From patchwork Thu Nov 3 18:01:08 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Evan Green X-Patchwork-Id: 13030775 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 747A5C4332F for ; Thu, 3 Nov 2022 18:04:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231197AbiKCSEM (ORCPT ); Thu, 3 Nov 2022 14:04:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40890 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230337AbiKCSD5 (ORCPT ); Thu, 3 Nov 2022 14:03:57 -0400 Received: from mail-pj1-x1029.google.com (mail-pj1-x1029.google.com [IPv6:2607:f8b0:4864:20::1029]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B91452314B for ; Thu, 3 Nov 2022 11:01:36 -0700 (PDT) Received: by mail-pj1-x1029.google.com with SMTP id v4-20020a17090a088400b00212cb0ed97eso2526565pjc.5 for ; Thu, 03 Nov 2022 11:01:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=we5sGRgeZfmiFwJlXRzMaUU1kYxW1X5nCMITmEl34Rs=; b=Kq6Bj/FL8nuh60ks1BQiKahd6V4pWny3fxV6iEgxy2pFv78eAfevsv4OJyz5VsL+ht rm3NW/7+kbgnxI4es0cLSJvuSAte0IIlpsjaygXTHiwMOMjBXV3o4DpY7nh/rjv5+9zK hLF3Azra8sUrIvaGsQ0ceLKhAQIYeDsvvKFGo= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=we5sGRgeZfmiFwJlXRzMaUU1kYxW1X5nCMITmEl34Rs=; b=kgBDXhyzIW3X8vFsfXYM3FBYuZRWzxR1AB+TAv/4fZOxtQ2o9znITxKQktv5wlVVPQ SqUQ3rW4NjlsRk8DETNloNai8aa8QVO/PrH6D/egMmYSxkdpg5TmeLb1msu1WMYMWk1G OCJ39/iKmLfaiLgBCV8SBJhuWEZPDP36WH017O9OfJj0MkxugMEpkOGrCY2r5ZEkZ5zC 4nNMjL081nHrv7hzNbYoi1HOrogUM+bZiN5XATUH0wPnHCz93RMCf4QqL8QmkyyODi8k 1w21TS5Jiv0rtpiiI7yNhfIywGSvHvZgb6nCUrTCDL96lrBQQ4vXRtc6SHE3Kt0r+9cl MlKA== X-Gm-Message-State: ACrzQf1xnKzYz8TYJMkSnPqLkQkJwNAoPZs+ezUP6U6mo62FYZaaJiz6 HJ9cW/zeoiuUcqK9RuqqPvkQ3A== X-Google-Smtp-Source: AMsMyM6pJ+WHoxy7JrmybugEwNm3RYa+8+Uvc7wfkCiQEh8cdwxjvdHYYa4Krbf8KHv6hakd6k78Fw== X-Received: by 2002:a17:90a:4a0f:b0:213:f398:ed20 with SMTP id e15-20020a17090a4a0f00b00213f398ed20mr20866017pjh.110.1667498496170; Thu, 03 Nov 2022 11:01:36 -0700 (PDT) Received: from evgreen-glaptop.lan ([98.45.28.95]) by smtp.gmail.com with ESMTPSA id t12-20020a1709027fcc00b00177fb862a87sm1000277plb.20.2022.11.03.11.01.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Nov 2022 11:01:35 -0700 (PDT) From: Evan Green To: linux-kernel@vger.kernel.org Cc: corbet@lwn.net, linux-pm@vger.kernel.org, rjw@rjwysocki.net, gwendal@chromium.org, apronin@chromium.org, Pavel Machek , Kees Cook , Matthew Garrett , linux-integrity@vger.kernel.org, jejb@linux.ibm.com, zohar@linux.ibm.com, dlunev@google.com, Eric Biggers , Ben Boeckel , jarkko@kernel.org, Evan Green , David Howells , James Morris , Jason Gunthorpe , Len Brown , Matthew Garrett , Paul Moore , Peter Huewe , "Rafael J. Wysocki" , "Serge E. Hallyn" , axelj , keyrings@vger.kernel.org, linux-doc@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH v4 00/11] Encrypted Hibernation Date: Thu, 3 Nov 2022 11:01:08 -0700 Message-Id: <20221103180120.752659-1-evgreen@chromium.org> X-Mailer: git-send-email 2.38.1.431.g37b22c650d-goog MIME-Version: 1.0 Precedence: bulk List-ID: We are exploring enabling hibernation in some new scenarios. However, our security team has a few requirements, listed below: 1. The hibernate image must be encrypted with protection derived from both the platform (eg TPM) and user authentication data (eg password). 2. Hibernation must not be a vector by which a malicious userspace can escalate to the kernel. Requirement #1 can be achieved solely with uswsusp, however requirement 2 necessitates mechanisms in the kernel to guarantee integrity of the hibernate image. The kernel needs a way to authenticate that it generated the hibernate image being loaded, and that the image has not been tampered with. Adding support for in-kernel AEAD encryption with a TPM-sealed key allows us to achieve both requirements with a single computation pass. Matthew Garrett published a series [1] that aligns closely with this goal. His series utilized the fact that PCR23 is a resettable PCR that can be blocked from access by usermode. The TPM can create a sealed key tied to PCR23 in two ways. First, the TPM can attest to the value of PCR23 when the key was created, which the kernel can use on resume to verify that the kernel must have created the key (since it is the only one capable of modifying PCR23). It can also create a policy that enforces PCR23 be set to a specific value as a condition of unsealing the key, preventing usermode from unsealing the key by talking directly to the TPM. This series adopts that primitive as a foundation, tweaking and building on it a bit. Where Matthew's series used the TPM-backed key to encrypt a hash of the image, this series uses the key directly as a gcm(aes) encryption key, which the kernel uses to encrypt and decrypt the hibernate image in chunks of 16 pages. This provides both encryption and integrity, which turns out to be a noticeable performance improvement over separate passes for encryption and hashing. The series also introduces the concept of mixing user key material into the encryption key. This allows usermode to introduce key material based on unspecified external authentication data (in our case derived from something like the user password or PIN), without requiring usermode to do a separate encryption pass. Matthew also documented issues his series had [2] related to generating fake images by booting alternate kernels without the PCR23 limiting. With access to PCR23 on the same machine, usermode can create fake hibernate images that are indistinguishable to the new kernel from genuine ones. His post outlines a solution that involves adding more PCRs into the creation data and policy, with some gyrations to make this work well on a standard PC. Our approach would be similar: on our machines PCR 0 indicates whether the system is booted in secure/verified mode or developer mode. By adding PCR0 to the policy, we can reject hibernate images made in developer mode while in verified mode (or vice versa). Additionally, mixing in the user authentication data limits both data exfiltration attacks (eg a stolen laptop) and forged hibernation image attacks to attackers that already know the authentication data (eg user's password). This, combined with our relatively sealed userspace (dm-verity on the rootfs), and some judicious clearing of the hibernate image (such as across an OS update) further reduce the risk of an online attack. The remaining attack space of a forgery from someone with physical access to the device and knowledge of the authentication data is out of scope for us, given that flipping to developer mode or reflashing RO firmware trivially achieves the same thing. A couple of patches still need to be written on top of this series. The generalized functionality to OR in additional PCRs via Kconfig (like PCR 0 or 5) still needs to be added. We'll also need a patch that disallows unencrypted forms of resume from hibernation, to fully close the door to malicious userspace. However, I wanted to get this series out first and get reactions from upstream before continuing to add to it. [1] https://patchwork.kernel.org/project/linux-pm/cover/20210220013255.1083202-1-matthewgarrett@google.com/ [2] https://mjg59.dreamwidth.org/58077.html Changes in v4: - Open code tpm2_pcr_reset implementation in tpm-interface.c (Jarkko) - Rename interface symbol to tpm2_pcr_reset, fix kerneldocs (Jarkko) - Augment the commit message (Jarkko) - Local ordering and whitespace changes (Jarkko) - s/tpm_pcr_reset/tpm2_pcr_reset/ due to change in other patch - Variable ordering and whitespace fixes (Jarkko) - Add NULL check explanation in teardown (Jarkko) - Change strlen+1 to sizeof for static buffer (Jarkko) - Fix nr_allocated_banks loop overflow (found via KASAN) - Local variable reordering (Jarkko) - Local variable ordering (Jarkko) Changes in v3: - Unify tpm1/2_pcr_reset prototypes (Jarkko) - Wait no, remove the TPM1 stuff altogether (Jarkko) - Remove extra From tag and blank in commit msg (Jarkko). - Split find_and_validate_cc() export to its own patch (Jarkko) - Rename tpm_find_and_validate_cc() to tpm2_find_and_validate_cc(). - Fix up commit message (Jarkko) - tpm2_find_and_validate_cc() was split (Jarkko) - Simply fully restrict TPM1 since v2 failed to account for tunnelled transport sessions (Stefan and Jarkko). - Fix SoB and -- note ordering (Kees) - Add comments describing the TPM2 spec type names for the new fields in tpm2key.asn1 (Kees) - Add len buffer checks in tpm2_key_encode() (Kees) - Clarified creationpcrs documentation (Ben) - Changed funky tag to suggested-by (Kees). Matthew, holler if you want something different. - ENCRYPTED_HIBERNATION needs TRUSTED_KEYS builtin for key_type_trusted. - Remove KEYS dependency since it's covered by TRUSTED_KEYS (Kees) - Changed funky tag to Co-developed-by (Kees). Matthew, holler if you want something different. - Changed funky tag to Co-developed-by (Kees) Changes in v2: - Fixed sparse warnings - Adjust hash len by 2 due to new ASN.1 storage, and add underflow check. - Rework load/create_kernel_key() to eliminate a label (Andrey) - Call put_device() needed from calling tpm_default_chip(). - Add missing static on snapshot_encrypted_byte_count() - Fold in only the used kernel key bytes to the user key. - Make the user key length 32 (Eric) - Use CRYPTO_LIB_SHA256 for less boilerplate (Eric) - Fixed some sparse warnings - Use CRYPTO_LIB_SHA256 to get rid of sha256_data() (Eric) - Adjusted offsets due to new ASN.1 format, and added a creation data length check. - Fix sparse warnings - Fix session type comment (Andrey) - Eliminate extra label in get/create_kernel_key() (Andrey) - Call tpm_try_get_ops() before calling tpm2_flush_context(). Evan Green (8): tpm: Export and rename tpm2_find_and_validate_cc() security: keys: trusted: Include TPM2 creation data security: keys: trusted: Verify creation data PM: hibernate: Add kernel-based encryption PM: hibernate: Use TPM-backed keys to encrypt image PM: hibernate: Mix user key in encrypted hibernate PM: hibernate: Verify the digest encryption key PM: hibernate: seal the encryption key with a PCR policy Matthew Garrett (3): tpm: Add support for in-kernel resetting of PCRs tpm: Allow PCR 23 to be restricted to kernel-only use security: keys: trusted: Allow storage of PCR values in creation data Documentation/power/userland-swsusp.rst | 8 + .../security/keys/trusted-encrypted.rst | 6 + drivers/char/tpm/Kconfig | 12 + drivers/char/tpm/tpm-dev-common.c | 8 + drivers/char/tpm/tpm-interface.c | 47 + drivers/char/tpm/tpm.h | 22 + drivers/char/tpm/tpm1-cmd.c | 13 + drivers/char/tpm/tpm2-cmd.c | 29 +- drivers/char/tpm/tpm2-space.c | 8 +- include/keys/trusted-type.h | 9 + include/linux/tpm.h | 19 + include/uapi/linux/suspend_ioctls.h | 28 +- kernel/power/Kconfig | 15 + kernel/power/Makefile | 1 + kernel/power/power.h | 1 + kernel/power/snapenc.c | 1043 +++++++++++++++++ kernel/power/snapshot.c | 5 + kernel/power/user.c | 44 +- kernel/power/user.h | 116 ++ security/keys/trusted-keys/tpm2key.asn1 | 15 +- security/keys/trusted-keys/trusted_tpm1.c | 9 + security/keys/trusted-keys/trusted_tpm2.c | 318 ++++- 22 files changed, 1724 insertions(+), 52 deletions(-) create mode 100644 kernel/power/snapenc.c create mode 100644 kernel/power/user.h