Add functions to generate random u32 and u64 values (#544)

These functions can be helpful for seed generation and implementation of
`OsRng`. Additionally, some backends (Hermit, RDRAND, RNDR, WASI p2) can
directly generate random `u32`/`u64` values. Relying on the byte API may
be less efficient in these cases.

Using `u32` and `u64` as function names may seem problematic, but based
on the `fasrand` experience, it works well in practice, provided that
users reference them as `getrandom::u32/u64` without importing them
directly.

src/backends.rs

@@ -116,8 +116,20 @@ cfg_if! {
         mod apple_other;
         pub use apple_other::*;
     } else if #[cfg(all(target_arch = "wasm32", target_os = "wasi"))] {
-        mod wasi;
-        pub use wasi::*;
+        cfg_if! {
+            if #[cfg(target_env = "p1")] {
+                mod wasi_p1;
+                pub use wasi_p1::*;
+            } else if #[cfg(target_env = "p2")] {
+                mod wasi_p2;
+                pub use wasi_p2::*;
+            } else {
+                compile_error!(
+                    "Unknown version of WASI (only previews 1 and 2 are supported) \
+                    or Rust version older than 1.80 was used"
+                );
+            }
+        }
     } else if #[cfg(target_os = "hermit")] {
         mod hermit;
         pub use hermit::*;

src/backends/apple_other.rs

@@ -2,6 +2,8 @@
 use crate::Error;
 use core::{ffi::c_void, mem::MaybeUninit};
 
+pub use crate::util::{inner_u32, inner_u64};
+
 pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
     let dst_ptr = dest.as_mut_ptr().cast::<c_void>();
     let ret = unsafe { libc::CCRandomGenerateBytes(dst_ptr, dest.len()) };

src/backends/custom.rs

@@ -2,6 +2,8 @@
 use crate::Error;
 use core::mem::MaybeUninit;
 
+pub use crate::util::{inner_u32, inner_u64};
+
 pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
     extern "Rust" {
         fn __getrandom_v03_custom(dest: *mut u8, len: usize) -> Result<(), Error>;

src/backends/esp_idf.rs

@@ -2,6 +2,8 @@
 use crate::Error;
 use core::{ffi::c_void, mem::MaybeUninit};
 
+pub use crate::util::{inner_u32, inner_u64};
+
 #[cfg(not(target_os = "espidf"))]
 compile_error!("`esp_idf` backend can be enabled only for ESP-IDF targets!");
 

src/backends/fuchsia.rs

@@ -2,6 +2,8 @@
 use crate::Error;
 use core::mem::MaybeUninit;
 
+pub use crate::util::{inner_u32, inner_u64};
+
 #[link(name = "zircon")]
 extern "C" {
     fn zx_cprng_draw(buffer: *mut u8, length: usize);

src/backends/getentropy.rs

@@ -10,6 +10,8 @@
 use crate::Error;
 use core::{ffi::c_void, mem::MaybeUninit};
 
+pub use crate::util::{inner_u32, inner_u64};
+
 #[path = "../util_libc.rs"]
 mod util_libc;
 

src/backends/getrandom.rs

@@ -18,6 +18,8 @@
 use crate::Error;
 use core::{ffi::c_void, mem::MaybeUninit};
 
+pub use crate::util::{inner_u32, inner_u64};
+
 #[path = "../util_libc.rs"]
 mod util_libc;
 

src/backends/hermit.rs

@@ -4,6 +4,32 @@ use core::mem::MaybeUninit;
 
 extern "C" {
     fn sys_read_entropy(buffer: *mut u8, length: usize, flags: u32) -> isize;
+    // Note that `sys_secure_rand32/64` are implemented using `sys_read_entropy`:
+    // https://github.com/hermit-os/kernel/blob/430da84/src/syscalls/entropy.rs#L62-L104
+    // But this may change in future and can depend on compilation target,
+    // so to future-proof we use these "syscalls".
+    fn sys_secure_rand32(value: *mut u32) -> i32;
+    fn sys_secure_rand64(value: *mut u64) -> i32;
+}
+
+pub fn inner_u32() -> Result<u32, Error> {
+    let mut res = MaybeUninit::uninit();
+    let ret = unsafe { sys_secure_rand32(res.as_mut_ptr()) };
+    match ret {
+        0 => Ok(unsafe { res.assume_init() }),
+        -1 => Err(Error::UNSUPPORTED),
+        _ => Err(Error::UNEXPECTED),
+    }
+}
+
+pub fn inner_u64() -> Result<u64, Error> {
+    let mut res = MaybeUninit::uninit();
+    let ret = unsafe { sys_secure_rand64(res.as_mut_ptr()) };
+    match ret {
+        0 => Ok(unsafe { res.assume_init() }),
+        -1 => Err(Error::UNSUPPORTED),
+        _ => Err(Error::UNEXPECTED),
+    }
 }
 
 pub fn fill_inner(mut dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {

src/backends/linux_android.rs

@@ -2,6 +2,8 @@
 use crate::Error;
 use core::mem::MaybeUninit;
 
+pub use crate::util::{inner_u32, inner_u64};
+
 #[path = "../util_libc.rs"]
 mod util_libc;
 

src/backends/linux_android_with_fallback.rs

@@ -9,6 +9,8 @@ use core::{
 };
 use use_file::util_libc;
 
+pub use crate::util::{inner_u32, inner_u64};
+
 type GetRandomFn = unsafe extern "C" fn(*mut c_void, libc::size_t, libc::c_uint) -> libc::ssize_t;
 
 /// Sentinel value which indicates that `libc::getrandom` either not available,

src/backends/linux_rustix.rs

@@ -2,6 +2,8 @@
 use crate::{Error, MaybeUninit};
 use rustix::rand::{getrandom_uninit, GetRandomFlags};
 
+pub use crate::util::{inner_u32, inner_u64};
+
 #[cfg(not(any(target_os = "android", target_os = "linux")))]
 compile_error!("`linux_rustix` backend can be enabled only for Linux/Android targets!");
 

src/backends/netbsd.rs

@@ -12,6 +12,8 @@ use core::{
     sync::atomic::{AtomicPtr, Ordering},
 };
 
+pub use crate::util::{inner_u32, inner_u64};
+
 #[path = "../util_libc.rs"]
 mod util_libc;
 

src/backends/rdrand.rs

@@ -20,6 +20,8 @@ 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.
@@ -99,15 +101,6 @@ fn is_rdrand_good() -> bool {
     unsafe { self_test() }
 }
 
-pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    static RDRAND_GOOD: lazy::LazyBool = lazy::LazyBool::new();
-    if !RDRAND_GOOD.unsync_init(is_rdrand_good) {
-        return Err(Error::NO_RDRAND);
-    }
-    // SAFETY: After this point, we know rdrand is supported.
-    unsafe { rdrand_exact(dest) }.ok_or(Error::FAILED_RDRAND)
-}
-
 // TODO: make this function safe when we have feature(target_feature_11)
 #[target_feature(enable = "rdrand")]
 unsafe fn rdrand_exact(dest: &mut [MaybeUninit<u8>]) -> Option<()> {
@@ -127,3 +120,53 @@ unsafe fn rdrand_exact(dest: &mut [MaybeUninit<u8>]) -> Option<()> {
     }
     Some(())
 }
+
+#[cfg(target_arch = "x86_64")]
+#[target_feature(enable = "rdrand")]
+unsafe fn rdrand_u32() -> Option<u32> {
+    rdrand().map(crate::util::truncate)
+}
+
+#[cfg(target_arch = "x86_64")]
+#[target_feature(enable = "rdrand")]
+unsafe fn rdrand_u64() -> Option<u64> {
+    rdrand()
+}
+
+#[cfg(target_arch = "x86")]
+#[target_feature(enable = "rdrand")]
+unsafe fn rdrand_u32() -> Option<u32> {
+    rdrand()
+}
+
+#[cfg(target_arch = "x86")]
+#[target_feature(enable = "rdrand")]
+unsafe fn rdrand_u64() -> Option<u64> {
+    let a = rdrand()?;
+    let b = rdrand()?;
+    Some((u64::from(a) << 32) || u64::from(b))
+}
+
+pub fn inner_u32() -> Result<u32, Error> {
+    if !RDRAND_GOOD.unsync_init(is_rdrand_good) {
+        return Err(Error::NO_RDRAND);
+    }
+    // SAFETY: After this point, we know rdrand is supported.
+    unsafe { rdrand_u32() }.ok_or(Error::FAILED_RDRAND)
+}
+
+pub fn inner_u64() -> Result<u64, Error> {
+    if !RDRAND_GOOD.unsync_init(is_rdrand_good) {
+        return Err(Error::NO_RDRAND);
+    }
+    // SAFETY: After this point, we know rdrand is supported.
+    unsafe { rdrand_u64() }.ok_or(Error::FAILED_RDRAND)
+}
+
+pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
+    if !RDRAND_GOOD.unsync_init(is_rdrand_good) {
+        return Err(Error::NO_RDRAND);
+    }
+    // SAFETY: After this point, we know rdrand is supported.
+    unsafe { rdrand_exact(dest) }.ok_or(Error::FAILED_RDRAND)
+}

src/backends/rndr.rs

@@ -2,7 +2,10 @@
 //!
 //! Arm Architecture Reference Manual for A-profile architecture:
 //! ARM DDI 0487K.a, ID032224, D23.2.147 RNDR, Random Number
-use crate::{util::slice_as_uninit, Error};
+use crate::{
+    util::{slice_as_uninit, truncate},
+    Error,
+};
 use core::arch::asm;
 use core::mem::{size_of, MaybeUninit};
 
@@ -101,6 +104,26 @@ fn is_rndr_available() -> bool {
     }
 }
 
+pub fn inner_u32() -> Result<u32, Error> {
+    if is_rndr_available() {
+        // SAFETY: after this point, we know the `rand` target feature is enabled
+        let res = unsafe { rndr() };
+        res.map(truncate).ok_or(Error::RNDR_FAILURE)
+    } else {
+        Err(Error::RNDR_NOT_AVAILABLE)
+    }
+}
+
+pub fn inner_u64() -> Result<u64, Error> {
+    if is_rndr_available() {
+        // SAFETY: after this point, we know the `rand` target feature is enabled
+        let res = unsafe { rndr() };
+        res.ok_or(Error::RNDR_FAILURE)
+    } else {
+        Err(Error::RNDR_NOT_AVAILABLE)
+    }
+}
+
 pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
     if is_rndr_available() {
         // SAFETY: after this point, we know the `rand` target feature is enabled

src/backends/solaris.rs

@@ -15,6 +15,8 @@
 use crate::Error;
 use core::{ffi::c_void, mem::MaybeUninit};
 
+pub use crate::util::{inner_u32, inner_u64};
+
 #[path = "../util_libc.rs"]
 mod util_libc;
 

src/backends/solid.rs

@@ -2,6 +2,8 @@
 use crate::Error;
 use core::mem::MaybeUninit;
 
+pub use crate::util::{inner_u32, inner_u64};
+
 extern "C" {
     pub fn SOLID_RNG_SampleRandomBytes(buffer: *mut u8, length: usize) -> i32;
 }

src/backends/use_file.rs

@@ -6,6 +6,9 @@ use core::{
     sync::atomic::{AtomicI32, Ordering},
 };
 
+#[cfg(not(any(target_os = "android", target_os = "linux")))]
+pub use crate::util::{inner_u32, inner_u64};
+
 #[path = "../util_libc.rs"]
 pub(super) mod util_libc;
 

src/backends/vxworks.rs

@@ -9,6 +9,8 @@ use core::{
 #[path = "../util_libc.rs"]
 mod util_libc;
 
+pub use crate::util::{inner_u32, inner_u64};
+
 pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
     static RNG_INIT: AtomicBool = AtomicBool::new(false);
     while !RNG_INIT.load(Relaxed) {