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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-24 08:46:03 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-24 08:46:03 -0700 |
| commit | cf9610f9116d55c5a66ef9f1faecacabd93a9322 (patch) | |
| tree | 757a3d280760c654767631cab5ad8af2d86d1848 /Documentation/crypto/libcrypto.rst | |
| download | linux-stable-cf9610f9116d55c5a66ef9f1faecacabd93a9322.tar.gz linux-stable-cf9610f9116d55c5a66ef9f1faecacabd93a9322.zip | |
Merge tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrlgrafted
Pull pin control updates from Linus Walleij:
"Core changes:
- Use the non-blocking mux_state_try_select() in the generic MUX pin
control back-end
- Free pin maps on pinctrl_generic_to_map() failure in the core
helpers
New hardware pin control:
- Qualcomm Maili TLMM SoC, PMG1110 PMIC, and Eliza LPASS LPI TLMM SoC
(this is for the low power audio, LPASS = Low Power Audio SubSystem
portions)
- Upboard support on top of the Intel pin controller
- Apple T6030 and T6031 support (just compatible strings)
- Samsung Exynos 8855 SoC
- Mediatek MT6858 SoC
- Rockchip RK3308B and RV1106 SoCs
- Airoha EN7523 and AN7563 SoCs
Improvements:
- Qualcomm TLMM GPIOs are unconditionally marked as wakeup capable
- Qualcomm improvements on top of the Qualcomm PDC (power domain
controller) irqchip improvements from tglx:s tree
- Qualcomm IPQ806x and IPQ9650 non-urgent pin grop fixups
- The NPCM8xx driver has been put into shape fixing many pin and
group definitions
- Some non-urgent Tegra 264 pin assignments are fixed up
- Some non-urgent fixups to Airoha AN7581 and AN7583 registers and
pin assignments, missing features etc"
* tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl: (130 commits)
dt-bindings: pinctrl: Convert TI DA850 pupd to DT schema
pinctrl: meson: sync some modify from A4
pinctrl: meson: a4: Add input enable pin configuration
pinctrl: realtek: rtd1625: remove unused group name spdif_sel
pinctrl: realtek: rtd1625: fix base_bit for VE4 GPIO 13
dt-bindings: pinctrl: microchip,pic32mzda-pinctrl: Convert to DT schema
Revert "Merge branch 'ib-rsk7204' into devel"
pinctrl: rockchip: Add RV1106 pinctrl support
dt-bindings: pinctrl: rockchip: Add RV1106 compatible
pinctrl: rockchip: Decode drive strength in the get function
pinctrl: fix PINCTRL_GENERIC_MUX not always being selectable
pinctrl: airoha: add support of an7563 SoC
dt-bindings: pinctrl: airoha: add support of an7563 pin controller
pinctrl: airoha: try to find chip scu node by phandle first
pinctrl: airoha: add support of en7523 SoC
dt-bindings: pinctrl: airoha: add support of en7523 pin controller
pinctrl: airoha: an7583: add support for olt pinmux
pinctrl: airoha: an7583: add support for pon_alt pinmux
pinctrl: airoha: an7583: add support for npu_uart pinmux
dt-bindings: pinctrl: airoha: an7583: add missed features
...
Diffstat (limited to 'Documentation/crypto/libcrypto.rst')
| -rw-r--r-- | Documentation/crypto/libcrypto.rst | 168 |
1 files changed, 168 insertions, 0 deletions
diff --git a/Documentation/crypto/libcrypto.rst b/Documentation/crypto/libcrypto.rst new file mode 100644 index 000000000..e911e0521 --- /dev/null +++ b/Documentation/crypto/libcrypto.rst @@ -0,0 +1,168 @@ +.. SPDX-License-Identifier: GPL-2.0-or-later + +============== +Crypto library +============== + +The Linux kernel's crypto library (``lib/crypto/``) provides kernel-internal +users of cryptographic algorithms with faster and easier access to those +algorithms than the traditional kernel 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-auth-encryption + libcrypto-blockcipher + libcrypto-hash + libcrypto-signature + libcrypto-unauth-encryption + libcrypto-utils + sha3 |
