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    Subject[PATCH net-next v8 03/28] zinc: introduce minimal cryptography library
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    Zinc stands for "Zinc Is Neat Crypto" or "Zinc as IN Crypto". It's also
    short, easy to type, and plays nicely with the recent trend of naming
    crypto libraries after elements. The guiding principle is "don't overdo
    it". It's less of a library and more of a directory tree for organizing
    well-curated direct implementations of cryptography primitives.

    Zinc is a new cryptography API that is much more minimal and lower-level
    than the current one. It intends to complement it and provide a basis
    upon which the current crypto API might build, as the provider of
    software implementations of cryptographic primitives. It is motivated by
    three primary observations in crypto API design:

    * Highly composable "cipher modes" and related abstractions from the
    90s did not turn out to be as terrific an idea as hoped, leading to
    a host of API misuse problems.

    * Most programmers are afraid of crypto code, and so prefer to
    integrate it into libraries in a highly abstracted manner, so as to
    shield themselves from implementation details. Cryptographers, on
    the other hand, prefer simple direct implementations, which they're
    able to verify for high assurance and optimize in accordance with
    their expertise.

    * Overly abstracted and flexible cryptography APIs lead to a host of
    dangerous problems and performance issues. The kernel is in the
    business usually not of coming up with new uses of crypto, but
    rather implementing various constructions, which means it essentially
    needs a library of primitives, not a highly abstracted enterprise-ready
    pluggable system, with a few particular exceptions.

    This last observation has seen itself play out several times over and
    over again within the kernel:

    * The perennial move of actual primitives away from crypto/ and into
    lib/, so that users can actually call these functions directly with
    no overhead and without lots of allocations, function pointers,
    string specifier parsing, and general clunkiness. For example:
    sha256, chacha20, siphash, sha1, and so forth live in lib/ rather
    than in crypto/. Zinc intends to stop the cluttering of lib/ and
    introduce these direct primitives into their proper place, lib/zinc/.

    * An abundance of misuse bugs with the present crypto API that have
    been very unpleasant to clean up.

    * A hesitance to even use cryptography, because of the overhead and
    headaches involved in accessing the routines.

    Zinc goes in a rather different direction. Rather than providing a
    thoroughly designed and abstracted API, Zinc gives you simple functions,
    which implement some primitive, or some particular and specific
    construction of primitives. It is not dynamic in the least, though one
    could imagine implementing a complex dynamic dispatch mechanism (such as
    the current crypto API) on top of these basic functions. After all,
    dynamic dispatch is usually needed for applications with cipher agility,
    such as IPsec, dm-crypt, AF_ALG, and so forth, and the existing crypto
    API will continue to play that role. However, Zinc will provide a non-
    haphazard way of directly utilizing crypto routines in applications
    that do have neither the need nor desire for abstraction and dynamic
    dispatch.

    It also organizes the implementations in a simple, straight-forward,
    and direct manner, making it enjoyable and intuitive to work on.
    Rather than moving optimized assembly implementations into arch/, it
    keeps them all together in lib/zinc/, making it simple and obvious to
    compare and contrast what's happening. This is, notably, exactly what
    the lib/raid6/ tree does, and that seems to work out rather well. It's
    also the pattern of most successful crypto libraries. The architecture-
    specific glue-code is made a part of each translation unit, rather than
    being in a separate one, so that generic and architecture-optimized code
    are combined at compile-time, and incompatibility branches compiled out by
    the optimizer.

    All implementations have been extensively tested and fuzzed, and are
    selected for their quality, trustworthiness, and performance. Wherever
    possible and performant, formally verified implementations are used,
    such as those from HACL* [1] and Fiat-Crypto [2]. The routines also take
    special care to zero out secrets using memzero_explicit (and future work
    is planned to have gcc do this more reliably and performantly with
    compiler plugins). The performance of the selected implementations is
    state-of-the-art and unrivaled on a broad array of hardware, though of
    course we will continue to fine tune these to the hardware demands
    needed by kernel contributors. Each implementation also comes with
    extensive self-tests and crafted test vectors, pulled from various
    places such as Wycheproof [9].

    Regularity of function signatures is important, so that users can easily
    "guess" the name of the function they want. Though, individual
    primitives are oftentimes not trivially interchangeable, having been
    designed for different things and requiring different parameters and
    semantics, and so the function signatures they provide will directly
    reflect the realities of the primitives' usages, rather than hiding it
    behind (inevitably leaky) abstractions. Also, in contrast to the current
    crypto API, Zinc functions can work on stack buffers, and can be called
    with different keys, without requiring allocations or locking.

    SIMD is used automatically when available, though some routines may
    benefit from either having their SIMD disabled for particular
    invocations, or to have the SIMD initialization calls amortized over
    several invocations of the function, and so Zinc utilizes function
    signatures enabling that in conjunction with the recently introduced
    simd_context_t.

    More generally, Zinc provides function signatures that allow just what
    is required by the various callers. This isn't to say that users of the
    functions will be permitted to pollute the function semantics with weird
    particular needs, but we are trying very hard not to overdo it, and that
    means looking carefully at what's actually necessary, and doing just that,
    and not much more than that. Remember: practicality and cleanliness rather
    than over-zealous infrastructure.

    Zinc provides also an opening for the best implementers in academia to
    contribute their time and effort to the kernel, by being sufficiently
    simple and inviting. In discussing this commit with some of the best and
    brightest over the last few years, there are many who are eager to
    devote rare talent and energy to this effort.

    Following the merging of this, I expect for the primitives that
    currently exist in lib/ to work their way into lib/zinc/, after intense
    scrutiny of each implementation, potentially replacing them with either
    formally-verified implementations, or better studied and faster
    state-of-the-art implementations.

    Also following the merging of this, I expect for the old crypto API
    implementations to be ported over to use Zinc for their software-based
    implementations.

    As Zinc is simply library code, its config options are un-menued, with
    the exception of CONFIG_ZINC_SELFTEST and CONFIG_ZINC_DEBUG, which enables
    various selftests and debugging conditions.

    [1] https://github.com/project-everest/hacl-star
    [2] https://github.com/mit-plv/fiat-crypto
    [3] https://cr.yp.to/ecdh.html
    [4] https://cr.yp.to/chacha.html
    [5] https://cr.yp.to/snuffle/xsalsa-20081128.pdf
    [6] https://cr.yp.to/mac.html
    [7] https://blake2.net/
    [8] https://tools.ietf.org/html/rfc8439
    [9] https://github.com/google/wycheproof

    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Cc: Samuel Neves <sneves@dei.uc.pt>
    Cc: Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Greg KH <gregkh@linuxfoundation.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: kernel-hardening@lists.openwall.com
    Cc: linux-crypto@vger.kernel.org
    ---
    MAINTAINERS | 8 ++++++++
    lib/Kconfig | 2 ++
    lib/Makefile | 2 ++
    lib/zinc/Kconfig | 41 +++++++++++++++++++++++++++++++++++++++++
    lib/zinc/Makefile | 3 +++
    5 files changed, 56 insertions(+)
    create mode 100644 lib/zinc/Kconfig
    create mode 100644 lib/zinc/Makefile

    diff --git a/MAINTAINERS b/MAINTAINERS
    index 7f1399ac028e..c0d078d4dbd8 100644
    --- a/MAINTAINERS
    +++ b/MAINTAINERS
    @@ -16230,6 +16230,14 @@ Q: https://patchwork.linuxtv.org/project/linux-media/list/
    S: Maintained
    F: drivers/media/dvb-frontends/zd1301_demod*

    +ZINC CRYPTOGRAPHY LIBRARY
    +M: Jason A. Donenfeld <Jason@zx2c4.com>
    +M: Samuel Neves <sneves@dei.uc.pt>
    +S: Maintained
    +F: lib/zinc/
    +F: include/zinc/
    +L: linux-crypto@vger.kernel.org
    +
    ZPOOL COMPRESSED PAGE STORAGE API
    M: Dan Streetman <ddstreet@ieee.org>
    L: linux-mm@kvack.org
    diff --git a/lib/Kconfig b/lib/Kconfig
    index a3928d4438b5..3e6848269c66 100644
    --- a/lib/Kconfig
    +++ b/lib/Kconfig
    @@ -485,6 +485,8 @@ config GLOB_SELFTEST
    module load) by a small amount, so you're welcome to play with
    it, but you probably don't need it.

    +source "lib/zinc/Kconfig"
    +
    #
    # Netlink attribute parsing support is select'ed if needed
    #
    diff --git a/lib/Makefile b/lib/Makefile
    index 423876446810..7a04d7ce95a6 100644
    --- a/lib/Makefile
    +++ b/lib/Makefile
    @@ -213,6 +213,8 @@ obj-$(CONFIG_PERCPU_TEST) += percpu_test.o

    obj-$(CONFIG_ASN1) += asn1_decoder.o

    +obj-y += zinc/
    +
    obj-$(CONFIG_FONT_SUPPORT) += fonts/

    obj-$(CONFIG_PRIME_NUMBERS) += prime_numbers.o
    diff --git a/lib/zinc/Kconfig b/lib/zinc/Kconfig
    new file mode 100644
    index 000000000000..90e066ea93a0
    --- /dev/null
    +++ b/lib/zinc/Kconfig
    @@ -0,0 +1,41 @@
    +config ZINC_SELFTEST
    + bool "Zinc cryptography library self-tests"
    + help
    + This builds a series of self-tests for the Zinc crypto library, which
    + help diagnose any cryptographic algorithm implementation issues that
    + might be at the root cause of potential bugs. It also adds various
    + traps for incorrect usage.
    +
    + Unless you are optimizing for machines without much disk space or for
    + very slow machines, it is probably a good idea to say Y here, so that
    + any potential cryptographic bugs translate into easy bug reports
    + rather than long-lasting security issues.
    +
    +config ZINC_DEBUG
    + bool "Zinc cryptography library debugging"
    + help
    + This turns on a series of additional checks and debugging options
    + that are useful for developers but probably will not provide much
    + benefit to end users.
    +
    + Most people should say N here.
    +
    +config ZINC_ARCH_ARM
    + def_bool y
    + depends on ARM
    +
    +config ZINC_ARCH_ARM64
    + def_bool y
    + depends on ARM64
    +
    +config ZINC_ARCH_X86_64
    + def_bool y
    + depends on X86_64 && !UML
    +
    +config ZINC_ARCH_MIPS
    + def_bool y
    + depends on MIPS && CPU_MIPS32_R2 && !64BIT
    +
    +config ZINC_ARCH_MIPS64
    + def_bool y
    + depends on MIPS && 64BIT
    diff --git a/lib/zinc/Makefile b/lib/zinc/Makefile
    new file mode 100644
    index 000000000000..a61c80d676cb
    --- /dev/null
    +++ b/lib/zinc/Makefile
    @@ -0,0 +1,3 @@
    +ccflags-y := -O2
    +ccflags-y += -D'pr_fmt(fmt)="zinc: " fmt'
    +ccflags-$(CONFIG_ZINC_DEBUG) += -DDEBUG
    --
    2.19.1
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