 at 14:33, Ard Biesheuvel wrote: > > On Wed, 11 Nov 2020 at 09:19, Ard Biesheuvel wrote: > > > > (+ Eric) > > > > On Thu, 5 Nov 2020 at 16:29, Ard Biesheuvel wrote: > > > > > > When reseeding the CRNG periodically, arch_get_random_seed_long() is > > > called to obtain entropy from an architecture specific source if one > > > is implemented. In most cases, these are special instructions, but in > > > some cases, such as on ARM, we may want to back this using firmware > > > calls, which are considerably more expensive. > > > > > > Another call to arch_get_random_seed_long() exists in the CRNG driver, > > > in add_interrupt_randomness(), which collects entropy by capturing > > > inter-interrupt timing and relying on interrupt jitter to provide > > > random bits. This is done by keeping a per-CPU state, and mixing in > > > the IRQ number, the cycle counter and the return address every time an > > > interrupt is taken, and mixing this per-CPU state into the entropy pool > > > every 64 invocations, or at least once per second. The entropy that is > > > gathered this way is credited as 1 bit of entropy. Every time this > > > happens, arch_get_random_seed_long() is invoked, and the result is > > > mixed in as well, and also credited with 1 bit of entropy. > > > > > > This means that arch_get_random_seed_long() is called at least once > > > per second on every CPU, which seems excessive, and doesn't really > > > scale, especially in a virtualization scenario where CPUs may be > > > oversubscribed: in cases where arch_get_random_seed_long() is backed > > > by an instruction that actually goes back to a shared hardware entropy > > > source (such as RNDRRS on ARM), we will end up hitting it hundreds of > > > times per second. > > > > > > So let's drop the call to arch_get_random_seed_long() from > > > add_interrupt_randomness(), and instead, rely on crng_reseed() to call > > > the arch hook to get random seed material from the platform. > > > > > > Signed-off-by: Ard Biesheuvel > > > --- > > > drivers/char/random.c | 15 +-------------- > > > 1 file changed, 1 insertion(+), 14 deletions(-) > > > > > > diff --git a/drivers/char/random.c b/drivers/char/random.c > > > index 2a41b21623ae..a9c393c1466d 100644 > > > --- a/drivers/char/random.c > > > +++ b/drivers/char/random.c > > > @@ -1261,8 +1261,6 @@ void add_interrupt_randomness(int irq, int irq_flags) > > > cycles_t cycles = random_get_entropy(); > > > __u32 c_high, j_high; > > > __u64 ip; > > > - unsigned long seed; > > > - int credit = 0; > > > > > > if (cycles == 0) > > > cycles = get_reg(fast_pool, regs); > > > @@ -1298,23 +1296,12 @@ void add_interrupt_randomness(int irq, int irq_flags) > > > > > > fast_pool->last = now; > > > __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool)); > > > - > > > - /* > > > - * If we have architectural seed generator, produce a seed and > > > - * add it to the pool. For the sake of paranoia don't let the > > > - * architectural seed generator dominate the input from the > > > - * interrupt noise. > > > - */ > > > - if (arch_get_random_seed_long(&seed)) { > > > - __mix_pool_bytes(r, &seed, sizeof(seed)); > > > - credit = 1; > > > - } > > > spin_unlock(&r->lock); > > > > > > fast_pool->count = 0; > > > > > > /* award one bit for the contents of the fast pool */ > > > - credit_entropy_bits(r, credit + 1); > > > + credit_entropy_bits(r, 1); > > > } > > > EXPORT_SYMBOL_GPL(add_interrupt_randomness); > > > > > > -- > > > 2.17.1 > > > > > Ping? Ping? From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A443C433DB for ; Mon, 4 Jan 2021 19:11:26 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C82C520754 for ; Mon, 4 Jan 2021 19:11:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C82C520754 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:To:Subject:Message-ID:Date:From:In-Reply-To: References:MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ONnZTyioUku4WGTzJv5jj7YXqOd1q5vwJK3krrgDOWI=; b=WRJ1LRlkAVQOlmeHlTt5YnbaP /OOWFwDZcO3yrZZ2EPRJDzgatjh0CQdGTpvVh1jK7O+3aJlFX96O2SRBR//+kcMIzRbmSLdAfG3wF OpEdnJ7Nr8HePPUpFZ2u9aEartLXyn15CwoKRS4OoD8goMkOpyvWvUG7WMFmg/yzwcg4yKrYILnLe ZxyddiUvAeqjW9w2QAhIA2xAdMFhnMdpBQT0n5gFCt15eZ2CIyyKbMJGHHJDJNi4+HLHwTkFzCd/V 92iaBn1djH60Qlxs9XKrnEgsznk0Gm4fihKtYh0hZ2J4iIhw3nZynLnEWNS6tVlH5LliPD1Vw3GQ8 6cbEvNlcg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kwVEn-0007E1-Na; Mon, 04 Jan 2021 19:09:53 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kwVEl-0007Df-Mo for linux-arm-kernel@lists.infradead.org; Mon, 04 Jan 2021 19:09:52 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8394021D93 for ; Mon, 4 Jan 2021 19:09:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1609787390; bh=OHuh148jOKPEulSlvw5IYKH1oxCndInHtShLYWJLaXc=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=uBntkJ8VSOzVblaDCOCxpyLcLBpMy1znfEjla5VZyepGC8Mobs6dQ/ohxikYgQdIM WMzWaZxeO4K2aVY8PKf4M682i7cyvkyRkGvBXqa6BLFDZzOSWMmaFpeaks0m8f29bV cR8ZscW8LazyASkWSg1ciMnpb7EL864v1IS0UhJj39+RRhjOdmqNfhvzv6LbEIQmvt DKwNWKWOk0reIqBQWlkF2OdjyUeuPMQzgtHU9/GOEdKzYjmBiBfBIXaiVnBBbiqNan zsF8gDSfuzEjq9SK7nO6pihMQqFQ1m5paZjPmXNX2kW9z7jSjkvjzzGdFEJzQiVzYs DKEEhNZTjWaHQ== Received: by mail-ot1-f43.google.com with SMTP id d20so27072739otl.3 for ; Mon, 04 Jan 2021 11:09:50 -0800 (PST) X-Gm-Message-State: AOAM531CaPnrtFVmLAdlONTHsuRl2o4v2Xtd3K4ePrwgA3ojSGQCT45D RiwQZV0jG0smW+4fSUsL26LqcE5z4HMVUJYwo7Q= X-Google-Smtp-Source: ABdhPJzaDkVryYR0uNwcPevg08CQZGTU7QnlT9iSLuII6HtQIaTcaOCsKeGiskNNcNz4DTYYy2/X4tvBOMf6/vmPYwo= X-Received: by 2002:a05:6830:10d2:: with SMTP id z18mr53281770oto.90.1609787389842; Mon, 04 Jan 2021 11:09:49 -0800 (PST) MIME-Version: 1.0 References: <20201105152944.16953-1-ardb@kernel.org> In-Reply-To: From: Ard Biesheuvel Date: Mon, 4 Jan 2021 20:09:39 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] random: avoid arch_get_random_seed_long() when collecting IRQ randomness To: "Theodore Y. Ts'o" , Eric Biggers X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210104_140951_878661_F5845D20 X-CRM114-Status: GOOD ( 35.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Marc Zyngier , Linux Kernel Mailing List , Mark Brown , Andre Przywara , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 17 Nov 2020 at 14:33, Ard Biesheuvel wrote: > > On Wed, 11 Nov 2020 at 09:19, Ard Biesheuvel wrote: > > > > (+ Eric) > > > > On Thu, 5 Nov 2020 at 16:29, Ard Biesheuvel wrote: > > > > > > When reseeding the CRNG periodically, arch_get_random_seed_long() is > > > called to obtain entropy from an architecture specific source if one > > > is implemented. In most cases, these are special instructions, but in > > > some cases, such as on ARM, we may want to back this using firmware > > > calls, which are considerably more expensive. > > > > > > Another call to arch_get_random_seed_long() exists in the CRNG driver, > > > in add_interrupt_randomness(), which collects entropy by capturing > > > inter-interrupt timing and relying on interrupt jitter to provide > > > random bits. This is done by keeping a per-CPU state, and mixing in > > > the IRQ number, the cycle counter and the return address every time an > > > interrupt is taken, and mixing this per-CPU state into the entropy pool > > > every 64 invocations, or at least once per second. The entropy that is > > > gathered this way is credited as 1 bit of entropy. Every time this > > > happens, arch_get_random_seed_long() is invoked, and the result is > > > mixed in as well, and also credited with 1 bit of entropy. > > > > > > This means that arch_get_random_seed_long() is called at least once > > > per second on every CPU, which seems excessive, and doesn't really > > > scale, especially in a virtualization scenario where CPUs may be > > > oversubscribed: in cases where arch_get_random_seed_long() is backed > > > by an instruction that actually goes back to a shared hardware entropy > > > source (such as RNDRRS on ARM), we will end up hitting it hundreds of > > > times per second. > > > > > > So let's drop the call to arch_get_random_seed_long() from > > > add_interrupt_randomness(), and instead, rely on crng_reseed() to call > > > the arch hook to get random seed material from the platform. > > > > > > Signed-off-by: Ard Biesheuvel > > > --- > > > drivers/char/random.c | 15 +-------------- > > > 1 file changed, 1 insertion(+), 14 deletions(-) > > > > > > diff --git a/drivers/char/random.c b/drivers/char/random.c > > > index 2a41b21623ae..a9c393c1466d 100644 > > > --- a/drivers/char/random.c > > > +++ b/drivers/char/random.c > > > @@ -1261,8 +1261,6 @@ void add_interrupt_randomness(int irq, int irq_flags) > > > cycles_t cycles = random_get_entropy(); > > > __u32 c_high, j_high; > > > __u64 ip; > > > - unsigned long seed; > > > - int credit = 0; > > > > > > if (cycles == 0) > > > cycles = get_reg(fast_pool, regs); > > > @@ -1298,23 +1296,12 @@ void add_interrupt_randomness(int irq, int irq_flags) > > > > > > fast_pool->last = now; > > > __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool)); > > > - > > > - /* > > > - * If we have architectural seed generator, produce a seed and > > > - * add it to the pool. For the sake of paranoia don't let the > > > - * architectural seed generator dominate the input from the > > > - * interrupt noise. > > > - */ > > > - if (arch_get_random_seed_long(&seed)) { > > > - __mix_pool_bytes(r, &seed, sizeof(seed)); > > > - credit = 1; > > > - } > > > spin_unlock(&r->lock); > > > > > > fast_pool->count = 0; > > > > > > /* award one bit for the contents of the fast pool */ > > > - credit_entropy_bits(r, credit + 1); > > > + credit_entropy_bits(r, 1); > > > } > > > EXPORT_SYMBOL_GPL(add_interrupt_randomness); > > > > > > -- > > > 2.17.1 > > > > > Ping? Ping? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel