Revert to using RtlGenRandom as a fallback

library/std/src/sys/windows/c.rs

@@ -295,8 +295,6 @@ pub fn nt_success(status: NTSTATUS) -> bool {
     status >= 0
 }
 
-// "RNG\0"
-pub const BCRYPT_RNG_ALGORITHM: &[u16] = &[b'R' as u16, b'N' as u16, b'G' as u16, 0];
 pub const BCRYPT_USE_SYSTEM_PREFERRED_RNG: DWORD = 0x00000002;
 
 #[repr(C)]
@@ -834,6 +832,10 @@ if #[cfg(not(target_vendor = "uwp"))] {
 
     #[link(name = "advapi32")]
     extern "system" {
+        // Forbidden when targeting UWP
+        #[link_name = "SystemFunction036"]
+        pub fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: ULONG) -> BOOLEAN;
+
         // Allowed but unused by UWP
         pub fn OpenProcessToken(
             ProcessHandle: HANDLE,
@@ -1258,13 +1260,6 @@ extern "system" {
         cbBuffer: ULONG,
         dwFlags: ULONG,
     ) -> NTSTATUS;
-    pub fn BCryptOpenAlgorithmProvider(
-        phalgorithm: *mut BCRYPT_ALG_HANDLE,
-        pszAlgId: LPCWSTR,
-        pszimplementation: LPCWSTR,
-        dwflags: ULONG,
-    ) -> NTSTATUS;
-    pub fn BCryptCloseAlgorithmProvider(hAlgorithm: BCRYPT_ALG_HANDLE, dwFlags: ULONG) -> NTSTATUS;
 }
 
 // Functions that aren't available on every version of Windows that we support,

library/std/src/sys/windows/rand.rs

@@ -1,106 +1,39 @@
-//! # Random key generation
-//!
-//! This module wraps the RNG provided by the OS. There are a few different
-//! ways to interface with the OS RNG so it's worth exploring each of the options.
-//! Note that at the time of writing these all go through the (undocumented)
-//! `bcryptPrimitives.dll` but they use different route to get there.
-//!
-//! Originally we were using [`RtlGenRandom`], however that function is
-//! deprecated and warns it "may be altered or unavailable in subsequent versions".
-//!
-//! So we switched to [`BCryptGenRandom`] with the `BCRYPT_USE_SYSTEM_PREFERRED_RNG`
-//! flag to query and find the system configured RNG. However, this change caused a small
-//! but significant number of users to experience panics caused by a failure of
-//! this function. See [#94098].
-//!
-//! The current version falls back to using `BCryptOpenAlgorithmProvider` if
-//! `BCRYPT_USE_SYSTEM_PREFERRED_RNG` fails for any reason.
-//!
-//! [#94098]: /~https://github.com/rust-lang/rust/issues/94098
-//! [`RtlGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
-//! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
+use crate::io;
 use crate::mem;
 use crate::ptr;
 use crate::sys::c;
 
-/// Generates high quality secure random keys for use by [`HashMap`].
-///
-/// This is used to seed the default [`RandomState`].
-///
-/// [`HashMap`]: crate::collections::HashMap
-/// [`RandomState`]: crate::collections::hash_map::RandomState
 pub fn hashmap_random_keys() -> (u64, u64) {
-    Rng::SYSTEM.gen_random_keys().unwrap_or_else(fallback_rng)
+    let mut v = (0, 0);
+    let ret = unsafe {
+        c::BCryptGenRandom(
+            ptr::null_mut(),
+            &mut v as *mut _ as *mut u8,
+            mem::size_of_val(&v) as c::ULONG,
+            c::BCRYPT_USE_SYSTEM_PREFERRED_RNG,
+        )
+    };
+    if c::nt_success(ret) { v } else { fallback_rng() }
 }
 
-struct Rng {
-    algorithm: c::BCRYPT_ALG_HANDLE,
-    flags: u32,
-}
-impl Rng {
-    const SYSTEM: Self = unsafe { Self::new(ptr::null_mut(), c::BCRYPT_USE_SYSTEM_PREFERRED_RNG) };
-
-    /// Create the RNG from an existing algorithm handle.
-    ///
-    /// # Safety
-    ///
-    /// The handle must either be null or a valid algorithm handle.
-    const unsafe fn new(algorithm: c::BCRYPT_ALG_HANDLE, flags: u32) -> Self {
-        Self { algorithm, flags }
-    }
-
-    /// Open a handle to the RNG algorithm.
-    fn open() -> Result<Self, c::NTSTATUS> {
-        use crate::sync::atomic::AtomicPtr;
-        use crate::sync::atomic::Ordering::{Acquire, Release};
-
-        // An atomic is used so we don't need to reopen the handle every time.
-        static HANDLE: AtomicPtr<crate::ffi::c_void> = AtomicPtr::new(ptr::null_mut());
-
-        let mut handle = HANDLE.load(Acquire);
-        if handle.is_null() {
-            let status = unsafe {
-                c::BCryptOpenAlgorithmProvider(
-                    &mut handle,
-                    c::BCRYPT_RNG_ALGORITHM.as_ptr(),
-                    ptr::null(),
-                    0,
-                )
-            };
-            if c::nt_success(status) {
-                // If another thread opens a handle first then use that handle instead.
-                let result = HANDLE.compare_exchange(ptr::null_mut(), handle, Release, Acquire);
-                if let Err(previous_handle) = result {
-                    // Close our handle and return the previous one.
-                    unsafe { c::BCryptCloseAlgorithmProvider(handle, 0) };
-                    handle = previous_handle;
-                }
-                Ok(unsafe { Self::new(handle, 0) })
-            } else {
-                Err(status)
-            }
-        } else {
-            Ok(unsafe { Self::new(handle, 0) })
-        }
-    }
+/// Generate random numbers using the fallback RNG function (RtlGenRandom)
+///
+/// This is necessary because of a failure to load the SysWOW64 variant of the
+/// bcryptprimitives.dll library from code that lives in bcrypt.dll
+/// See <https://bugzilla.mozilla.org/show_bug.cgi?id=1788004#c9>
+#[cfg(not(target_vendor = "uwp"))]
+#[inline(never)]
+fn fallback_rng() -> (u64, u64) {
+    let mut v = (0, 0);
+    let ret =
+        unsafe { c::RtlGenRandom(&mut v as *mut _ as *mut u8, mem::size_of_val(&v) as c::ULONG) };
 
-    fn gen_random_keys(self) -> Result<(u64, u64), c::NTSTATUS> {
-        let mut v = (0, 0);
-        let status = unsafe {
-            let size = mem::size_of_val(&v).try_into().unwrap();
-            c::BCryptGenRandom(self.algorithm, ptr::addr_of_mut!(v).cast(), size, self.flags)
-        };
-        if c::nt_success(status) { Ok(v) } else { Err(status) }
-    }
+    if ret != 0 { v } else { panic!("fallback RNG broken: {}", io::Error::last_os_error()) }
 }
 
-/// Generate random numbers using the fallback RNG function
+/// We can't use RtlGenRandom with UWP, so there is no fallback
+#[cfg(target_vendor = "uwp")]
 #[inline(never)]
-fn fallback_rng(rng_status: c::NTSTATUS) -> (u64, u64) {
-    match Rng::open().and_then(|rng| rng.gen_random_keys()) {
-        Ok(keys) => keys,
-        Err(status) => {
-            panic!("RNG broken: {rng_status:#x}, fallback RNG broken: {status:#x}")
-        }
-    }
+fn fallback_rng() -> (u64, u64) {
+    panic!("fallback RNG broken: RtlGenRandom() not supported on UWP");
 }