Re: [PATCH net-next v5 02/20] zinc: introduce minimal cryptography library

From: Ard Biesheuvel
Date: Tue Sep 25 2018 - 06:25:39 EST

Hi Jason,

I have another couple of questions which are unrelated to the below,
so I will just respond again to the top message.

On Tue, 18 Sep 2018 at 18:18, Jason A. Donenfeld <Jason@xxxxxxxxx> wrote:
> Zinc stands for "Zinc Is Neat Crypto" or "Zinc as IN Crypto" or maybe
> just "Zx2c4's INsane Cryptolib." 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.

Kees is currently dealing with VLA uses in crypto API skcipher
invocations [0] that don't benefit from its async capabilities nor
from the runtime resolution of cipher name strings, given that they
always select the same one.

drivers/net/ppp/ppp_mppe.c: "ecb(arc4)"
drivers/usb/wusbcore/crypto.c: "cbc(aes)"
net/ceph/crypto.c: "cbc(aes)"
net/mac802154/llsec.c: "ctr(aes)"
net/rxrpc/rxkad.c: "pcbc(fcrypt)"
net/rxrpc/rxkad.c: "pcbc(fcrypt)"
net/sunrpc/auth_gss/gss_krb5_mech.c: "cbc(des)"
net/sunrpc/auth_gss/gss_krb5_mech.c: "ecb(arc4)"
net/sunrpc/auth_gss/gss_krb5_mech.c: "cbc(des3_ede)"
net/sunrpc/auth_gss/gss_krb5_mech.c: "cts(cbc(aes))"
net/sunrpc/auth_gss/gss_krb5_mech.c: "cts(cbc(aes))"
net/wireless/lib80211_crypt_tkip.c: "ecb(arc4)"
net/wireless/lib80211_crypt_wep.c: "ecb(arc4)"

To me, these are prime candidates for moving into your library [at
some point]. I guess AES should be non-controversial, but moving the
others is actually more important in my view, since we will be able to
stop exposing them via the crypto API in that case. Any thoughts?

> [From 00/20] ..., WireGuard patches will go through
> DaveM's net-next tree, while Zinc patches will go through Greg KH's tree.

Given the cross dependencies, I'd prefer it if we take these through
Herbert's tree [which feeds into DaveM's tree as well].

Also, you haven't yet responded to my question about WireGuard's
limitation to synchronous encryption, or whether and how you expect to
support asynchronous accelerators for ChaCha20/Poly1305 in the future.
This shouldn't impede adoption of this series, but this is something
that is going to come up sooner than you think, and so I would like to
understand whether this means your library will grow asynchronous
interfaces as well, or whether it will be moved to the crypto API.
(Also, I'd like to know whether the RFC7539 construction of ChaCha20
and Poly1305 is compatible with WireGuard's)



> 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
> 90s cryptographers 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_DEBUG, which enables various selftests and
> BUG_ONs.
> [1]
> [2]
> [3]
> [4]
> [5]
> [6]
> [7]
> [8]
> [9]
> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
> Cc: Samuel Neves <sneves@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Jean-Philippe Aumasson <jeanphilippe.aumasson@xxxxxxxxx>
> ---
> MAINTAINERS | 8 ++++++++
> lib/Kconfig | 2 ++
> lib/Makefile | 2 ++
> lib/zinc/Kconfig | 32 ++++++++++++++++++++++++++++++++
> lib/zinc/Makefile | 4 ++++
> 5 files changed, 48 insertions(+)
> create mode 100644 lib/zinc/Kconfig
> create mode 100644 lib/zinc/Makefile
> index 4327777dce57..5967c737f3ce 100644
> @@ -16170,6 +16170,14 @@ Q:
> S: Maintained
> F: drivers/media/dvb-frontends/zd1301_demod*
> +M: Jason A. Donenfeld <Jason@xxxxxxxxx>
> +M: Samuel Neves <sneves@xxxxxxxxx>
> +S: Maintained
> +F: lib/zinc/
> +F: include/zinc/
> +L: linux-crypto@xxxxxxxxxxxxxxx
> +
> M: Dan Streetman <ddstreet@xxxxxxxx>
> L: linux-mm@xxxxxxxxx
> 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 ca3f7ebb900d..571d28d3f143 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -214,6 +214,8 @@ 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..4e2e59126a67
> --- /dev/null
> +++ b/lib/zinc/Kconfig
> @@ -0,0 +1,32 @@
> +config ZINC_DEBUG
> + bool "Zinc cryptography library debugging and 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
> + debugging traps.
> +
> + Unless you're developing and testing cryptographic routines, or are
> + especially paranoid about correctness on your hardware, you may say
> + N here.
> +
> +config ZINC_ARCH_ARM
> + def_bool y
> + depends on ARM && !64BIT
> +
> +config ZINC_ARCH_ARM64
> + def_bool y
> + depends on ARM64 && 64BIT
> +
> +config ZINC_ARCH_X86_64
> + def_bool y
> + depends on X86_64 && 64BIT
> + depends on !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..83dfd63988c0
> --- /dev/null
> +++ b/lib/zinc/Makefile
> @@ -0,0 +1,4 @@
> +ccflags-y := -O3
> +ccflags-y += -Wframe-larger-than=$(if (CONFIG_KASAN),16384,8192)
> +ccflags-y += -D'pr_fmt(fmt)="zinc: " fmt'
> +ccflags-$(CONFIG_ZINC_DEBUG) += -DDEBUG
> --
> 2.19.0