On Thu, Jun 20, 2019 at 11:15:05AM -0700, Eric Biggers wrote: > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > 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. > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> > --- > 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 08c23b60e01647..87d4e266ffc86d 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 24ed99e2eca0b2..5fdf24877c1785 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 > -- > 2.22.0.410.gd8fdbe21b5-goog > Applied to fscrypt.git for v5.3. - Eric
