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Unify lazy atomics in entropy backends #804

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18 changes: 8 additions & 10 deletions src/backends/efi_rng.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,7 @@
use crate::Error;
use core::{
mem::MaybeUninit,
ptr::{self, NonNull, null_mut},
sync::atomic::{AtomicPtr, Ordering::Relaxed},
ptr::{self, NonNull},
};
use r_efi::{
efi::{BootServices, Handle},
Expand All @@ -17,8 +16,6 @@ pub use crate::util::{inner_u32, inner_u64};
#[cfg(not(target_os = "uefi"))]
compile_error!("`efi_rng` backend can be enabled only for UEFI targets!");

static RNG_PROTOCOL: AtomicPtr<rng::Protocol> = AtomicPtr::new(null_mut());

#[cold]
#[inline(never)]
fn init() -> Result<NonNull<rng::Protocol>, Error> {
Expand All @@ -36,7 +33,7 @@ fn init() -> Result<NonNull<rng::Protocol>, Error> {
((*boot_services.as_ptr()).locate_handle)(
r_efi::efi::BY_PROTOCOL,
&mut guid,
null_mut(),
ptr::null_mut(),
&mut buf_size,
handles.as_mut_ptr(),
)
Expand Down Expand Up @@ -88,18 +85,19 @@ fn init() -> Result<NonNull<rng::Protocol>, Error> {
continue;
}

RNG_PROTOCOL.store(protocol.as_ptr(), Relaxed);
return Ok(protocol);
}
Err(Error::NO_RNG_HANDLE)
}

#[inline]
pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
let protocol = match NonNull::new(RNG_PROTOCOL.load(Relaxed)) {
Some(p) => p,
None => init()?,
};
#[path = "../utils/lazy.rs"]
mod lazy;

static RNG_PROTOCOL: lazy::LazyNonNull<rng::Protocol> = lazy::LazyNonNull::new();

let protocol = RNG_PROTOCOL.try_unsync_init(init)?;

let mut alg_guid = rng::ALGORITHM_RAW;
let ret = unsafe {
Expand Down
37 changes: 11 additions & 26 deletions src/backends/linux_android_with_fallback.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,7 @@ use crate::Error;
use core::{
ffi::c_void,
mem::{MaybeUninit, transmute},
ptr::NonNull,
sync::atomic::{AtomicPtr, Ordering},
ptr::{self, NonNull},
};
use use_file::utils;

Expand All @@ -15,20 +14,14 @@ type GetRandomFn = unsafe extern "C" fn(*mut c_void, libc::size_t, libc::c_uint)

/// Sentinel value which indicates that `libc::getrandom` either not available,
/// or not supported by kernel.
const NOT_AVAILABLE: NonNull<c_void> = unsafe { NonNull::new_unchecked(usize::MAX as *mut c_void) };

static GETRANDOM_FN: AtomicPtr<c_void> = AtomicPtr::new(core::ptr::null_mut());
const NOT_AVAILABLE: NonNull<c_void> = NonNull::dangling();

#[cold]
#[inline(never)]
fn init() -> NonNull<c_void> {
// Use static linking to `libc::getrandom` on MUSL targets and `dlsym` everywhere else
#[cfg(not(target_env = "musl"))]
let raw_ptr = {
static NAME: &[u8] = b"getrandom\0";
let name_ptr = NAME.as_ptr().cast::<libc::c_char>();
unsafe { libc::dlsym(libc::RTLD_DEFAULT, name_ptr) }
};
let raw_ptr = unsafe { libc::dlsym(libc::RTLD_DEFAULT, c"getrandom".as_ptr()) };
#[cfg(target_env = "musl")]
let raw_ptr = {
let fptr: GetRandomFn = libc::getrandom;
Expand All @@ -37,10 +30,9 @@ fn init() -> NonNull<c_void> {

let res_ptr = match NonNull::new(raw_ptr) {
Some(fptr) => {
let getrandom_fn = unsafe { transmute::<NonNull<c_void>, GetRandomFn>(fptr) };
let dangling_ptr = NonNull::dangling().as_ptr();
let getrandom_fn = unsafe { transmute::<*mut c_void, GetRandomFn>(fptr.as_ptr()) };
// Check that `getrandom` syscall is supported by kernel
let res = unsafe { getrandom_fn(dangling_ptr, 0, 0) };
let res = unsafe { getrandom_fn(ptr::dangling_mut(), 0, 0) };
if cfg!(getrandom_test_linux_fallback) {
NOT_AVAILABLE
} else if res.is_negative() {
Expand All @@ -65,7 +57,6 @@ fn init() -> NonNull<c_void> {
panic!("Fallback is triggered with enabled `getrandom_test_linux_without_fallback`")
}

GETRANDOM_FN.store(res_ptr.as_ptr(), Ordering::Release);
res_ptr
}

Expand All @@ -77,23 +68,17 @@ fn use_file_fallback(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {

#[inline]
pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
// Despite being only a single atomic variable, we still cannot always use
// Ordering::Relaxed, as we need to make sure a successful call to `init`
// is "ordered before" any data read through the returned pointer (which
// occurs when the function is called). Our implementation mirrors that of
// the one in libstd, meaning that the use of non-Relaxed operations is
// probably unnecessary.
let raw_ptr = GETRANDOM_FN.load(Ordering::Acquire);
let fptr = match NonNull::new(raw_ptr) {
Some(p) => p,
None => init(),
};
#[path = "../utils/lazy.rs"]
mod lazy;

static GETRANDOM_FN: lazy::LazyNonNull<c_void> = lazy::LazyNonNull::new();
let fptr = GETRANDOM_FN.unsync_init(init);

if fptr == NOT_AVAILABLE {
use_file_fallback(dest)
} else {
// note: `transmute` is currently the only way to convert a pointer into a function reference
let getrandom_fn = unsafe { transmute::<NonNull<c_void>, GetRandomFn>(fptr) };
let getrandom_fn = unsafe { transmute::<*mut c_void, GetRandomFn>(fptr.as_ptr()) };
utils::sys_fill_exact(dest, |buf| unsafe {
getrandom_fn(buf.as_mut_ptr().cast(), buf.len(), 0)
})
Expand Down
41 changes: 16 additions & 25 deletions src/backends/netbsd.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,8 +8,7 @@ use core::{
cmp,
ffi::c_void,
mem::{self, MaybeUninit},
ptr,
sync::atomic::{AtomicPtr, Ordering},
ptr::{self, NonNull},
};

pub use crate::util::{inner_u32, inner_u64};
Expand Down Expand Up @@ -42,36 +41,28 @@ unsafe extern "C" fn polyfill_using_kern_arand(

type GetRandomFn = unsafe extern "C" fn(*mut c_void, libc::size_t, libc::c_uint) -> libc::ssize_t;

static GETRANDOM: AtomicPtr<c_void> = AtomicPtr::new(ptr::null_mut());

#[cold]
#[inline(never)]
fn init() -> *mut c_void {
static NAME: &[u8] = b"getrandom\0";
let name_ptr = NAME.as_ptr().cast::<libc::c_char>();
let mut ptr = unsafe { libc::dlsym(libc::RTLD_DEFAULT, name_ptr) };
if ptr.is_null() || cfg!(getrandom_test_netbsd_fallback) {
// Verify `polyfill_using_kern_arand` has the right signature.
const POLYFILL: GetRandomFn = polyfill_using_kern_arand;
ptr = POLYFILL as *mut c_void;
fn init() -> NonNull<c_void> {
let ptr = unsafe { libc::dlsym(libc::RTLD_DEFAULT, c"getrandom".as_ptr()) };
if !cfg!(getrandom_test_netbsd_fallback) {
if let Some(ptr) = NonNull::new(ptr) {
return ptr;
}
}
GETRANDOM.store(ptr, Ordering::Release);
ptr
const POLYFILL: GetRandomFn = polyfill_using_kern_arand;
unsafe { NonNull::new_unchecked(POLYFILL as *mut c_void) }
}

#[inline]
pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
// Despite being only a single atomic variable, we still cannot always use
// Ordering::Relaxed, as we need to make sure a successful call to `init`
// is "ordered before" any data read through the returned pointer (which
// occurs when the function is called). Our implementation mirrors that of
// the one in libstd, meaning that the use of non-Relaxed operations is
// probably unnecessary.
let mut fptr = GETRANDOM.load(Ordering::Acquire);
if fptr.is_null() {
fptr = init();
}
let fptr = unsafe { mem::transmute::<*mut c_void, GetRandomFn>(fptr) };
#[path = "../utils/lazy.rs"]
mod lazy;

static GETRANDOM_FN: lazy::LazyNonNull<c_void> = lazy::LazyNonNull::new();

let fptr = GETRANDOM_FN.unsync_init(init);
let fptr = unsafe { mem::transmute::<*mut c_void, GetRandomFn>(fptr.as_ptr()) };
utils::sys_fill_exact(dest, |buf| unsafe {
fptr(buf.as_mut_ptr().cast::<c_void>(), buf.len(), 0)
})
Expand Down
24 changes: 15 additions & 9 deletions src/backends/rdrand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,9 +2,6 @@
use crate::{Error, util::slice_as_uninit};
use core::mem::{MaybeUninit, size_of};

#[path = "../utils/lazy.rs"]
mod lazy;

#[cfg(not(any(target_arch = "x86_64", target_arch = "x86")))]
compile_error!("`rdrand` backend can be enabled only for x86 and x86-64 targets!");

Expand All @@ -20,8 +17,6 @@ cfg_if! {
}
}

static RDRAND_GOOD: lazy::LazyBool = lazy::LazyBool::new();

// Recommendation from "Intel® Digital Random Number Generator (DRNG) Software
// Implementation Guide" - Section 5.2.1 and "Intel® 64 and IA-32 Architectures
// Software Developer’s Manual" - Volume 1 - Section 7.3.17.1.
Expand Down Expand Up @@ -72,7 +67,9 @@ fn self_test() -> bool {
fails <= 2
}

fn is_rdrand_good() -> bool {
#[cold]
#[inline(never)]
fn init() -> bool {
#[cfg(not(target_feature = "rdrand"))]
{
// SAFETY: All Rust x86 targets are new enough to have CPUID, and we
Expand Down Expand Up @@ -115,6 +112,15 @@ fn is_rdrand_good() -> bool {
unsafe { self_test() }
}

fn is_rdrand_good() -> bool {
#[path = "../utils/lazy.rs"]
mod lazy;

static RDRAND_GOOD: lazy::LazyBool = lazy::LazyBool::new();

RDRAND_GOOD.unsync_init(init)
}

#[target_feature(enable = "rdrand")]
fn rdrand_exact(dest: &mut [MaybeUninit<u8>]) -> Option<()> {
// We use chunks_exact_mut instead of chunks_mut as it allows almost all
Expand Down Expand Up @@ -162,7 +168,7 @@ fn rdrand_u64() -> Option<u64> {

#[inline]
pub fn inner_u32() -> Result<u32, Error> {
if !RDRAND_GOOD.unsync_init(is_rdrand_good) {
if !is_rdrand_good() {
return Err(Error::NO_RDRAND);
}
// SAFETY: After this point, we know rdrand is supported.
Expand All @@ -171,7 +177,7 @@ pub fn inner_u32() -> Result<u32, Error> {

#[inline]
pub fn inner_u64() -> Result<u64, Error> {
if !RDRAND_GOOD.unsync_init(is_rdrand_good) {
if !is_rdrand_good() {
return Err(Error::NO_RDRAND);
}
// SAFETY: After this point, we know rdrand is supported.
Expand All @@ -180,7 +186,7 @@ pub fn inner_u64() -> Result<u64, Error> {

#[inline]
pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
if !RDRAND_GOOD.unsync_init(is_rdrand_good) {
if !is_rdrand_good() {
return Err(Error::NO_RDRAND);
}
// SAFETY: After this point, we know rdrand is supported.
Expand Down
1 change: 1 addition & 0 deletions src/backends/rndr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,7 @@ fn is_rndr_available() -> bool {
fn is_rndr_available() -> bool {
#[path = "../utils/lazy.rs"]
mod lazy;

static RNDR_GOOD: lazy::LazyBool = lazy::LazyBool::new();

cfg_if::cfg_if! {
Expand Down
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