* [PATCH v2 1/2] docs: kdoc: Expand 'at_least' when creating parameter list
2026-04-18 19:21 [PATCH v2 0/2] Improve the crypto library documentation Eric Biggers
@ 2026-04-18 19:21 ` Eric Biggers
2026-04-18 23:50 ` Randy Dunlap
2026-04-18 19:21 ` [PATCH v2 2/2] lib/crypto: docs: Add rst documentation to Documentation/crypto/ Eric Biggers
1 sibling, 1 reply; 5+ messages in thread
From: Eric Biggers @ 2026-04-18 19:21 UTC (permalink / raw)
To: linux-crypto
Cc: linux-kernel, Ard Biesheuvel, Jason A . Donenfeld, Herbert Xu,
linux-doc, Jonathan Corbet, Mauro Carvalho Chehab, Randy Dunlap,
Eric Biggers
sphinx doesn't know that the kernel headers do:
#define at_least static
Do this replacement before declarations are passed to it.
This prevents errors like the following from appearing once the
lib/crypto/ kernel-doc is wired up to the sphinx build:
linux/Documentation/crypto/libcrypto:128: ./include/crypto/sha2.h:773: WARNING: Error in declarator or parameters
Error in declarator or parameters
Invalid C declaration: Expected ']' in end of array operator. [error at 59]
void sha512_final (struct sha512_ctx *ctx, u8 out[at_least SHA512_DIGEST_SIZE])
Acked-by: Jonathan Corbet <corbet@lwn.net>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
tools/lib/python/kdoc/kdoc_parser.py | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/tools/lib/python/kdoc/kdoc_parser.py b/tools/lib/python/kdoc/kdoc_parser.py
index 74af7ae47aa47..c3f966da533e0 100644
--- a/tools/lib/python/kdoc/kdoc_parser.py
+++ b/tools/lib/python/kdoc/kdoc_parser.py
@@ -437,10 +437,15 @@ class KernelDoc:
for arg in args.split(splitter):
# Ignore argument attributes
arg = KernRe(r'\sPOS0?\s').sub(' ', arg)
+ # Replace '[at_least ' with '[static '. This allows sphinx to parse
+ # array parameter declarations like 'char A[at_least 4]', where
+ # 'at_least' is #defined to 'static' by the kernel headers.
+ arg = arg.replace('[at_least ', '[static ')
+
# Strip leading/trailing spaces
arg = arg.strip()
arg = KernRe(r'\s+').sub(' ', arg, count=1)
if arg.startswith('#'):
--
2.53.0
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH v2 2/2] lib/crypto: docs: Add rst documentation to Documentation/crypto/
2026-04-18 19:21 [PATCH v2 0/2] Improve the crypto library documentation Eric Biggers
2026-04-18 19:21 ` [PATCH v2 1/2] docs: kdoc: Expand 'at_least' when creating parameter list Eric Biggers
@ 2026-04-18 19:21 ` Eric Biggers
2026-04-18 23:52 ` Randy Dunlap
1 sibling, 1 reply; 5+ messages in thread
From: Eric Biggers @ 2026-04-18 19:21 UTC (permalink / raw)
To: linux-crypto
Cc: linux-kernel, Ard Biesheuvel, Jason A . Donenfeld, Herbert Xu,
linux-doc, Jonathan Corbet, Mauro Carvalho Chehab, Randy Dunlap,
Eric Biggers
Add a documentation file Documentation/crypto/libcrypto.rst which
provides a high-level overview of lib/crypto/.
Also add several sub-pages which include the kernel-doc for the
algorithms that have it. This makes the existing, quite extensive
kernel-doc start being included in the HTML and PDF documentation.
Note that the intent is very much *not* that everyone has to read these
Documentation/ files. The library is intended to be straightforward and
use familiar conventions; generally it should be possible to dive right
into the kernel-doc. You shouldn't need to read a lot of documentation
to just call `sha256()`, for example, or to run the unit tests if you're
already familiar with KUnit. (This differs from the traditional crypto
API which has a larger barrier to entry.)
Nevertheless, this seems worth adding. Hopefully it is useful and makes
LWN no longer consider the library to be "meticulously undocumented".
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
Documentation/crypto/index.rst | 2 +-
.../crypto/libcrypto-blockcipher.rst | 19 ++
Documentation/crypto/libcrypto-hash.rst | 86 +++++++++
Documentation/crypto/libcrypto-signature.rst | 11 ++
Documentation/crypto/libcrypto-utils.rst | 6 +
Documentation/crypto/libcrypto.rst | 165 ++++++++++++++++++
Documentation/crypto/sha3.rst | 2 +
7 files changed, 290 insertions(+), 1 deletion(-)
create mode 100644 Documentation/crypto/libcrypto-blockcipher.rst
create mode 100644 Documentation/crypto/libcrypto-hash.rst
create mode 100644 Documentation/crypto/libcrypto-signature.rst
create mode 100644 Documentation/crypto/libcrypto-utils.rst
create mode 100644 Documentation/crypto/libcrypto.rst
diff --git a/Documentation/crypto/index.rst b/Documentation/crypto/index.rst
index 4ee667c446f99..705f186d662ba 100644
--- a/Documentation/crypto/index.rst
+++ b/Documentation/crypto/index.rst
@@ -11,10 +11,11 @@ for cryptographic use cases, as well as programming examples.
.. toctree::
:caption: Table of contents
:maxdepth: 2
+ libcrypto
intro
api-intro
architecture
async-tx-api
@@ -25,6 +26,5 @@ for cryptographic use cases, as well as programming examples.
api
api-samples
descore-readme
device_drivers/index
krb5
- sha3
diff --git a/Documentation/crypto/libcrypto-blockcipher.rst b/Documentation/crypto/libcrypto-blockcipher.rst
new file mode 100644
index 0000000000000..dd5ce2f8b5151
--- /dev/null
+++ b/Documentation/crypto/libcrypto-blockcipher.rst
@@ -0,0 +1,19 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Block ciphers
+=============
+
+AES
+---
+
+Support for the AES block cipher.
+
+.. kernel-doc:: include/crypto/aes.h
+
+DES
+---
+
+Support for the DES block cipher. This algorithm is obsolete and is supported
+only for backwards compatibility.
+
+.. kernel-doc:: include/crypto/des.h
diff --git a/Documentation/crypto/libcrypto-hash.rst b/Documentation/crypto/libcrypto-hash.rst
new file mode 100644
index 0000000000000..4248e6fdc9527
--- /dev/null
+++ b/Documentation/crypto/libcrypto-hash.rst
@@ -0,0 +1,86 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Hash functions, MACs, and XOFs
+==============================
+
+AES-CMAC and AES-XCBC-MAC
+-------------------------
+
+Support for the AES-CMAC and AES-XCBC-MAC message authentication codes.
+
+.. kernel-doc:: include/crypto/aes-cbc-macs.h
+
+BLAKE2b
+-------
+
+Support for the BLAKE2b cryptographic hash function.
+
+.. kernel-doc:: include/crypto/blake2b.h
+
+BLAKE2s
+-------
+
+Support for the BLAKE2s cryptographic hash function.
+
+.. kernel-doc:: include/crypto/blake2s.h
+
+GHASH and POLYVAL
+-----------------
+
+Support for the GHASH and POLYVAL universal hash functions. These algorithms
+are used only as internal components of other algorithms.
+
+.. kernel-doc:: include/crypto/gf128hash.h
+
+MD5
+---
+
+Support for the MD5 cryptographic hash function and HMAC-MD5. This algorithm is
+obsolete and is supported only for backwards compatibility.
+
+.. kernel-doc:: include/crypto/md5.h
+
+NH
+--
+
+Support for the NH universal hash function. This algorithm is used only as an
+internal component of other algorithms.
+
+.. kernel-doc:: include/crypto/nh.h
+
+Poly1305
+--------
+
+Support for the Poly1305 universal hash function. This algorithm is used only
+as an internal component of other algorithms.
+
+.. kernel-doc:: include/crypto/poly1305.h
+
+SHA-1
+-----
+
+Support for the SHA-1 cryptographic hash function and HMAC-SHA1. This algorithm
+is obsolete and is supported only for backwards compatibility.
+
+.. kernel-doc:: include/crypto/sha1.h
+
+SHA-2
+-----
+
+Support for the SHA-2 family of cryptographic hash functions, including SHA-224,
+SHA-256, SHA-384, and SHA-512. This also includes their corresponding HMACs:
+HMAC-SHA224, HMAC-SHA256, HMAC-SHA384, and HMAC-SHA512.
+
+.. kernel-doc:: include/crypto/sha2.h
+
+SHA-3
+-----
+
+The SHA-3 functions are documented in :ref:`sha3`.
+
+SM3
+---
+
+Support for the SM3 cryptographic hash function.
+
+.. kernel-doc:: include/crypto/sm3.h
diff --git a/Documentation/crypto/libcrypto-signature.rst b/Documentation/crypto/libcrypto-signature.rst
new file mode 100644
index 0000000000000..e80d59fa51b6a
--- /dev/null
+++ b/Documentation/crypto/libcrypto-signature.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Digital signature algorithms
+============================
+
+ML-DSA
+------
+
+Support for the ML-DSA digital signature algorithm.
+
+.. kernel-doc:: include/crypto/mldsa.h
diff --git a/Documentation/crypto/libcrypto-utils.rst b/Documentation/crypto/libcrypto-utils.rst
new file mode 100644
index 0000000000000..9d833f47ed390
--- /dev/null
+++ b/Documentation/crypto/libcrypto-utils.rst
@@ -0,0 +1,6 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Utility functions
+=================
+
+.. kernel-doc:: include/crypto/utils.h
diff --git a/Documentation/crypto/libcrypto.rst b/Documentation/crypto/libcrypto.rst
new file mode 100644
index 0000000000000..a1557d45b0e5a
--- /dev/null
+++ b/Documentation/crypto/libcrypto.rst
@@ -0,0 +1,165 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+==============
+Crypto library
+==============
+
+``lib/crypto/`` provides faster and easier access to cryptographic algorithms
+than the traditional crypto API.
+
+Each cryptographic algorithm is supported via a set of dedicated functions.
+"Crypto agility", where needed, is left to calling code.
+
+The crypto library functions are intended to be boring and straightforward, and
+to follow familiar conventions. Their primary documentation is their (fairly
+extensive) kernel-doc. This page just provides some extra high-level context.
+
+Note that the crypto library isn't entirely new. ``lib/`` has contained some
+crypto functions since 2005. Rather, it's just an approach that's been expanded
+over time as it's been found to work well. It also largely just matches how the
+kernel already does things elsewhere.
+
+Scope and intended audience
+===========================
+
+The crypto library documentation is primarily meant for kernel developers who
+need to use a particular cryptographic algorithm(s) in kernel code. For
+example, "I just need to compute a SHA-256 hash." A secondary audience is
+developers working on the crypto algorithm implementations themselves.
+
+If you're looking for more general information about cryptography, like the
+differences between the different crypto algorithms or how to select an
+appropriate algorithm, you should refer to external sources which cover that
+type of information much more comprehensively. If you need help selecting
+algorithms for a new kernel feature that doesn't already have its algorithms
+predefined, please reach out to ``linux-crypto@vger.kernel.org`` for advice.
+
+Code organization
+=================
+
+- ``lib/crypto/*.c``: the crypto algorithm implementations
+
+- ``lib/crypto/$(SRCARCH)/``: architecture-specific code for crypto algorithms.
+ It is here rather than somewhere in ``arch/`` partly because this allows
+ generic and architecture-optimized code to be easily built into a single
+ loadable module (when the algorithm is set to 'm' in the kconfig).
+
+- ``lib/crypto/tests/``: KUnit tests for the crypto algorithms
+
+- ``include/crypto/``: crypto headers, for both the crypto library and the
+ traditional crypto API
+
+Generally, there is one kernel module per algorithm. Sometimes related
+algorithms are grouped into one module. There is intentionally no common
+framework, though there are some utility functions that multiple algorithms use.
+
+Each algorithm module is controlled by a tristate kconfig symbol
+``CRYPTO_LIB_$(ALGORITHM)``. As is the norm for library functions in the
+kernel, these are hidden symbols which don't show up in the kconfig menu.
+Instead, they are just selected by all the kconfig symbols that need them.
+
+Many of the algorithms have multiple implementations: a generic implementation
+and architecture-optimized implementation(s). Each module initialization
+function, or initcall in the built-in case, automatically enables the best
+implementation based on the available CPU features.
+
+Note that the crypto library doesn't use the ``crypto/``,
+``arch/$(SRCARCH)/crypto/``, or ``drivers/crypto/`` directories. These
+directories are used by the traditional crypto API. When possible, algorithms
+in the traditional crypto API are implemented by calls into the library.
+
+Advantages
+==========
+
+Some of the advantages of the library over the traditional crypto API are:
+
+- The library functions tend to be much easier to use. For example, a hash
+ value can be computed using only a single function call. Most of the library
+ functions always succeed and return void, eliminating the need to write
+ error-handling code. Most also accept standard virtual addresses, rather than
+ scatterlists which are difficult and less efficient to work with.
+
+- The library functions are usually faster, especially for short inputs. They
+ call the crypto algorithms directly without inefficient indirect calls, memory
+ allocations, string parsing, lookups in an algorithm registry, and other
+ unnecessary API overhead. Architecture-optimized code is enabled by default.
+
+- The library functions use standard link-time dependencies instead of
+ error-prone dynamic loading by name. There's no need for workarounds such as
+ forcing algorithms to be built-in or adding module soft dependencies.
+
+- The library focuses on the approach that works the best on the vast majority
+ of systems: CPU-based implementations of the crypto algorithms, utilizing
+ on-CPU acceleration (such as AES instructions) when available.
+
+- The library uses standard KUnit tests, rather than custom ad-hoc tests.
+
+- The library tends to have higher assurance implementations of the crypto
+ algorithms. This is both due to its simpler design and because more of its
+ code is being regularly tested.
+
+- The library supports features that don't fit into the rigid framework of the
+ traditional crypto API, for example interleaved hashing and XOFs.
+
+When to use it
+==============
+
+In-kernel users should use the library (rather than the traditional crypto API)
+whenever possible. Many subsystems have already been converted. It usually
+simplifies their code significantly and improves performance.
+
+Some kernel features allow userspace to provide an arbitrary string that selects
+an arbitrary algorithm from the traditional crypto API by name. These features
+generally will have to keep using the traditional crypto API for backwards
+compatibility.
+
+Note: new kernel features shouldn't support every algorithm, but rather make a
+deliberate choice about what algorithm(s) to support. History has shown that
+making a deliberate, thoughtful choice greatly simplifies code maintenance,
+reduces the chance for mistakes (such as using an obsolete, insecure, or
+inappropriate algorithm), and makes your feature easier to use.
+
+Testing
+=======
+
+The crypto library uses standard KUnit tests. Like many of the kernel's other
+KUnit tests, they are included in the set of tests that is run by
+``tools/testing/kunit/kunit.py run --alltests``.
+
+A ``.kunitconfig`` file is also provided to run just the crypto library tests.
+For example, here's how to run them in user-mode Linux:
+
+.. code-block:: sh
+
+ tools/testing/kunit/kunit.py run --kunitconfig=lib/crypto/
+
+Many of the crypto algorithms have architecture-optimized implementations.
+Testing those requires building an appropriate kernel and running the tests
+either in QEMU or on appropriate hardware. Here's one example with QEMU:
+
+.. code-block:: sh
+
+ tools/testing/kunit/kunit.py run --kunitconfig=lib/crypto/ --arch=arm64 --make_options LLVM=1
+
+Depending on the code being tested, flags may need to be passed to QEMU to
+emulate the correct type of hardware for the code to be reached.
+
+Since correctness is essential in cryptographic code, new architecture-optimized
+code is accepted only if it can be tested in QEMU.
+
+Note: the crypto library also includes FIPS 140 self-tests. These are
+lightweight, are designed specifically to meet FIPS 140 requirements, and exist
+*only* to meet those requirements. Normal testing done by kernel developers and
+integrators should use the much more comprehensive KUnit tests instead.
+
+API documentation
+=================
+
+.. toctree::
+ :maxdepth: 2
+
+ libcrypto-blockcipher
+ libcrypto-hash
+ libcrypto-signature
+ libcrypto-utils
+ sha3
diff --git a/Documentation/crypto/sha3.rst b/Documentation/crypto/sha3.rst
index 37640f295118b..250669c98f6ba 100644
--- a/Documentation/crypto/sha3.rst
+++ b/Documentation/crypto/sha3.rst
@@ -1,7 +1,9 @@
.. SPDX-License-Identifier: GPL-2.0-or-later
+.. _sha3:
+
==========================
SHA-3 Algorithm Collection
==========================
.. contents::
--
2.53.0
^ permalink raw reply related [flat|nested] 5+ messages in thread