From adbd9b4dee70c36eaa30ce93ffcd968533044efc Mon Sep 17 00:00:00 2001 From: Eric Biggers <ebiggers@google.com> Date: Thu, 20 Jun 2019 11:15:05 -0700 Subject: [PATCH] fscrypt: remove selection of CONFIG_CRYPTO_SHA256 fscrypt only uses SHA-256 for AES-128-CBC-ESSIV, which isn't the default and is only recommended on platforms that have hardware accelerated AES-CBC but not AES-XTS. There's no link-time dependency, since SHA-256 is requested via the crypto API on first use. To reduce bloat, we should limit FS_ENCRYPTION to selecting the default algorithms only. SHA-256 by itself isn't that much bloat, but it's being discussed to move ESSIV into a crypto API template, which would incidentally bring in other things like "authenc" support, which would all end up being built-in since FS_ENCRYPTION is now a bool. For Adiantum encryption we already just document that users who want to use it have to enable CONFIG_CRYPTO_ADIANTUM themselves. So, let's do the same for AES-128-CBC-ESSIV and CONFIG_CRYPTO_SHA256. Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Eric Biggers <ebiggers@google.com> --- Documentation/filesystems/fscrypt.rst | 4 +++- fs/crypto/Kconfig | 1 - 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 08c23b60e016..87d4e266ffc8 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -191,7 +191,9 @@ Currently, the following pairs of encryption modes are supported: If unsure, you should use the (AES-256-XTS, AES-256-CTS-CBC) pair. AES-128-CBC was added only for low-powered embedded devices with -crypto accelerators such as CAAM or CESA that do not support XTS. +crypto accelerators such as CAAM or CESA that do not support XTS. To +use AES-128-CBC, CONFIG_CRYPTO_SHA256 (or another SHA-256 +implementation) must be enabled so that ESSIV can be used. Adiantum is a (primarily) stream cipher-based mode that is fast even on CPUs without dedicated crypto instructions. It's also a true diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig index 24ed99e2eca0..5fdf24877c17 100644 --- a/fs/crypto/Kconfig +++ b/fs/crypto/Kconfig @@ -7,7 +7,6 @@ config FS_ENCRYPTION select CRYPTO_ECB select CRYPTO_XTS select CRYPTO_CTS - select CRYPTO_SHA256 select KEYS help Enable encryption of files and directories. This -- 2.30.9