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); From patchwork Wed Feb 23 22:04:56 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: 12757536 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 C6214C433F5 for ; Wed, 23 Feb 2022 22:05:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243277AbiBWWGE (ORCPT ); Wed, 23 Feb 2022 17:06:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42232 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243271AbiBWWF5 (ORCPT ); Wed, 23 Feb 2022 17:05:57 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E63684DF62; Wed, 23 Feb 2022 14:05:28 -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 82E5161922; Wed, 23 Feb 2022 22:05:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 869DCC340E7; Wed, 23 Feb 2022 22:05:25 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="bT1dqqnJ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1645653924; 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=a89/Lm75y4Z0GZ9X8KfFu1CUr1fh3dhCCiCALwHdE1I=; b=bT1dqqnJZ0Fe9h5jPfLuxQFCLCzQRHrtr6PotmddfrA9rxzPtLPBsSC06Z9X6w970kXDcj XqDx1UgjwEwt9yJo3LgvBQsD2UdVO62j09jEj20Rq1uMZPfz6A/B6YbLhMBirSL6sOteBx vS7ybKBwp8Ek2YRenF9O8nJfkw4+7uI= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 0f07b509 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Wed, 23 Feb 2022 22:05:23 +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 2/2] virt: vmgenid: introduce driver for reinitializing RNG on VM fork Date: Wed, 23 Feb 2022 23:04:56 +0100 Message-Id: <20220223220456.666193-3-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 VM Generation ID is a feature from Microsoft, described at , and supported by Hyper-V and QEMU. Its usage is described in Microsoft's RNG whitepaper, , as: If the OS is running in a VM, there is a problem that most hypervisors can snapshot the state of the machine and later rewind the VM state to the saved state. This results in the machine running a second time with the exact same RNG state, which leads to serious security problems. To reduce the window of vulnerability, Windows 10 on a Hyper-V VM will detect when the VM state is reset, retrieve a unique (not random) value from the hypervisor, and reseed the root RNG with that unique value. This does not eliminate the vulnerability, but it greatly reduces the time during which the RNG system will produce the same outputs as it did during a previous instantiation of the same VM state. Linux has the same issue, and given that vmgenid is supported already by multiple hypervisors, we can implement more or less the same solution. So this commit wires up the vmgenid ACPI notification to the RNG's newly added add_vmfork_randomness() function. It can be used from qemu via the `-device vmgenid,guid=auto` parameter. After setting that, use `savevm` in the monitor to save the VM state, then quit QEMU, start it again, and use `loadvm`. That will trigger this driver's notify function, which hands the new UUID to the RNG. This driver builds on prior work from Adrian Catangiu at Amazon, and it is my hope that that team can resume maintenance of this driver. Cc: Adrian Catangiu Cc: Dominik Brodowski Cc: Ard Biesheuvel Signed-off-by: Jason A. Donenfeld --- drivers/virt/Kconfig | 9 ++++ drivers/virt/Makefile | 1 + drivers/virt/vmgenid.c | 120 +++++++++++++++++++++++++++++++++++++++++ 3 files changed, 130 insertions(+) create mode 100644 drivers/virt/vmgenid.c diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig index 8061e8ef449f..d3276dc2095c 100644 --- a/drivers/virt/Kconfig +++ b/drivers/virt/Kconfig @@ -13,6 +13,15 @@ menuconfig VIRT_DRIVERS if VIRT_DRIVERS +config VMGENID + tristate "Virtual Machine Generation ID driver" + default y + depends on ACPI + help + Say Y here to use the hypervisor-provided Virtual Machine Generation ID + to reseed the RNG when the VM is cloned. This is highly recommended if + you intend to do any rollback / cloning / snapshotting of VMs. + config FSL_HV_MANAGER tristate "Freescale hypervisor management driver" depends on FSL_SOC diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile index 3e272ea60cd9..108d0ffcc9aa 100644 --- a/drivers/virt/Makefile +++ b/drivers/virt/Makefile @@ -4,6 +4,7 @@ # obj-$(CONFIG_FSL_HV_MANAGER) += fsl_hypervisor.o +obj-$(CONFIG_VMGENID) += vmgenid.o obj-y += vboxguest/ obj-$(CONFIG_NITRO_ENCLAVES) += nitro_enclaves/ diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c new file mode 100644 index 000000000000..c2255ea6be59 --- /dev/null +++ b/drivers/virt/vmgenid.c @@ -0,0 +1,120 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Virtual Machine Generation ID driver + * + * Copyright (C) 2022 Jason A. Donenfeld . All Rights Reserved. + * Copyright (C) 2020 Amazon. All rights reserved. + * Copyright (C) 2018 Red Hat Inc. All rights reserved. + */ + +#include +#include +#include +#include +#include + +ACPI_MODULE_NAME("vmgenid"); + +static struct { + uuid_t this_uuid; + uuid_t *next_uuid; +} state; + +static int vmgenid_acpi_add(struct acpi_device *device) +{ + struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER }; + union acpi_object *pss; + phys_addr_t phys_addr; + acpi_status status; + int ret = 0; + + if (!device) + return -EINVAL; + + status = acpi_evaluate_object(device->handle, "ADDR", NULL, &buffer); + if (ACPI_FAILURE(status)) { + ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR")); + return -ENODEV; + } + pss = buffer.pointer; + if (!pss || pss->type != ACPI_TYPE_PACKAGE || pss->package.count != 2 || + pss->package.elements[0].type != ACPI_TYPE_INTEGER || + pss->package.elements[1].type != ACPI_TYPE_INTEGER) { + ret = -EINVAL; + goto out; + } + + phys_addr = (pss->package.elements[0].integer.value << 0) | + (pss->package.elements[1].integer.value << 32); + state.next_uuid = acpi_os_map_memory(phys_addr, sizeof(*state.next_uuid)); + if (!state.next_uuid) { + ret = -ENOMEM; + goto out; + } + + state.this_uuid = *state.next_uuid; + device->driver_data = &state; + add_device_randomness(&state.this_uuid, sizeof(state.this_uuid)); + +out: + ACPI_FREE(buffer.pointer); + return ret; +} + +static int vmgenid_acpi_remove(struct acpi_device *device) +{ + if (!device || acpi_driver_data(device) != &state) + return -EINVAL; + device->driver_data = NULL; + if (state.next_uuid) + acpi_os_unmap_memory(state.next_uuid, sizeof(*state.next_uuid)); + state.next_uuid = NULL; + return 0; +} + +static void vmgenid_acpi_notify(struct acpi_device *device, u32 event) +{ + uuid_t old_uuid; + + if (!device || acpi_driver_data(device) != &state) + return; + old_uuid = state.this_uuid; + state.this_uuid = *state.next_uuid; + if (!memcmp(&old_uuid, &state.this_uuid, sizeof(state.this_uuid))) + return; + add_vmfork_randomness(&state.this_uuid, sizeof(state.this_uuid)); +} + +static const struct acpi_device_id vmgenid_ids[] = { + {"VMGENID", 0}, + {"QEMUVGID", 0}, + { }, +}; + +static struct acpi_driver acpi_driver = { + .name = "vm_generation_id", + .ids = vmgenid_ids, + .owner = THIS_MODULE, + .ops = { + .add = vmgenid_acpi_add, + .remove = vmgenid_acpi_remove, + .notify = vmgenid_acpi_notify, + } +}; + +static int __init vmgenid_init(void) +{ + return acpi_bus_register_driver(&acpi_driver); +} + +static void __exit vmgenid_exit(void) +{ + acpi_bus_unregister_driver(&acpi_driver); +} + +module_init(vmgenid_init); +module_exit(vmgenid_exit); + +MODULE_DEVICE_TABLE(acpi, vmgenid_ids); +MODULE_DESCRIPTION("Virtual Machine Generation ID"); +MODULE_LICENSE("GPL v2");