Use hardware acceleration for SHA256 (#2426)

## Proposed Changes

Modify the SHA256 implementation in `eth2_hashing` so that it switches between `ring` and `sha2` to take advantage of [x86_64 SHA extensions](https://en.wikipedia.org/wiki/Intel_SHA_extensions). The extensions are available on modern Intel and AMD CPUs, and seem to provide a considerable speed-up: on my Ryzen 5950X it dropped state tree hashing times by about 30% from 35ms to 25ms (on Prater).

## Additional Info

The extensions became available in the `sha2` crate [last year](https://www.reddit.com/r/rust/comments/hf2vcx/ann_rustcryptos_sha1_and_sha2_now_support/), and are not available in Ring, which uses a [pure Rust implementation of sha2](https://github.com/briansmith/ring/blob/main/src/digest/sha2.rs). Ring is faster on CPUs that lack the extensions so I've implemented a runtime switch to use `sha2` only when the extensions are available. The runtime switching seems to impose a miniscule penalty (see the benchmarks linked below).

Cargo.lock

@@ -1941,6 +1941,7 @@ dependencies = [
 name = "eth2_hashing"
 version = "0.1.1"
 dependencies = [
+ "cpufeatures",
  "lazy_static",
  "ring",
  "rustc-hex",
@@ -3736,6 +3737,7 @@ dependencies = [
  "directory",
  "env_logger 0.8.4",
  "environment",
+ "eth2_hashing",
  "eth2_libp2p",
  "eth2_network_config",
  "futures",

consensus/swap_or_not_shuffle/src/compute_shuffled_index.rs

@@ -1,5 +1,5 @@
 use crate::Hash256;
-use eth2_hashing::{Context, SHA256};
+use eth2_hashing::{Context, Sha256Context};
 use std::cmp::max;
 
 /// Return `p(index)` in a pseudorandom permutation `p` of `0...list_size-1` with ``seed`` as entropy.
@@ -54,7 +54,7 @@ fn do_round(seed: &[u8], index: usize, pivot: usize, round: u8, list_size: usize
 }
 
 fn hash_with_round_and_position(seed: &[u8], round: u8, position: usize) -> Hash256 {
-    let mut context = Context::new(&SHA256);
+    let mut context = Context::new();
 
     context.update(seed);
     context.update(&[round]);
@@ -64,17 +64,17 @@ fn hash_with_round_and_position(seed: &[u8], round: u8, position: usize) -> Hash
      */
     context.update(&(position / 256).to_le_bytes()[0..4]);
 
-    let digest = context.finish();
+    let digest = context.finalize();
     Hash256::from_slice(digest.as_ref())
 }
 
 fn hash_with_round(seed: &[u8], round: u8) -> Hash256 {
-    let mut context = Context::new(&SHA256);
+    let mut context = Context::new();
 
     context.update(seed);
     context.update(&[round]);
 
-    let digest = context.finish();
+    let digest = context.finalize();
     Hash256::from_slice(digest.as_ref())
 }
 

consensus/swap_or_not_shuffle/src/shuffle_list.rs

@@ -1,5 +1,5 @@
 use crate::Hash256;
-use eth2_hashing::{Context, SHA256};
+use eth2_hashing::hash_fixed;
 use std::mem;
 
 const SEED_SIZE: usize = 32;
@@ -31,12 +31,10 @@ impl Buf {
     /// Returns the new pivot. It is "raw" because it has not modulo the list size (this must be
     /// done by the caller).
     fn raw_pivot(&self) -> u64 {
-        let mut context = Context::new(&SHA256);
+        let digest = hash_fixed(&self.0[0..PIVOT_VIEW_SIZE]);
-        context.update(&self.0[0..PIVOT_VIEW_SIZE]);
-        let digest = context.finish();
 
         let mut bytes = [0; mem::size_of::<u64>()];
-        bytes[..].copy_from_slice(&digest.as_ref()[0..mem::size_of::<u64>()]);
+        bytes[..].copy_from_slice(&digest[0..mem::size_of::<u64>()]);
         u64::from_le_bytes(bytes)
     }
 
@@ -47,10 +45,7 @@ impl Buf {
 
     /// Hash the entire buffer.
     fn hash(&self) -> Hash256 {
-        let mut context = Context::new(&SHA256);
+        Hash256::from_slice(&hash_fixed(&self.0))
-        context.update(&self.0[..]);
-        let digest = context.finish();
-        Hash256::from_slice(digest.as_ref())
     }
 }
 

consensus/tree_hash/src/lib.rs

@@ -7,8 +7,7 @@ pub use merkle_hasher::{Error, MerkleHasher};
 pub use merkleize_padded::merkleize_padded;
 pub use merkleize_standard::merkleize_standard;
 
-use eth2_hashing::{Context, SHA256};
+use eth2_hashing::{hash_fixed, ZERO_HASHES, ZERO_HASHES_MAX_INDEX};
-use eth2_hashing::{ZERO_HASHES, ZERO_HASHES_MAX_INDEX};
 
 pub const BYTES_PER_CHUNK: usize = 32;
 pub const HASHSIZE: usize = 32;
@@ -39,11 +38,7 @@ pub fn merkle_root(bytes: &[u8], minimum_leaf_count: usize) -> Hash256 {
         let mut leaves = [0; HASHSIZE * 2];
         leaves[0..bytes.len()].copy_from_slice(bytes);
 
-        let mut context = Context::new(&SHA256);
+        Hash256::from_slice(&hash_fixed(&leaves))
-        context.update(&leaves);
-        let digest = context.finish();
-
-        Hash256::from_slice(digest.as_ref())
     } else {
         // If there are 3 or more leaves, use `MerkleHasher`.
         let mut hasher = MerkleHasher::with_leaves(leaves);

consensus/tree_hash/src/merkle_hasher.rs

@@ -1,5 +1,5 @@
 use crate::{get_zero_hash, Hash256, HASHSIZE};
-use eth2_hashing::{Context, Digest, SHA256};
+use eth2_hashing::{Context, Sha256Context, HASH_LEN};
 use smallvec::{smallvec, SmallVec};
 use std::mem;
 
@@ -15,7 +15,7 @@ pub enum Error {
 ///
 /// Should be used as a left or right value for some node.
 enum Preimage<'a> {
-    Digest(Digest),
+    Digest([u8; HASH_LEN]),
     Slice(&'a [u8]),
 }
 
@@ -41,7 +41,7 @@ struct HalfNode {
 impl HalfNode {
     /// Create a new half-node from the given `left` value.
     fn new(id: usize, left: Preimage) -> Self {
-        let mut context = Context::new(&SHA256);
+        let mut context = Context::new();
         context.update(left.as_bytes());
 
         Self { context, id }
@@ -49,9 +49,9 @@ impl HalfNode {
 
     /// Complete the half-node by providing a `right` value. Returns a digest of the left and right
     /// nodes.
-    fn finish(mut self, right: Preimage) -> Digest {
+    fn finish(mut self, right: Preimage) -> [u8; HASH_LEN] {
         self.context.update(right.as_bytes());
-        self.context.finish()
+        self.context.finalize()
     }
 }
 
@@ -124,7 +124,7 @@ pub struct MerkleHasher {
     /// Stores the nodes that are half-complete and awaiting a right node.
     ///
     /// A smallvec of size 8 means we can hash a tree with 256 leaves without allocating on the
-    /// heap. Each half-node is 224 bytes, so this smallvec may store 1,792 bytes on the stack.
+    /// heap. Each half-node is 232 bytes, so this smallvec may store 1856 bytes on the stack.
     half_nodes: SmallVec8<HalfNode>,
     /// The depth of the tree that will be produced.
     ///
@@ -368,7 +368,7 @@ mod test {
     fn context_size() {
         assert_eq!(
             mem::size_of::<HalfNode>(),
-            216 + 8,
+            232,
             "Halfnode size should be as expected"
         );
     }

consensus/tree_hash/src/merkleize_padded.rs

@@ -1,5 +1,5 @@
 use super::{get_zero_hash, Hash256, BYTES_PER_CHUNK};
-use eth2_hashing::{hash, hash32_concat};
+use eth2_hashing::{hash32_concat, hash_fixed};
 
 /// Merkleize `bytes` and return the root, optionally padding the tree out to `min_leaves` number of
 /// leaves.
@@ -79,7 +79,7 @@ pub fn merkleize_padded(bytes: &[u8], min_leaves: usize) -> Hash256 {
         // Hash two chunks, creating a parent chunk.
         let hash = match bytes.get(start..start + BYTES_PER_CHUNK * 2) {
             // All bytes are available, hash as usual.
-            Some(slice) => hash(slice),
+            Some(slice) => hash_fixed(slice),
             // Unable to get all the bytes, get a small slice and pad it out.
             None => {
                 let mut preimage = bytes
@@ -87,7 +87,7 @@ pub fn merkleize_padded(bytes: &[u8], min_leaves: usize) -> Hash256 {
                     .expect("`i` can only be larger than zero if there are bytes to read")
                     .to_vec();
                 preimage.resize(BYTES_PER_CHUNK * 2, 0);
-                hash(&preimage)
+                hash_fixed(&preimage)
             }
         };
 

crypto/eth2_hashing/Cargo.toml

@@ -8,12 +8,9 @@ description = "Hashing primitives used in Ethereum 2.0"
 
 [dependencies]
 lazy_static = { version = "1.4.0", optional = true }
-
-[target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 ring = "0.16.19"
-
+sha2 = "0.9.5"
-[target.'cfg(target_arch = "wasm32")'.dependencies]
+cpufeatures = "0.1.5"
-sha2 = "0.9.1"
 
 [dev-dependencies]
 rustc-hex = "2.1.0"

crypto/eth2_hashing/src/lib.rs

@@ -1,61 +1,205 @@
-//! Provides a simple hash function utilizing `ring::digest::SHA256`.
+//! Optimized SHA256 for use in Ethereum 2.0.
 //!
-//! The purpose of this crate is to provide an abstraction to whatever hash function Ethereum
+//! The initial purpose of this crate was to provide an abstraction over the hash function used in
-//! 2.0 is using. The hash function has been subject to change during the specification process, so
+//! Ethereum 2.0. The hash function changed during the specification process, so defining it once in
-//! defining it once in this crate makes it easy to replace.
+//! this crate made it easy to replace.
+//!
+//! Now this crate serves primarily as a wrapper over two SHA256 crates: `sha2` and `ring` –
+//! which it switches between at runtime based on the availability of SHA intrinsics.
 
-#[cfg(not(target_arch = "wasm32"))]
+pub use self::DynamicContext as Context;
-pub use ring::digest::{digest, Context, Digest, SHA256};
+use sha2::Digest;
-
-#[cfg(target_arch = "wasm32")]
-use sha2::{Digest, Sha256};
 
 #[cfg(feature = "zero_hash_cache")]
 use lazy_static::lazy_static;
 
-/// Returns the digest of `input`.
+/// Length of a SHA256 hash in bytes.
-///
+pub const HASH_LEN: usize = 32;
-/// Uses `ring::digest::SHA256`.
+
+/// Returns the digest of `input` using the best available implementation.
 pub fn hash(input: &[u8]) -> Vec<u8> {
-    #[cfg(not(target_arch = "wasm32"))]
+    DynamicImpl::best().hash(input)
-    let h = digest(&SHA256, input).as_ref().into();
+}
 
-    #[cfg(target_arch = "wasm32")]
+/// Hash function returning a fixed-size array (to save on allocations).
-    let h = Sha256::digest(input).as_ref().into();
+///
-
+/// Uses the best available implementation based on CPU features.
-    h
+pub fn hash_fixed(input: &[u8]) -> [u8; HASH_LEN] {
+    DynamicImpl::best().hash_fixed(input)
 }
 
 /// Compute the hash of two slices concatenated.
-///
-/// # Panics
-///
-/// Will panic if either `h1` or `h2` are not 32 bytes in length.
-#[cfg(not(target_arch = "wasm32"))]
 pub fn hash32_concat(h1: &[u8], h2: &[u8]) -> [u8; 32] {
-    let mut context = Context::new(&SHA256);
+    let mut ctxt = DynamicContext::new();
-    context.update(h1);
+    ctxt.update(h1);
-    context.update(h2);
+    ctxt.update(h2);
-
+    ctxt.finalize()
-    let mut output = [0; 32];
-    output[..].copy_from_slice(context.finish().as_ref());
-    output
 }
 
-/// Compute the hash of two slices concatenated.
+/// Context trait for abstracting over implementation contexts.
-///
+pub trait Sha256Context {
-/// # Panics
+    fn new() -> Self;
-///
-/// Will panic if either `h1` or `h2` are not 32 bytes in length.
-#[cfg(target_arch = "wasm32")]
-pub fn hash32_concat(h1: &[u8], h2: &[u8]) -> [u8; 32] {
-    let mut preimage = [0; 64];
-    preimage[0..32].copy_from_slice(h1);
-    preimage[32..64].copy_from_slice(h2);
 
-    let mut output = [0; 32];
+    fn update(&mut self, bytes: &[u8]);
-    output[..].copy_from_slice(&hash(&preimage));
+
-    output
+    fn finalize(self) -> [u8; HASH_LEN];
+}
+
+/// Top-level trait implemented by both `sha2` and `ring` implementations.
+pub trait Sha256 {
+    type Context: Sha256Context;
+
+    fn hash(&self, input: &[u8]) -> Vec<u8>;
+
+    fn hash_fixed(&self, input: &[u8]) -> [u8; HASH_LEN];
+}
+
+/// Implementation of SHA256 using the `sha2` crate (fastest on CPUs with SHA extensions).
+struct Sha2CrateImpl;
+
+impl Sha256Context for sha2::Sha256 {
+    fn new() -> Self {
+        sha2::Digest::new()
+    }
+
+    fn update(&mut self, bytes: &[u8]) {
+        sha2::Digest::update(self, bytes)
+    }
+
+    fn finalize(self) -> [u8; HASH_LEN] {
+        sha2::Digest::finalize(self).into()
+    }
+}
+
+impl Sha256 for Sha2CrateImpl {
+    type Context = sha2::Sha256;
+
+    fn hash(&self, input: &[u8]) -> Vec<u8> {
+        Self::Context::digest(input).into_iter().collect()
+    }
+
+    fn hash_fixed(&self, input: &[u8]) -> [u8; HASH_LEN] {
+        Self::Context::digest(input).into()
+    }
+}
+
+/// Implementation of SHA256 using the `ring` crate (fastest on CPUs without SHA extensions).
+pub struct RingImpl;
+
+impl Sha256Context for ring::digest::Context {
+    fn new() -> Self {
+        Self::new(&ring::digest::SHA256)
+    }
+
+    fn update(&mut self, bytes: &[u8]) {
+        self.update(bytes)
+    }
+
+    fn finalize(self) -> [u8; HASH_LEN] {
+        let mut output = [0; HASH_LEN];
+        output.copy_from_slice(self.finish().as_ref());
+        output
+    }
+}
+
+impl Sha256 for RingImpl {
+    type Context = ring::digest::Context;
+
+    fn hash(&self, input: &[u8]) -> Vec<u8> {
+        ring::digest::digest(&ring::digest::SHA256, input)
+            .as_ref()
+            .into()
+    }
+
+    fn hash_fixed(&self, input: &[u8]) -> [u8; HASH_LEN] {
+        let mut ctxt = Self::Context::new(&ring::digest::SHA256);
+        ctxt.update(input);
+        ctxt.finalize()
+    }
+}
+
+/// Default dynamic implementation that switches between available implementations.
+pub enum DynamicImpl {
+    Sha2,
+    Ring,
+}
+
+// Runtime latch for detecting the availability of SHA extensions on x86_64.
+//
+// Inspired by the runtime switch within the `sha2` crate itself.
+#[cfg(target_arch = "x86_64")]
+cpufeatures::new!(x86_sha_extensions, "sha", "sse2", "ssse3", "sse4.1");
+
+#[inline(always)]
+pub fn have_sha_extensions() -> bool {
+    #[cfg(target_arch = "x86_64")]
+    return x86_sha_extensions::get();
+
+    #[cfg(not(target_arch = "x86_64"))]
+    return false;
+}
+
+impl DynamicImpl {
+    /// Choose the best available implementation based on the currently executing CPU.
+    #[inline(always)]
+    pub fn best() -> Self {
+        if have_sha_extensions() {
+            Self::Sha2
+        } else {
+            Self::Ring
+        }
+    }
+}
+
+impl Sha256 for DynamicImpl {
+    type Context = DynamicContext;
+
+    #[inline(always)]
+    fn hash(&self, input: &[u8]) -> Vec<u8> {
+        match self {
+            Self::Sha2 => Sha2CrateImpl.hash(input),
+            Self::Ring => RingImpl.hash(input),
+        }
+    }
+
+    #[inline(always)]
+    fn hash_fixed(&self, input: &[u8]) -> [u8; HASH_LEN] {
+        match self {
+            Self::Sha2 => Sha2CrateImpl.hash_fixed(input),
+            Self::Ring => RingImpl.hash_fixed(input),
+        }
+    }
+}
+
+/// Context encapsulating all implemenation contexts.
+///
+/// This enum ends up being 8 bytes larger than the largest inner context.
+pub enum DynamicContext {
+    Sha2(sha2::Sha256),
+    Ring(ring::digest::Context),
+}
+
+impl Sha256Context for DynamicContext {
+    fn new() -> Self {
+        match DynamicImpl::best() {
+            DynamicImpl::Sha2 => Self::Sha2(Sha256Context::new()),
+            DynamicImpl::Ring => Self::Ring(Sha256Context::new()),
+        }
+    }
+
+    fn update(&mut self, bytes: &[u8]) {
+        match self {
+            Self::Sha2(ctxt) => Sha256Context::update(ctxt, bytes),
+            Self::Ring(ctxt) => Sha256Context::update(ctxt, bytes),
+        }
+    }
+
+    fn finalize(self) -> [u8; HASH_LEN] {
+        match self {
+            Self::Sha2(ctxt) => Sha256Context::finalize(ctxt),
+            Self::Ring(ctxt) => Sha256Context::finalize(ctxt),
+        }
+    }
 }
 
 /// The max index that can be used with `ZERO_HASHES`.

lighthouse/Cargo.toml

@@ -16,8 +16,6 @@ modern = ["bls/supranational-force-adx"]
 milagro = ["bls/milagro"]
 # Support minimal spec (used for testing only).
 spec-minimal = []
-# Support spec v0.12 (used by Medalla testnet).
-spec-v12 = []
 
 [dependencies]
 beacon_node = { "path" = "../beacon_node" }
@@ -26,6 +24,7 @@ slog = { version = "2.5.2", features = ["max_level_trace"] }
 sloggers = "1.0.1"
 types = { "path" = "../consensus/types" }
 bls = { path = "../crypto/bls" }
+eth2_hashing = "0.1.0"
 clap = "2.33.3"
 env_logger = "0.8.2"
 logging = { path = "../common/logging" }

lighthouse/src/main.rs

@@ -7,6 +7,7 @@ use clap::{App, Arg, ArgMatches};
 use clap_utils::flags::DISABLE_MALLOC_TUNING_FLAG;
 use env_logger::{Builder, Env};
 use environment::EnvironmentBuilder;
+use eth2_hashing::have_sha_extensions;
 use eth2_network_config::{Eth2NetworkConfig, DEFAULT_HARDCODED_NETWORK};
 use lighthouse_version::VERSION;
 use malloc_utils::configure_memory_allocator;
@@ -43,10 +44,13 @@ fn main() {
         .long_version(
             format!(
                 "{}\n\
-                 BLS Library: {}\n\
+                 BLS library: {}\n\
-                 Specs: mainnet (true), minimal ({}), v0.12.3 ({})",
+                 SHA256 hardware acceleration: {}\n\
-                 VERSION.replace("Lighthouse/", ""), bls_library_name(),
+                 Specs: mainnet (true), minimal ({})",
-                 cfg!(feature = "spec-minimal"), cfg!(feature = "spec-v12"),
+                 VERSION.replace("Lighthouse/", ""),
+                 bls_library_name(),
+                 have_sha_extensions(),
+                 cfg!(feature = "spec-minimal"),
             ).as_str()
         )
         .arg(
@@ -205,7 +209,7 @@ fn main() {
             EthSpecId::Mainnet => run(EnvironmentBuilder::mainnet(), &matches, testnet_config),
             #[cfg(feature = "spec-minimal")]
             EthSpecId::Minimal => run(EnvironmentBuilder::minimal(), &matches, testnet_config),
-            #[cfg(any(not(feature = "spec-minimal")))]
+            #[cfg(not(feature = "spec-minimal"))]
             other => {
                 eprintln!(
                     "Eth spec `{}` is not supported by this build of Lighthouse",