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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 60145C433F5 for ; Fri, 25 Feb 2022 11:31:50 +0000 (UTC) Received: from localhost ([::1]:37234 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nNYpB-00065J-9l for qemu-devel@archiver.kernel.org; Fri, 25 Feb 2022 06:31:49 -0500 Received: from eggs.gnu.org ([209.51.188.92]:35266) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nNYjv-0003Nk-NL for qemu-devel@nongnu.org; Fri, 25 Feb 2022 06:26:23 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:40910) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nNYjs-0002Hm-BB for qemu-devel@nongnu.org; Fri, 25 Feb 2022 06:26:22 -0500 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 70168B82F20 for ; Fri, 25 Feb 2022 11:26:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8FED9C340FA for ; Fri, 25 Feb 2022 11:26:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1645788375; bh=wzU3M2wR8N6ReWJ/Q5n9T+IQ6J/c41uNq6io2nvM+hE=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=oXJXqMtMjHQKw8ya3RKVksHPcEVUS9mYthZaQwg4YsV+ZHvA9y+xb6lIq58470mRa pbKfYgAY8dI0bCTjJnzSFQZq6UGCdliRokkwVRh0CgG9uAtP/l0UfMs9PBsy71HfMT d/q+zNzA9kPlO0XrR2xDlQAgpu4ojK/in5mkEndmcaS55zvSXqLF7lZt1F8e9GrI+Y 5tdhG/z3NxB+Dh6zONoL1ZGA6WKb6LCeiKBamkV+dxGOk05rFoXBuGQ/DctOBGuzlg MetCIK4BYAXPnFb6C7WG0Pd5FmRGv7enYoF+6nqdzeeUo5Ok4DuLHteGdNX1J2Q2p6 XmriU0DJCVOuA== Received: by mail-yw1-f172.google.com with SMTP id 00721157ae682-2d07c4a0d06so29535097b3.13 for ; Fri, 25 Feb 2022 03:26:15 -0800 (PST) X-Gm-Message-State: AOAM532XTQqJ/+U+WY9JOplqzShwVB0NMh1/slDuQJRspB+pi4oPYCEG 0OfaxptQ4N68C1VFsERSN6i3bnmQITqcXmSzjoA= X-Google-Smtp-Source: ABdhPJwIQZC9GDI5dYoHZxDvQWsfz96l2SZn3EH3J8+1jUaINvs7quVPjznmaJ/ej9wycL9PBKnx7quCWRYwgWRAJEQ= X-Received: by 2002:a81:7d04:0:b0:2d0:d0e2:126f with SMTP id y4-20020a817d04000000b002d0d0e2126fmr6861642ywc.485.1645788374561; Fri, 25 Feb 2022 03:26:14 -0800 (PST) MIME-Version: 1.0 References: <20220224133906.751587-1-Jason@zx2c4.com> <20220224133906.751587-2-Jason@zx2c4.com> In-Reply-To: <20220224133906.751587-2-Jason@zx2c4.com> From: Ard Biesheuvel Date: Fri, 25 Feb 2022 12:26:03 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 1/2] random: add mechanism for VM forks to reinitialize crng To: "Jason A. Donenfeld" Content-Type: text/plain; charset="UTF-8" Received-SPF: pass client-ip=145.40.68.75; envelope-from=ardb@kernel.org; helo=ams.source.kernel.org X-Spam_score_int: -71 X-Spam_score: -7.2 X-Spam_bar: ------- X-Spam_report: (-7.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-hyperv@vger.kernel.org, kvm@vger.kernel.org, "Michael S. Tsirkin" , raduweis@amazon.com, QEMU Developers , Dominik Brodowski , KY Srinivasan , Wei Liu , Stephen Hemminger , ben@skyportsystems.com, Eric Biggers , Dexuan Cui , Eric Biggers , Laszlo Ersek , Eduardo Habkost , adrian@parity.io, Jann Horn , Haiyang Zhang , Alexander Graf , "Theodore Y. Ts'o" , colmmacc@amazon.com, berrange@redhat.com, Greg Kroah-Hartman , Linux Kernel Mailing List , Linux Crypto Mailing List , Igor Mammedov , dwmw@amazon.co.uk Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 24 Feb 2022 at 14:39, Jason A. Donenfeld wrote: > > When a VM forks, we must immediately mix in additional information to > the stream of random output so that two forks or a rollback don't > produce the same stream of random numbers, which could have catastrophic > cryptographic consequences. This commit adds a simple API, add_vmfork_ > randomness(), for that, by force reseeding the crng. > > This has the added benefit of also draining the entropy pool and setting > its timer back, so that any old entropy that was there prior -- which > could have already been used by a different fork, or generally gone > stale -- does not contribute to the accounting of the next 256 bits. > > Cc: Dominik Brodowski > Cc: Theodore Ts'o > Cc: Jann Horn > Cc: Eric Biggers > Signed-off-by: Jason A. Donenfeld Acked-by: Ard Biesheuvel > --- > drivers/char/random.c | 50 +++++++++++++++++++++++++++++------------- > include/linux/random.h | 1 + > 2 files changed, 36 insertions(+), 15 deletions(-) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 9fb06fc298d3..e8b84791cefe 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -289,14 +289,14 @@ static DEFINE_PER_CPU(struct crng, crngs) = { > }; > > /* Used by crng_reseed() to extract a new seed from the input pool. */ > -static bool drain_entropy(void *buf, size_t nbytes); > +static bool drain_entropy(void *buf, size_t nbytes, bool force); > > /* > * This extracts a new crng key from the input pool, but only if there is a > - * sufficient amount of entropy available, in order to mitigate bruteforcing > - * of newly added bits. > + * sufficient amount of entropy available or force is true, in order to > + * mitigate bruteforcing of newly added bits. > */ > -static void crng_reseed(void) > +static void crng_reseed(bool force) > { > unsigned long flags; > unsigned long next_gen; > @@ -304,7 +304,7 @@ static void crng_reseed(void) > bool finalize_init = false; > > /* Only reseed if we can, to prevent brute forcing a small amount of new bits. */ > - if (!drain_entropy(key, sizeof(key))) > + if (!drain_entropy(key, sizeof(key), force)) > return; > > /* > @@ -406,7 +406,7 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], > * in turn bumps the generation counter that we check below. > */ > if (unlikely(time_after(jiffies, READ_ONCE(base_crng.birth) + CRNG_RESEED_INTERVAL))) > - crng_reseed(); > + crng_reseed(false); > > local_lock_irqsave(&crngs.lock, flags); > crng = raw_cpu_ptr(&crngs); > @@ -771,10 +771,10 @@ EXPORT_SYMBOL(get_random_bytes_arch); > * > * Finally, extract entropy via these two, with the latter one > * setting the entropy count to zero and extracting only if there > - * is POOL_MIN_BITS entropy credited prior: > + * is POOL_MIN_BITS entropy credited prior or force is true: > * > * static void extract_entropy(void *buf, size_t nbytes) > - * static bool drain_entropy(void *buf, size_t nbytes) > + * static bool drain_entropy(void *buf, size_t nbytes, bool force) > * > **********************************************************************/ > > @@ -832,7 +832,7 @@ static void credit_entropy_bits(size_t nbits) > } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); > > if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) > - crng_reseed(); > + crng_reseed(false); > } > > /* > @@ -882,16 +882,16 @@ static void extract_entropy(void *buf, size_t nbytes) > } > > /* > - * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we > - * set the entropy count to zero (but don't actually touch any data). Only then > - * can we extract a new key with extract_entropy(). > + * First we make sure we have POOL_MIN_BITS of entropy in the pool unless force > + * is true, and then we set the entropy count to zero (but don't actually touch > + * any data). Only then can we extract a new key with extract_entropy(). > */ > -static bool drain_entropy(void *buf, size_t nbytes) > +static bool drain_entropy(void *buf, size_t nbytes, bool force) > { > unsigned int entropy_count; > do { > entropy_count = READ_ONCE(input_pool.entropy_count); > - if (entropy_count < POOL_MIN_BITS) > + if (!force && entropy_count < POOL_MIN_BITS) > return false; > } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); > extract_entropy(buf, nbytes); > @@ -915,6 +915,7 @@ static bool drain_entropy(void *buf, size_t nbytes) > * void add_hwgenerator_randomness(const void *buffer, size_t count, > * size_t entropy); > * void add_bootloader_randomness(const void *buf, size_t size); > + * void add_vmfork_randomness(const void *unique_vm_id, size_t size); > * void add_interrupt_randomness(int irq); > * > * add_device_randomness() adds data to the input pool that > @@ -946,6 +947,10 @@ static bool drain_entropy(void *buf, size_t nbytes) > * add_device_randomness(), depending on whether or not the configuration > * option CONFIG_RANDOM_TRUST_BOOTLOADER is set. > * > + * add_vmfork_randomness() adds a unique (but not necessarily secret) ID > + * representing the current instance of a VM to the pool, without crediting, > + * and then force-reseeds the crng so that it takes effect immediately. > + * > * add_interrupt_randomness() uses the interrupt timing as random > * inputs to the entropy pool. Using the cycle counters and the irq source > * as inputs, it feeds the input pool roughly once a second or after 64 > @@ -1175,6 +1180,21 @@ void add_bootloader_randomness(const void *buf, size_t size) > } > EXPORT_SYMBOL_GPL(add_bootloader_randomness); > > +/* > + * Handle a new unique VM ID, which is unique, not secret, so we > + * don't credit it, but we do immediately force a reseed after so > + * that it's used by the crng posthaste. > + */ > +void add_vmfork_randomness(const void *unique_vm_id, size_t size) > +{ > + add_device_randomness(unique_vm_id, size); > + if (crng_ready()) { > + crng_reseed(true); > + pr_notice("crng reseeded due to virtual machine fork\n"); > + } > +} > +EXPORT_SYMBOL_GPL(add_vmfork_randomness); > + > struct fast_pool { > union { > u32 pool32[4]; > @@ -1564,7 +1584,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) > return -EPERM; > if (crng_init < 2) > return -ENODATA; > - crng_reseed(); > + crng_reseed(false); > return 0; > default: > return -EINVAL; > diff --git a/include/linux/random.h b/include/linux/random.h > index 6148b8d1ccf3..51b8ed797732 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -34,6 +34,7 @@ extern void add_input_randomness(unsigned int type, unsigned int code, > extern void add_interrupt_randomness(int irq) __latent_entropy; > extern void add_hwgenerator_randomness(const void *buffer, size_t count, > size_t entropy); > +extern void add_vmfork_randomness(const void *unique_vm_id, size_t size); > > extern void get_random_bytes(void *buf, size_t nbytes); > extern int wait_for_random_bytes(void); > -- > 2.35.1 >