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hashx: Rust hook for inspecting and modifying the random number stream

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This patch has no effect on the C tor build.

Adds a function hashx_rng_callback() to the hashx API, defined only
when HASHX_RNG_CALLBACK is defined. This is then used in the Rust
wrapper to implement a similar rng_callback().

Included some minimal test cases. This code is intented for
use in cross-compatibility fuzzing tests which drive multiple
implementations of hashx with the same custom Rng stream.

Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This commit is contained in:
Micah Elizabeth Scott 2023-07-28 19:44:24 -07:00
parent 4667195ded
commit 0ca2e62b28
9 changed files with 156 additions and 16 deletions
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2
src/ext/equix/Cargo.toml
View File

@ -9,7 +9,7 @@
[package]
name = "tor-c-equix"
version = "0.1.0"
version = "0.2.0"
edition = "2021"
license = "LGPL-3.0-only"

3
src/ext/equix/build.rs
View File

@ -16,6 +16,8 @@ fn main() {
"hashx/src/siphash_rng.c",
"hashx/src/virtual_memory.c",
])
// Activate our patch for hashx_rng_callback
.define("HASHX_RNG_CALLBACK", "1")
// Equi-X always uses HashX size 8 (64-bit output)
.define("HASHX_SIZE", "8")
// Avoid shared library API declarations, link statically
@ -31,6 +33,7 @@ fn main() {
.header_contents(
"wrapper.h",
r#"
#define HASHX_RNG_CALLBACK 1
#define HASHX_SIZE 8
#define HASHX_SHARED 1
#define EQUIX_SHARED 1

19
src/ext/equix/hashx/include/hashx.h
View File

@ -169,6 +169,25 @@ HASHX_API hashx_result hashx_exec(const hashx_ctx* ctx,
*/
HASHX_API void hashx_free(hashx_ctx* ctx);
#ifdef HASHX_RNG_CALLBACK
/*
* Set a callback for inspecting or modifying the HashX random number stream.
*
* The callback and its user pointer are associated with the provided context
* even if it's re-used for another hash program. A callback value of NULL
* disables the callback.
*
* @param ctx is pointer to a HashX instance.
* @param callback is invoked after each new 64-bit pseudorandom value
* is generated in a buffer. The callback may record it and/or replace
* it. A NULL pointer here disables the callback.
* @param user_data is an opaque parameter given to the callback
*/
HASHX_API void hashx_rng_callback(hashx_ctx* ctx,
void (*callback)(uint64_t*, void*),
void* user_data);
#endif
#ifdef __cplusplus
}
#endif

10
src/ext/equix/hashx/src/context.c
View File

@ -55,3 +55,13 @@ void hashx_free(hashx_ctx* ctx) {
free(ctx);
}
}
#ifdef HASHX_RNG_CALLBACK
void hashx_rng_callback(hashx_ctx* ctx,
void (*callback)(uint64_t*, void*),
void* callback_user_data)
{
ctx->program.rng_callback = callback;
ctx->program.rng_callback_user_data = callback_user_data;
}
#endif

4
src/ext/equix/hashx/src/program.c
View File

@ -554,6 +554,10 @@ bool hashx_program_generate(const siphash_state* key, hashx_program* program) {
.ports = {{ 0 }}
};
hashx_siphash_rng_init(&ctx.gen, key);
#ifdef HASHX_RNG_CALLBACK
ctx.gen.callback = program->rng_callback;
ctx.gen.callback_user_data = program->rng_callback_user_data;
#endif
for (int i = 0; i < 8; ++i) {
ctx.registers[i].last_op = -1;
ctx.registers[i].latency = 0;

4
src/ext/equix/hashx/src/program.h
View File

@ -29,6 +29,10 @@ typedef struct hashx_program {
int branch_count;
int branches[16];
#endif
#ifdef HASHX_RNG_CALLBACK
void (*rng_callback)(uint64_t *buffer, void *user_data);
void *rng_callback_user_data;
#endif
} hashx_program;
#ifdef __cplusplus

10
src/ext/equix/hashx/src/siphash_rng.c
View File

@ -15,6 +15,11 @@ uint8_t hashx_siphash_rng_u8(siphash_rng* gen) {
gen->buffer8 = hashx_siphash13_ctr(gen->counter, &gen->keys);
gen->counter++;
gen->count8 = sizeof(gen->buffer8);
#ifdef HASHX_RNG_CALLBACK
if (gen->callback) {
gen->callback(&gen->buffer8, gen->callback_user_data);
}
#endif
}
gen->count8--;
return gen->buffer8 >> (gen->count8 * 8);
@ -25,6 +30,11 @@ uint32_t hashx_siphash_rng_u32(siphash_rng* gen) {
gen->buffer32 = hashx_siphash13_ctr(gen->counter, &gen->keys);
gen->counter++;
gen->count32 = sizeof(gen->buffer32) / sizeof(uint32_t);
#ifdef HASHX_RNG_CALLBACK
if (gen->callback) {
gen->callback(&gen->buffer32, gen->callback_user_data);
}
#endif
}
gen->count32--;
return (uint32_t)(gen->buffer32 >> (gen->count32 * 32));

4
src/ext/equix/hashx/src/siphash_rng.h
View File

@ -13,6 +13,10 @@ typedef struct siphash_rng {
uint64_t counter;
uint64_t buffer8, buffer32;
unsigned count8, count32;
#ifdef HASHX_RNG_CALLBACK
void (*callback)(uint64_t *buffer, void *user_data);
void *callback_user_data;
#endif
} siphash_rng;
#ifdef __cplusplus

116
src/ext/equix/src/lib.rs
View File

@ -12,6 +12,10 @@
//! See `LICENSE` for licensing information.
//!
use core::ffi::c_void;
use core::mem;
use core::ptr::null_mut;
pub mod ffi {
//! Low-level access to the C API
@ -34,8 +38,14 @@ pub const HASHX_SIZE: usize = ffi::HASHX_SIZE as usize;
/// Output value obtained by executing a HashX hash function
pub type HashXOutput = [u8; HASHX_SIZE];
/// Type for callback functions that inspect or replace the pseudorandom stream
pub type RngCallback = Box<dyn FnMut(u64) -> u64>;
/// Safe wrapper around a HashX context
pub struct HashX(*mut ffi::hashx_ctx);
pub struct HashX {
ctx: *mut ffi::hashx_ctx,
rng_callback: Option<RngCallback>,
}
impl HashX {
/// Allocate a new HashX context
@ -44,7 +54,10 @@ impl HashX {
if ctx.is_null() {
panic!("out of memory in hashx_alloc");
}
Self(ctx)
Self {
ctx,
rng_callback: None,
}
}
/// Create a new hash function within this context, using the given seed
@ -53,14 +66,15 @@ impl HashX {
/// error occurs while the interpreter is disabled.
#[inline(always)]
pub fn make(&mut self, seed: &[u8]) -> HashXResult {
unsafe { ffi::hashx_make(self.0, seed.as_ptr() as *const std::ffi::c_void, seed.len()) }
unsafe { ffi::hashx_make(self.ctx, seed.as_ptr() as *const c_void, seed.len()) }
}
/// Check which implementation was selected by `make`
#[inline(always)]
pub fn query_type(&mut self) -> Result<HashXType, HashXResult> {
let mut buffer = HashXType::HASHX_TYPE_INTERPRETED; // Arbitrary default
let result = unsafe { ffi::hashx_query_type(self.0, &mut buffer as *mut ffi::hashx_type) };
let result =
unsafe { ffi::hashx_query_type(self.ctx, &mut buffer as *mut ffi::hashx_type) };
match result {
HashXResult::HASHX_OK => Ok(buffer),
e => Err(e),
@ -71,23 +85,45 @@ impl HashX {
#[inline(always)]
pub fn exec(&mut self, input: u64) -> Result<HashXOutput, HashXResult> {
let mut buffer: HashXOutput = Default::default();
let result = unsafe {
ffi::hashx_exec(
self.0,
input,
&mut buffer as *mut u8 as *mut std::ffi::c_void,
)
};
let result =
unsafe { ffi::hashx_exec(self.ctx, input, &mut buffer as *mut u8 as *mut c_void) };
match result {
HashXResult::HASHX_OK => Ok(buffer),
e => Err(e),
}
}
/// Set a callback function that may inspect and/or modify the internal
/// pseudorandom number stream used by this context.
///
/// The function will be owned by this context, and it replaces any
/// previous function that may have been set. Returns the previous callback
/// if any.
pub fn rng_callback(&mut self, callback: Option<RngCallback>) -> Option<RngCallback> {
// Keep ownership of our Rust value in the context wrapper, to match
// the lifetime of the mutable pointer that the C API saves.
let result = mem::replace(&mut self.rng_callback, callback);
match &mut self.rng_callback {
None => unsafe { ffi::hashx_rng_callback(self.ctx, None, null_mut()) },
Some(callback) => unsafe {
ffi::hashx_rng_callback(
self.ctx,
Some(wrapper),
callback as *mut RngCallback as *mut c_void,
);
},
}
unsafe extern "C" fn wrapper(buffer: *mut u64, callback: *mut c_void) {
let callback: &mut RngCallback = unsafe { mem::transmute(callback) };
buffer.write(callback(buffer.read()));
}
result
}
}
impl Drop for HashX {
fn drop(&mut self) {
let ctx = std::mem::replace(&mut self.0, std::ptr::null_mut());
let ctx = mem::replace(&mut self.ctx, null_mut());
unsafe {
ffi::hashx_free(ctx);
}
@ -146,7 +182,7 @@ impl EquiX {
unsafe {
ffi::equix_verify(
self.0,
challenge.as_ptr() as *const std::ffi::c_void,
challenge.as_ptr() as *const c_void,
challenge.len(),
solution as *const ffi::equix_solution,
)
@ -159,7 +195,7 @@ impl EquiX {
unsafe {
ffi::equix_solve(
self.0,
challenge.as_ptr() as *const std::ffi::c_void,
challenge.as_ptr() as *const c_void,
challenge.len(),
buffer as *mut ffi::equix_solutions_buffer,
)
@ -169,7 +205,7 @@ impl EquiX {
impl Drop for EquiX {
fn drop(&mut self) {
let ctx = std::mem::replace(&mut self.0, std::ptr::null_mut());
let ctx = mem::replace(&mut self.0, null_mut());
unsafe {
ffi::equix_free(ctx);
}
@ -180,6 +216,8 @@ impl Drop for EquiX {
mod tests {
use crate::*;
use hex_literal::hex;
use std::cell::RefCell;
use std::sync::Arc;
#[test]
fn equix_context() {
@ -290,4 +328,52 @@ mod tests {
assert_eq!(ctx.exec(123456), Ok(hex!("ab3d155bf4bbb0aa")));
assert_eq!(ctx.exec(987654321123456789), Ok(hex!("8dfef0497c323274")));
}
#[test]
fn rng_callback_read() {
// Use a Rng callback to read the sequence of pseudorandom numbers
// without changing them, and spot check the list we get back.
let mut ctx = HashX::new(HashXType::HASHX_TRY_COMPILE);
let seq = Arc::new(RefCell::new(Vec::new()));
{
let seq = seq.clone();
ctx.rng_callback(Some(Box::new(move |value| {
seq.borrow_mut().push(value);
value
})));
}
assert_eq!(seq.borrow().len(), 0);
assert_eq!(ctx.make(b"abc"), HashXResult::HASHX_OK);
assert_eq!(ctx.exec(12345).unwrap(), hex!("c0bc95da7cc30f37"));
assert_eq!(seq.borrow().len(), 563);
assert_eq!(
seq.borrow()[..4],
[
0xf695edd02205449d,
0x51c1ac51cd19a7d1,
0xadf4cb303b9814cf,
0x79793a52d965083d
]
);
}
#[test]
fn rng_callback_replace() {
// Use a Rng callback to replace the random number stream.
// We have to choose the replacement somewhat carefully since
// many stationary replacement values will cause infinite loops.
let mut ctx = HashX::new(HashXType::HASHX_TYPE_INTERPRETED);
let counter = Arc::new(RefCell::new(0u32));
{
let counter = counter.clone();
ctx.rng_callback(Some(Box::new(move |_value| {
*counter.borrow_mut() += 1;
0x0807060504030201
})));
}
assert_eq!(*counter.borrow(), 0);
assert_eq!(ctx.make(b"abc"), HashXResult::HASHX_OK);
assert_eq!(ctx.exec(12345).unwrap(), hex!("825a9b6dd5d074af"));
assert_eq!(*counter.borrow(), 575);
}
}