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Add from_slice_unchecked to tx types (#27)
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Very often the VM needs to convert between arbitrary memory slices into
the tx types. The memory bounds of the VM memory are logically verified
and this is a safe operation.

This pattern of expecting the converted type from a slice via `TryFrom`
is recurrent and should be upgraded into a native function of the type
itself.
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@vlopes11
vlopes11 authored Aug 18, 2021
1 parent bd4f21d commit 72796d5
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Showing 7 changed files with 174 additions and 61 deletions.
51 changes: 33 additions & 18 deletions fuel-tx/src/bytes.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -113,12 +113,14 @@ pub fn store_raw_bytes<'a>(
}

pub fn restore_bytes(mut buf: &[u8]) -> io::Result<(usize, Vec<u8>, &[u8])> {
// Safety: chunks_exact will guarantee the size of the slice is correct
let len = buf
.chunks_exact(WORD_SIZE)
.next()
.map(|chunk| <[u8; WORD_SIZE]>::try_from(chunk).unwrap_or_else(|_| unreachable!()))
.map(|b| unsafe { from_slice_unchecked(b) })
.map(|len| Word::from_be_bytes(len) as usize)
.ok_or_else(eof)?;

buf = &buf[WORD_SIZE..];

let pad = len % WORD_SIZE;
Expand Down Expand Up @@ -167,46 +169,46 @@ where
&mut buf[WORD_SIZE..]
}

pub fn restore_number_unchecked<T>(buf: &[u8]) -> (T, &[u8])
pub unsafe fn restore_number_unchecked<T>(buf: &[u8]) -> (T, &[u8])
where
T: From<Word>,
{
let number = <[u8; WORD_SIZE]>::try_from(&buf[..WORD_SIZE]).unwrap_or_else(|_| unreachable!());
let number = from_slice_unchecked(buf);
let number = Word::from_be_bytes(number).into();

(number, &buf[WORD_SIZE..])
}

pub fn restore_word_unchecked(buf: &[u8]) -> (Word, &[u8]) {
let number = <[u8; WORD_SIZE]>::try_from(&buf[..WORD_SIZE]).unwrap_or_else(|_| unreachable!());
pub unsafe fn restore_word_unchecked(buf: &[u8]) -> (Word, &[u8]) {
let number = from_slice_unchecked(buf);
let number = Word::from_be_bytes(number);

(number, &buf[WORD_SIZE..])
}

pub fn restore_u8_unchecked(buf: &[u8]) -> (u8, &[u8]) {
let number = <[u8; WORD_SIZE]>::try_from(&buf[..WORD_SIZE]).unwrap_or_else(|_| unreachable!());
pub unsafe fn restore_u8_unchecked(buf: &[u8]) -> (u8, &[u8]) {
let number = from_slice_unchecked(buf);
let number = Word::from_be_bytes(number) as u8;

(number, &buf[WORD_SIZE..])
}

pub fn restore_u16_unchecked(buf: &[u8]) -> (u16, &[u8]) {
let number = <[u8; WORD_SIZE]>::try_from(&buf[..WORD_SIZE]).unwrap_or_else(|_| unreachable!());
pub unsafe fn restore_u16_unchecked(buf: &[u8]) -> (u16, &[u8]) {
let number = from_slice_unchecked(buf);
let number = Word::from_be_bytes(number) as u16;

(number, &buf[WORD_SIZE..])
}

pub fn restore_u32_unchecked(buf: &[u8]) -> (u32, &[u8]) {
let number = <[u8; WORD_SIZE]>::try_from(&buf[..WORD_SIZE]).unwrap_or_else(|_| unreachable!());
pub unsafe fn restore_u32_unchecked(buf: &[u8]) -> (u32, &[u8]) {
let number = from_slice_unchecked(buf);
let number = Word::from_be_bytes(number) as u32;

(number, &buf[WORD_SIZE..])
}

pub fn restore_usize_unchecked(buf: &[u8]) -> (usize, &[u8]) {
let number = <[u8; WORD_SIZE]>::try_from(&buf[..WORD_SIZE]).unwrap_or_else(|_| unreachable!());
pub unsafe fn restore_usize_unchecked(buf: &[u8]) -> (usize, &[u8]) {
let number = from_slice_unchecked(buf);
let number = Word::from_be_bytes(number) as usize;

(number, &buf[WORD_SIZE..])
Expand All @@ -216,10 +218,11 @@ pub fn restore_number<T>(buf: &[u8]) -> io::Result<(T, &[u8])>
where
T: From<Word>,
{
// Safe checked memory bounds
let number = buf
.chunks_exact(WORD_SIZE)
.next()
.map(|chunk| <[u8; WORD_SIZE]>::try_from(chunk).unwrap_or_else(|_| unreachable!()))
.map(|b| unsafe { from_slice_unchecked(b) })
.map(|chunk| Word::from_be_bytes(chunk).into())
.ok_or_else(eof)?;

Expand Down Expand Up @@ -247,14 +250,26 @@ pub fn store_array_unchecked<'a, const N: usize>(
&mut buf[N..]
}

pub fn restore_array_unchecked<const N: usize>(buf: &[u8]) -> ([u8; N], &[u8]) {
<[u8; N]>::try_from(&buf[..N])
.map(|array| (array, &buf[N..]))
.unwrap_or_else(|_| unreachable!())
pub unsafe fn restore_array_unchecked<const N: usize>(buf: &[u8]) -> ([u8; N], &[u8]) {
(from_slice_unchecked(buf), &buf[N..])
}

pub fn restore_array<const N: usize>(buf: &[u8]) -> io::Result<([u8; N], &[u8])> {
<[u8; N]>::try_from(&buf[..N])
.map_err(|_| eof())
.map(|array| (array, &buf[N..]))
}

/// Add a conversion from arbitrary slices into arrays
///
/// # Warning
///
/// This function will not panic if the length of the slice is smaller than `N`. Instead, it will
/// cause undefined behavior and read random disowned bytes.
pub unsafe fn from_slice_unchecked<const N: usize>(buf: &[u8]) -> [u8; N] {
let ptr = buf.as_ptr() as *const [u8; N];

// Static assertions are not applicable to runtime length check (e.g. slices).
// This is safe if the size of `bytes` is consistent to `N`
*ptr
}
4 changes: 2 additions & 2 deletions fuel-tx/src/lib.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,6 @@ pub mod consts;
pub mod crypto;

pub use transaction::{
Address, Bytes32, Color, ContractId, Input, Metadata, Output, Salt, Transaction,
ValidationError, Witness,
Address, Bytes32, Bytes4, Bytes8, Color, ContractId, Input, Metadata, Output, Salt,
Transaction, ValidationError, Witness,
};
4 changes: 3 additions & 1 deletion fuel-tx/src/transaction.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,9 @@ mod types;
mod validation;

pub use metadata::Metadata;
pub use types::{Address, Bytes32, Color, ContractId, Input, Output, Salt, Witness};
pub use types::{
Address, Bytes32, Bytes4, Bytes8, Color, ContractId, Input, Output, Salt, Witness,
};
pub use validation::ValidationError;

const WORD_SIZE: usize = mem::size_of::<Word>();
Expand Down
41 changes: 22 additions & 19 deletions fuel-tx/src/transaction/txio.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -146,7 +146,8 @@ impl io::Write for Transaction {
return Err(bytes::eof());
}

let (identifier, buf): (Word, _) = bytes::restore_number_unchecked(buf);
// Safety: buffer size is checked
let (identifier, buf): (Word, _) = unsafe { bytes::restore_number_unchecked(buf) };
let identifier = TransactionRepr::try_from(identifier)?;

match identifier {
Expand All @@ -156,14 +157,15 @@ impl io::Write for Transaction {
return Err(bytes::eof());
}

let (gas_price, buf) = bytes::restore_number_unchecked(buf);
let (gas_limit, buf) = bytes::restore_number_unchecked(buf);
let (maturity, buf) = bytes::restore_number_unchecked(buf);
let (script_len, buf) = bytes::restore_usize_unchecked(buf);
let (script_data_len, buf) = bytes::restore_usize_unchecked(buf);
let (inputs_len, buf) = bytes::restore_usize_unchecked(buf);
let (outputs_len, buf) = bytes::restore_usize_unchecked(buf);
let (witnesses_len, buf) = bytes::restore_usize_unchecked(buf);
// Safety: buffer size is checked
let (gas_price, buf) = unsafe { bytes::restore_number_unchecked(buf) };
let (gas_limit, buf) = unsafe { bytes::restore_number_unchecked(buf) };
let (maturity, buf) = unsafe { bytes::restore_number_unchecked(buf) };
let (script_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (script_data_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (inputs_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (outputs_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (witnesses_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };

let (size, script, buf) = bytes::restore_raw_bytes(buf, script_len)?;
n += size;
Expand Down Expand Up @@ -213,16 +215,17 @@ impl io::Write for Transaction {
return Err(bytes::eof());
}

let (gas_price, buf) = bytes::restore_number_unchecked(buf);
let (gas_limit, buf) = bytes::restore_number_unchecked(buf);
let (maturity, buf) = bytes::restore_number_unchecked(buf);
let (_bytecode_length, buf) = bytes::restore_u16_unchecked(buf);
let (bytecode_witness_index, buf) = bytes::restore_u8_unchecked(buf);
let (static_contracts_len, buf) = bytes::restore_usize_unchecked(buf);
let (inputs_len, buf) = bytes::restore_usize_unchecked(buf);
let (outputs_len, buf) = bytes::restore_usize_unchecked(buf);
let (witnesses_len, buf) = bytes::restore_usize_unchecked(buf);
let (salt, mut buf) = bytes::restore_array_unchecked(buf);
// Safety: buffer size is checked
let (gas_price, buf) = unsafe { bytes::restore_number_unchecked(buf) };
let (gas_limit, buf) = unsafe { bytes::restore_number_unchecked(buf) };
let (maturity, buf) = unsafe { bytes::restore_number_unchecked(buf) };
let (_bytecode_length, buf) = unsafe { bytes::restore_u16_unchecked(buf) };
let (bytecode_witness_index, buf) = unsafe { bytes::restore_u8_unchecked(buf) };
let (static_contracts_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (inputs_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (outputs_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (witnesses_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (salt, mut buf) = unsafe { bytes::restore_array_unchecked(buf) };

let salt = salt.into();

Expand Down
86 changes: 86 additions & 0 deletions fuel-tx/src/transaction/types.rs
View file
Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
use crate::bytes;
use rand::distributions::{Distribution, Standard};
use rand::Rng;
use std::array::TryFromSliceError;
Expand All @@ -22,6 +23,27 @@ macro_rules! key {
pub const fn size_of() -> usize {
$s
}

/// Add a conversion from arbitrary slices into owned
///
/// # Warning
///
/// This function will not panic if the length of the slice is smaller than
/// `Self::size_of`. Instead, it will cause undefined behavior and read random disowned
/// bytes
pub unsafe fn from_slice_unchecked(bytes: &[u8]) -> Self {
$i(bytes::from_slice_unchecked(bytes))
}

/// Copy-free reference cast
pub unsafe fn as_ref_unchecked(bytes: &[u8]) -> &Self {
// The interpreter will frequently make references to keys and values using
// logically checked slices.
//
// This function will save unnecessary copy to owned slices for the interpreter
// access
&*(bytes.as_ptr() as *const Self)
}
}

impl rand::Fill for $i {
Expand Down Expand Up @@ -93,9 +115,73 @@ pub use witness::Witness;
key!(Address, 32);
key!(Color, 32);
key!(ContractId, 32);
key!(Bytes4, 4);
key!(Bytes8, 8);
key!(Bytes32, 32);
key!(Salt, 32);

impl ContractId {
pub const SEED: [u8; 4] = 0x4655454C_u32.to_be_bytes();
}

#[cfg(test)]
mod tests {
use crate::*;
use rand::rngs::StdRng;
use rand::{Rng, RngCore, SeedableRng};
use std::convert::TryFrom;

macro_rules! check_consistency {
($i:ident,$r:expr,$b:expr) => {
unsafe {
let n = $i::size_of();
let s = $r.gen_range(0..$b.len() - n);
let e = $r.gen_range(s + n..$b.len());
let r = $r.gen_range(1..n - 1);
let i = &$b[s..s + n];

let a = $i::from_slice_unchecked(i);
let b = $i::from_slice_unchecked(&$b[s..e]);
let c = $i::try_from(i).expect("Memory conversion");

// `d` will create random smaller slices and expect the value to be parsed correctly
//
// However, this is not the expected usage of the function
let d = $i::from_slice_unchecked(&i[..i.len() - r]);

let e = $i::as_ref_unchecked(i);

// Assert `from_slice_unchecked` will not create two references to the same owned
// memory
assert_ne!(a.as_ptr(), b.as_ptr());

// Assert `as_ref_unchecked` is copy-free
assert_ne!(e.as_ptr(), a.as_ptr());
assert_eq!(e.as_ptr(), i.as_ptr());

assert_eq!(a, b);
assert_eq!(a, c);
assert_eq!(a, d);
assert_eq!(&a, e);
}
};
}

#[test]
fn from_slice_unchecked_safety() {
let rng = &mut StdRng::seed_from_u64(8586);

let mut bytes = [0u8; 257];
rng.fill_bytes(&mut bytes);

for _ in 0..100 {
check_consistency!(Address, rng, bytes);
check_consistency!(Color, rng, bytes);
check_consistency!(ContractId, rng, bytes);
check_consistency!(Bytes4, rng, bytes);
check_consistency!(Bytes8, rng, bytes);
check_consistency!(Bytes32, rng, bytes);
check_consistency!(Salt, rng, bytes);
}
}
}
29 changes: 16 additions & 13 deletions fuel-tx/src/transaction/types/input.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -232,7 +232,8 @@ impl io::Write for Input {
return Err(bytes::eof());
}

let (identifier, buf): (Word, _) = bytes::restore_number_unchecked(buf);
// Safety: buf len is checked
let (identifier, buf): (Word, _) = unsafe { bytes::restore_number_unchecked(buf) };
let identifier = InputRepr::try_from(identifier)?;

match identifier {
Expand All @@ -241,15 +242,16 @@ impl io::Write for Input {
InputRepr::Coin => {
let mut n = INPUT_COIN_FIXED_SIZE;

let (utxo_id, buf) = bytes::restore_array_unchecked(buf);
let (owner, buf) = bytes::restore_array_unchecked(buf);
let (amount, buf) = bytes::restore_number_unchecked(buf);
let (color, buf) = bytes::restore_array_unchecked(buf);
let (witness_index, buf) = bytes::restore_u8_unchecked(buf);
let (maturity, buf) = bytes::restore_number_unchecked(buf);
// Safety: buf len is checked
let (utxo_id, buf) = unsafe { bytes::restore_array_unchecked(buf) };
let (owner, buf) = unsafe { bytes::restore_array_unchecked(buf) };
let (amount, buf) = unsafe { bytes::restore_number_unchecked(buf) };
let (color, buf) = unsafe { bytes::restore_array_unchecked(buf) };
let (witness_index, buf) = unsafe { bytes::restore_u8_unchecked(buf) };
let (maturity, buf) = unsafe { bytes::restore_number_unchecked(buf) };

let (predicate_len, buf) = bytes::restore_usize_unchecked(buf);
let (predicate_data_len, buf) = bytes::restore_usize_unchecked(buf);
let (predicate_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };
let (predicate_data_len, buf) = unsafe { bytes::restore_usize_unchecked(buf) };

let (size, predicate, buf) = bytes::restore_raw_bytes(buf, predicate_len)?;
n += size;
Expand Down Expand Up @@ -278,10 +280,11 @@ impl io::Write for Input {
InputRepr::Contract if buf.len() < INPUT_CONTRACT_SIZE - WORD_SIZE => Err(bytes::eof()),

InputRepr::Contract => {
let (utxo_id, buf) = bytes::restore_array_unchecked(buf);
let (balance_root, buf) = bytes::restore_array_unchecked(buf);
let (state_root, buf) = bytes::restore_array_unchecked(buf);
let (contract_id, _) = bytes::restore_array_unchecked(buf);
// Safety: checked buffer len
let (utxo_id, buf) = unsafe { bytes::restore_array_unchecked(buf) };
let (balance_root, buf) = unsafe { bytes::restore_array_unchecked(buf) };
let (state_root, buf) = unsafe { bytes::restore_array_unchecked(buf) };
let (contract_id, _) = unsafe { bytes::restore_array_unchecked(buf) };

let utxo_id = utxo_id.into();
let balance_root = balance_root.into();
Expand Down
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