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-rw-r--r--Documentation/filesystems/fscrypt.rst43
1 files changed, 42 insertions, 1 deletions
diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index 08c23b60e016..82efa41b0e6c 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
@@ -647,3 +649,42 @@ Note that the precise way that filenames are presented to userspace
without the key is subject to change in the future. It is only meant
as a way to temporarily present valid filenames so that commands like
``rm -r`` work as expected on encrypted directories.
+
+Tests
+=====
+
+To test fscrypt, use xfstests, which is Linux's de facto standard
+filesystem test suite. First, run all the tests in the "encrypt"
+group on the relevant filesystem(s). For example, to test ext4 and
+f2fs encryption using `kvm-xfstests
+<https://github.com/tytso/xfstests-bld/blob/master/Documentation/kvm-quickstart.md>`_::
+
+ kvm-xfstests -c ext4,f2fs -g encrypt
+
+UBIFS encryption can also be tested this way, but it should be done in
+a separate command, and it takes some time for kvm-xfstests to set up
+emulated UBI volumes::
+
+ kvm-xfstests -c ubifs -g encrypt
+
+No tests should fail. However, tests that use non-default encryption
+modes (e.g. generic/549 and generic/550) will be skipped if the needed
+algorithms were not built into the kernel's crypto API. Also, tests
+that access the raw block device (e.g. generic/399, generic/548,
+generic/549, generic/550) will be skipped on UBIFS.
+
+Besides running the "encrypt" group tests, for ext4 and f2fs it's also
+possible to run most xfstests with the "test_dummy_encryption" mount
+option. This option causes all new files to be automatically
+encrypted with a dummy key, without having to make any API calls.
+This tests the encrypted I/O paths more thoroughly. To do this with
+kvm-xfstests, use the "encrypt" filesystem configuration::
+
+ kvm-xfstests -c ext4/encrypt,f2fs/encrypt -g auto
+
+Because this runs many more tests than "-g encrypt" does, it takes
+much longer to run; so also consider using `gce-xfstests
+<https://github.com/tytso/xfstests-bld/blob/master/Documentation/gce-xfstests.md>`_
+instead of kvm-xfstests::
+
+ gce-xfstests -c ext4/encrypt,f2fs/encrypt -g auto