From patchwork Wed Feb 23 22:04:55 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: 12757535 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 72F83C4332F for ; Wed, 23 Feb 2022 22:05:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243226AbiBWWFz (ORCPT ); Wed, 23 Feb 2022 17:05:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42088 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243209AbiBWWFy (ORCPT ); Wed, 23 Feb 2022 17:05:54 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DFA274DF62; Wed, 23 Feb 2022 14:05:21 -0800 (PST) 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 D9C246190C; Wed, 23 Feb 2022 22:05:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06768C340E7; Wed, 23 Feb 2022 22:05:17 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="awY7NnOu" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1645653917; 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=P4ovfwdUD1X2Y5KbzB3Em8ah+UEym9W3EkRSqF247no=; b=awY7NnOuzpNXi126ohYHv/dK0AEGJosLdDAfK5B8W8GsL75iQnM7JBOPyYyRcN/ZCqs0r8 sik75qGnqWecorYLRCnHp4iKtGBl/YRO+ppF0bsEyRMs+4+vJumbmwx8oxKpIeo29D5p41 doFEFyydCqOGCkSSdVQwi3A6pgpsGsw= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 5794f5a0 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Wed, 23 Feb 2022 22:05:17 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-hyperv@vger.kernel.org, kvm@vger.kernel.org, linux-crypto@vger.kernel.org, qemu-devel@nongnu.org, linux-kernel@vger.kernel.org Cc: "Jason A. Donenfeld" , adrian@parity.io, dwmw@amazon.co.uk, graf@amazon.com, colmmacc@amazon.com, raduweis@amazon.com, imammedo@redhat.com, ehabkost@redhat.com, ben@skyportsystems.com, mst@redhat.com, kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, linux@dominikbrodowski.net, ardb@kernel.org, jannh@google.com, gregkh@linuxfoundation.org, tytso@mit.edu Subject: [PATCH v2 1/2] random: add mechanism for VM forks to reinitialize crng Date: Wed, 23 Feb 2022 23:04:55 +0100 Message-Id: <20220223220456.666193-2-Jason@zx2c4.com> In-Reply-To: <20220223220456.666193-1-Jason@zx2c4.com> References: <20220223220456.666193-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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. Cc: Dominik Brodowski Cc: Theodore Ts'o Cc: Jann Horn Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 53 ++++++++++++++++++++++++++++++++++++++++++ include/linux/random.h | 1 + 2 files changed, 54 insertions(+) diff --git a/drivers/char/random.c b/drivers/char/random.c index 536237a0f073..95584f6646f9 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -508,6 +508,40 @@ static size_t crng_pre_init_inject(const void *input, size_t len, return len; } +/* + * This mixes unique_vm_id directly into the base_crng key as soon as + * possible, similarly to crng_pre_init_inject(), even if the crng is + * already running, in order to immediately branch streams from prior + * VM instances. + */ +static void crng_vmfork_inject(const void *unique_vm_id, size_t len) +{ + unsigned long flags, next_gen; + struct blake2s_state hash; + + spin_lock_irqsave(&base_crng.lock, flags); + + /* + * Update the generation, while locked, as early as possible + * This will mean unlocked reads of the generation will + * cause a reseeding of per-cpu crngs, and those will spin + * on the base_crng lock waiting for the rest of this function + * to complete, which achieves the goal of blocking the + * production of new output until this is done. + */ + next_gen = base_crng.generation + 1; + if (next_gen == ULONG_MAX) + ++next_gen; + WRITE_ONCE(base_crng.generation, next_gen); + + blake2s_init(&hash, sizeof(base_crng.key)); + blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); + blake2s_update(&hash, unique_vm_id, len); + blake2s_final(&hash, base_crng.key); + + spin_unlock_irqrestore(&base_crng.lock, flags); +} + static void _get_random_bytes(void *buf, size_t nbytes) { u32 chacha_state[CHACHA_STATE_WORDS]; @@ -935,6 +969,7 @@ 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 @@ -966,6 +1001,11 @@ 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 neccessarily secret) ID + * representing the current instance of a VM to the pool, without crediting, + * and then immediately mixes that ID into the current base_crng key, so + * that it takes effect prior to a reseeding. + * * 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 @@ -1195,6 +1235,19 @@ 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 mix it into the entropy pool and + * inject it into the crng. + */ +void add_vmfork_randomness(const void *unique_vm_id, size_t size) +{ + add_device_randomness(unique_vm_id, size); + if (crng_ready()) + crng_vmfork_inject(unique_vm_id, size); +} +EXPORT_SYMBOL_GPL(add_vmfork_randomness); + struct fast_pool { union { u32 pool32[4]; 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);