From patchwork Tue Mar 15 23:00:35 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nathan Huckleberry X-Patchwork-Id: 12781946 X-Patchwork-Delegate: herbert@gondor.apana.org.au 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 8AC60C433EF for ; Tue, 15 Mar 2022 23:01:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352486AbiCOXCX (ORCPT ); Tue, 15 Mar 2022 19:02:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55242 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352470AbiCOXCU (ORCPT ); Tue, 15 Mar 2022 19:02:20 -0400 Received: from mail-ua1-x94a.google.com (mail-ua1-x94a.google.com [IPv6:2607:f8b0:4864:20::94a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1F5915DA43 for ; Tue, 15 Mar 2022 16:01:05 -0700 (PDT) Received: by mail-ua1-x94a.google.com with SMTP id f15-20020ab032cf000000b0034a3f7989bbso246517uao.18 for ; Tue, 15 Mar 2022 16:01:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=suaKSImjwVWUKasHdAueNOcQEbe2FYBxmaL4SY3JCTA=; b=FNEzez77+s9QcMNNjdb00ZBn4WVqlQ0bPaLiJ/BciO6Ci9Q59MfEvCQWYR2lXbk2dm gL9CMWB08AFAmvQ16yZguPDnoPb3pkEDS36SW+tLpGFh6Xp2ivJXUAlJE0V5sCYAGUZg vteG940vPsPNv8pDgaoq3RzX2WzI0kIusXQbBaqvTyQKDarKnwxz383lv12mKt+XQsLF mreOg19yfHGLQSOE+qp1CfF6rCxlbv6zqaCyuDu4Eqny8Qj7XLULs7pe+H8NCt2cnAV7 qDPNHBYbn1Di+21wzupi2MXiNLxP+oEeDhPYUR6i2kJ86ClS4tXY4DAMy3dRS+uFbk7s lgWQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=suaKSImjwVWUKasHdAueNOcQEbe2FYBxmaL4SY3JCTA=; b=pOuO2OUkPZky0mVomXunxN2J12GS090+C7FIYNDKoS1L84bQa0q1s6hEG8kUh9cW9w ieFKKo0PrIY/FnoksE/kPPcERmEC2mSWWRHqLIDP+fCCSUYEeHzDJPl5HCKKpqcq4bVB FolMRCfavab63WSEkmREq+wRLNBNbmZbMVqAqj1orj9eAcraEjupAOWc9+ZUL50QlTMY d3gs+3SIzSL/h6plz9JcLpS+1OrbFlUjLoX/7EAd0JJS6BIKbnz1fOJqJn1BZ9Z1VXlU oAcZCPRDMBbCDsUVKr3gsSvGKdP/c4HUAikZucBIjOM31kO1NoBLJ6w+z87iHnNuxLvy YnCQ== X-Gm-Message-State: AOAM531R1cwVgPWFavPJrP609MdQD9ZeCKJI5M5bU4X3AKA/upQC+WTQ 7lB11S3dH2BmXqvGa7Ww5rBpppbdPyRwc+BtA8wxHWOonfvwKzfeqXHbkbTrovSBe3cK4wfb0Rf 9HFL9vRDwjzXN+izoyBzcdiEMBC0TEiW5GCgrQujN1Obq8A1tpcTM61lA/bGzWNwd72s= X-Google-Smtp-Source: ABdhPJw3hHrikig2O1QCkQsJ1/YMtfNG2lAXtLPx2ZrYR6CJsQLijLwqqF0LioOrVCcPgBAc+U6ri7y40g== X-Received: from nhuck.c.googlers.com ([fda3:e722:ac3:cc00:14:4d90:c0a8:39cc]) (user=nhuck job=sendgmr) by 2002:a05:6122:8ca:b0:332:64b4:8109 with SMTP id 10-20020a05612208ca00b0033264b48109mr12954628vkg.7.1647385264152; Tue, 15 Mar 2022 16:01:04 -0700 (PDT) Date: Tue, 15 Mar 2022 23:00:35 +0000 In-Reply-To: <20220315230035.3792663-1-nhuck@google.com> Message-Id: <20220315230035.3792663-9-nhuck@google.com> Mime-Version: 1.0 References: <20220315230035.3792663-1-nhuck@google.com> X-Mailer: git-send-email 2.35.1.723.g4982287a31-goog Subject: [PATCH v3 8/8] fscrypt: Add HCTR2 support for filename encryption From: Nathan Huckleberry To: linux-crypto@vger.kernel.org Cc: Herbert Xu , "David S. Miller" , linux-arm-kernel@lists.infradead.org, Paul Crowley , Eric Biggers , Sami Tolvanen , Ard Biesheuvel , Nathan Huckleberry Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org HCTR2 is a tweakable, length-preserving encryption mode. It has the same security guarantees as Adiantum, but is intended for use on CPUs with dedicated crypto instructions. It fixes a known weakness with filename encryption: when two filenames in the same directory share a prefix of >= 16 bytes, with CTS-CBC their encrypted filenames share a common substring, leaking information. HCTR2 does not have this problem. More information on HCTR2 can be found here: Length-preserving encryption with HCTR2: https://eprint.iacr.org/2021/1441.pdf Signed-off-by: Nathan Huckleberry --- Documentation/filesystems/fscrypt.rst | 19 ++++++++++++++----- fs/crypto/fscrypt_private.h | 2 +- fs/crypto/keysetup.c | 7 +++++++ fs/crypto/policy.c | 4 ++++ include/uapi/linux/fscrypt.h | 3 ++- tools/include/uapi/linux/fscrypt.h | 3 ++- 6 files changed, 30 insertions(+), 8 deletions(-) diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 4d5d50dca65c..09915086abd8 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -337,6 +337,7 @@ Currently, the following pairs of encryption modes are supported: - AES-256-XTS for contents and AES-256-CTS-CBC for filenames - AES-128-CBC for contents and AES-128-CTS-CBC for filenames - Adiantum for both contents and filenames +- AES-256-XTS for contents and AES-256-HCTR2 for filenames If unsure, you should use the (AES-256-XTS, AES-256-CTS-CBC) pair. @@ -357,6 +358,14 @@ To use Adiantum, CONFIG_CRYPTO_ADIANTUM must be enabled. Also, fast implementations of ChaCha and NHPoly1305 should be enabled, e.g. CONFIG_CRYPTO_CHACHA20_NEON and CONFIG_CRYPTO_NHPOLY1305_NEON for ARM. +AES-256-HCTR2 is another true wide-block encryption mode. It has the same +security guarantees as Adiantum, but is intended for use on CPUs with dedicated +crypto instructions. See the paper "Length-preserving encryption with HCTR2" +(https://eprint.iacr.org/2021/1441.pdf) for more details. To use HCTR2, +CONFIG_CRYPTO_HCTR2 must be enabled. Also, fast implementations of XCTR and +POLYVAL should be enabled, e.g. CRYPTO_POLYVAL_ARM64_CE and +CRYPTO_AES_ARM64_CE_BLK for ARM64. + New encryption modes can be added relatively easily, without changes to individual filesystems. However, authenticated encryption (AE) modes are not currently supported because of the difficulty of dealing @@ -404,11 +413,11 @@ alternatively has the file's nonce (for `DIRECT_KEY policies`_) or inode number (for `IV_INO_LBLK_64 policies`_) included in the IVs. Thus, IV reuse is limited to within a single directory. -With CTS-CBC, the IV reuse means that when the plaintext filenames -share a common prefix at least as long as the cipher block size (16 -bytes for AES), the corresponding encrypted filenames will also share -a common prefix. This is undesirable. Adiantum does not have this -weakness, as it is a wide-block encryption mode. +With CTS-CBC, the IV reuse means that when the plaintext filenames share a +common prefix at least as long as the cipher block size (16 bytes for AES), the +corresponding encrypted filenames will also share a common prefix. This is +undesirable. Adiantum and HCTR2 do not have this weakness, as they are +wide-block encryption modes. All supported filenames encryption modes accept any plaintext length >= 16 bytes; cipher block alignment is not required. However, diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h index 5b0a9e6478b5..d8617d01f7bd 100644 --- a/fs/crypto/fscrypt_private.h +++ b/fs/crypto/fscrypt_private.h @@ -31,7 +31,7 @@ #define FSCRYPT_CONTEXT_V2 2 /* Keep this in sync with include/uapi/linux/fscrypt.h */ -#define FSCRYPT_MODE_MAX FSCRYPT_MODE_ADIANTUM +#define FSCRYPT_MODE_MAX FSCRYPT_MODE_AES_256_HCTR2 struct fscrypt_context_v1 { u8 version; /* FSCRYPT_CONTEXT_V1 */ diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c index eede186b04ce..ae24b581d3d7 100644 --- a/fs/crypto/keysetup.c +++ b/fs/crypto/keysetup.c @@ -53,6 +53,13 @@ struct fscrypt_mode fscrypt_modes[] = { .ivsize = 32, .blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM, }, + [FSCRYPT_MODE_AES_256_HCTR2] = { + .friendly_name = "HCTR2", + .cipher_str = "hctr2(aes)", + .keysize = 32, + .security_strength = 32, + .ivsize = 32, + }, }; static DEFINE_MUTEX(fscrypt_mode_key_setup_mutex); diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c index ed3d623724cd..fa8bdb8c76b7 100644 --- a/fs/crypto/policy.c +++ b/fs/crypto/policy.c @@ -54,6 +54,10 @@ static bool fscrypt_valid_enc_modes(u32 contents_mode, u32 filenames_mode) filenames_mode == FSCRYPT_MODE_ADIANTUM) return true; + if (contents_mode == FSCRYPT_MODE_AES_256_XTS && + filenames_mode == FSCRYPT_MODE_AES_256_HCTR2) + return true; + return false; } diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h index 9f4428be3e36..a756b29afcc2 100644 --- a/include/uapi/linux/fscrypt.h +++ b/include/uapi/linux/fscrypt.h @@ -27,7 +27,8 @@ #define FSCRYPT_MODE_AES_128_CBC 5 #define FSCRYPT_MODE_AES_128_CTS 6 #define FSCRYPT_MODE_ADIANTUM 9 -/* If adding a mode number > 9, update FSCRYPT_MODE_MAX in fscrypt_private.h */ +#define FSCRYPT_MODE_AES_256_HCTR2 10 +/* If adding a mode number > 10, update FSCRYPT_MODE_MAX in fscrypt_private.h */ /* * Legacy policy version; ad-hoc KDF and no key verification. diff --git a/tools/include/uapi/linux/fscrypt.h b/tools/include/uapi/linux/fscrypt.h index 9f4428be3e36..a756b29afcc2 100644 --- a/tools/include/uapi/linux/fscrypt.h +++ b/tools/include/uapi/linux/fscrypt.h @@ -27,7 +27,8 @@ #define FSCRYPT_MODE_AES_128_CBC 5 #define FSCRYPT_MODE_AES_128_CTS 6 #define FSCRYPT_MODE_ADIANTUM 9 -/* If adding a mode number > 9, update FSCRYPT_MODE_MAX in fscrypt_private.h */ +#define FSCRYPT_MODE_AES_256_HCTR2 10 +/* If adding a mode number > 10, update FSCRYPT_MODE_MAX in fscrypt_private.h */ /* * Legacy policy version; ad-hoc KDF and no key verification.