From patchwork Fri May 20 18:15:01 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nathan Huckleberry X-Patchwork-Id: 12857090 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 8ACAFC4167B for ; Fri, 20 May 2022 18:15:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352541AbiETSPv (ORCPT ); Fri, 20 May 2022 14:15:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39746 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352515AbiETSPp (ORCPT ); Fri, 20 May 2022 14:15:45 -0400 Received: from mail-yw1-x114a.google.com (mail-yw1-x114a.google.com [IPv6:2607:f8b0:4864:20::114a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8FF9A190D06 for ; Fri, 20 May 2022 11:15:21 -0700 (PDT) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-2fefb9975c5so77497687b3.21 for ; Fri, 20 May 2022 11:15:21 -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=YshN7hPCL90ouCwH043GJCNcmwyKXc05g8b5XDVe1V8=; b=cHk2E2hxbPk39aFSReNHJ2es01aqwP27rmUBSzchsoKGT5fB0FvE89cBE5xN9CTgat 4AC7wf6PbIn0wNpd531om/aDoFRcZlrRiNwmeq2VL8eYXJ18IbCO2kZNPXoDPqTQTOs0 SBF2ci8daEarIdkn94/UnwdsBK3/4pJrqs0+8KMTJl66ei8Q2u0QZu321b6aowFzBMEy sZmvEcgM9GQY+fTP7LAAlgy6DZ2kFeZLUpeerNBrvlHMHMFxOSVP8UnrL2tCYsjfgC67 g6+VJzqG2OxsuqmK7pxe+zonbs2et9ncASn4GbfV8/P2rAq3pc4yqqjS+VyeymC51EVq U5Nw== 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=YshN7hPCL90ouCwH043GJCNcmwyKXc05g8b5XDVe1V8=; b=ISqBWr4/ZbDoOWAYkdn3awrcU245VvTsreL1lk2T1TxjoeNjlUMgDBVQpL4Mi7z7ST WF30kk6LH6nadfRAcSXxjIjuiN/CgeBaBp9YjqUWAFP1+5clMNmpdNVaCLqbe4+eFu1h cNPcng82Dbq8CHDL+lidtNf6PdFPou6ViI38zsarSyWxmfJa1fs6CQHRTXHsvx6cvZpw +4HWjqj3fKmM1PDu4jxLaef+uXVSnc95psnGqEdgPhjSceAGO1IgDuj+tUIQ9JLEElcl 5EfTIU8U/CYsG5ekEA0yno1BGChWf7FioQy7GKWu4GV3lkQJ7JqbJvMgT5OsGNYmVoWI PD3Q== X-Gm-Message-State: AOAM530TUY5rXxriDwTnkhwcHUIezM6jDrfmVZ0SgfGsroZkmE+HmMYr NN3gvij+/mU34dqYSffDIm8IBT7VrQ== X-Google-Smtp-Source: ABdhPJwdQ+wuFJ9ns8qEfyi7qaVYdS0KOp0jYFOzS2drzsK549+jhbId2mJLkhLqGnNVBAzGsg8U80ZmEw== X-Received: from nhuck.c.googlers.com ([fda3:e722:ac3:cc00:14:4d90:c0a8:39cc]) (user=nhuck job=sendgmr) by 2002:a25:6d5:0:b0:64a:c36e:8bff with SMTP id 204-20020a2506d5000000b0064ac36e8bffmr10416026ybg.121.1653070520788; Fri, 20 May 2022 11:15:20 -0700 (PDT) Date: Fri, 20 May 2022 18:15:01 +0000 In-Reply-To: <20220520181501.2159644-1-nhuck@google.com> Message-Id: <20220520181501.2159644-10-nhuck@google.com> Mime-Version: 1.0 References: <20220520181501.2159644-1-nhuck@google.com> X-Mailer: git-send-email 2.36.1.124.g0e6072fb45-goog Subject: [PATCH v9 9/9] fscrypt: Add HCTR2 support for filename encryption From: Nathan Huckleberry To: linux-crypto@vger.kernel.org Cc: linux-fscrypt@vger.kernel.org, Herbert Xu , "David S. Miller" , linux-arm-kernel@lists.infradead.org, Paul Crowley , Eric Biggers , Sami Tolvanen , Ard Biesheuvel , Nathan Huckleberry , Eric Biggers Precedence: bulk List-ID: X-Mailing-List: linux-fscrypt@vger.kernel.org HCTR2 is a tweakable, length-preserving encryption mode that is intended for use on CPUs with dedicated crypto instructions. HCTR2 has the property that a bitflip in the plaintext changes the entire ciphertext. This property fixes a known weakness with filename encryption: when two filenames in the same directory share a prefix of >= 16 bytes, with AES-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 Reviewed-by: Ard Biesheuvel Acked-by: Eric Biggers --- Documentation/filesystems/fscrypt.rst | 22 +++++++++++++++++----- fs/crypto/fscrypt_private.h | 2 +- fs/crypto/keysetup.c | 7 +++++++ fs/crypto/policy.c | 14 +++++++++++--- include/uapi/linux/fscrypt.h | 3 ++- 5 files changed, 38 insertions(+), 10 deletions(-) diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 4d5d50dca65c..324149c58bf3 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 (v2 policies only) If unsure, you should use the (AES-256-XTS, AES-256-CTS-CBC) pair. @@ -357,6 +358,17 @@ 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 that is intended for +use on CPUs with dedicated crypto instructions. AES-256-HCTR2 has the property +that a bitflip in the plaintext changes the entire ciphertext. This property +makes it desirable for filename encryption since initialization vectors are +reused within a directory. For more details on AES-256-HCTR2, see the paper +"Length-preserving encryption with HCTR2" +(https://eprint.iacr.org/2021/1441.pdf). To use AES-256-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 +416,11 @@ 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..ba463eb931de 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 = "AES-256-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..5dea7b655a64 100644 --- a/fs/crypto/policy.c +++ b/fs/crypto/policy.c @@ -40,7 +40,7 @@ fscrypt_get_dummy_policy(struct super_block *sb) return sb->s_cop->get_dummy_policy(sb); } -static bool fscrypt_valid_enc_modes(u32 contents_mode, u32 filenames_mode) +static bool fscrypt_valid_enc_modes_v1(u32 contents_mode, u32 filenames_mode) { if (contents_mode == FSCRYPT_MODE_AES_256_XTS && filenames_mode == FSCRYPT_MODE_AES_256_CTS) @@ -57,6 +57,14 @@ static bool fscrypt_valid_enc_modes(u32 contents_mode, u32 filenames_mode) return false; } +static bool fscrypt_valid_enc_modes_v2(u32 contents_mode, u32 filenames_mode) +{ + if (contents_mode == FSCRYPT_MODE_AES_256_XTS && + filenames_mode == FSCRYPT_MODE_AES_256_HCTR2) + return true; + return fscrypt_valid_enc_modes_v1(contents_mode, filenames_mode); +} + static bool supported_direct_key_modes(const struct inode *inode, u32 contents_mode, u32 filenames_mode) { @@ -130,7 +138,7 @@ static bool supported_iv_ino_lblk_policy(const struct fscrypt_policy_v2 *policy, static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy, const struct inode *inode) { - if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode, + if (!fscrypt_valid_enc_modes_v1(policy->contents_encryption_mode, policy->filenames_encryption_mode)) { fscrypt_warn(inode, "Unsupported encryption modes (contents %d, filenames %d)", @@ -166,7 +174,7 @@ static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy, { int count = 0; - if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode, + if (!fscrypt_valid_enc_modes_v2(policy->contents_encryption_mode, policy->filenames_encryption_mode)) { fscrypt_warn(inode, "Unsupported encryption modes (contents %d, filenames %d)", 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.