remove Windows XP support

Author: newpavlov

build.rs

@@ -4,12 +4,9 @@ use std::env;
 
 fn main() {
     let target = env::var("TARGET").expect("TARGET was not set");
-    if target.contains("-uwp-windows-") {
+    if target.contains("windows") {
         // for BCryptGenRandom
         println!("cargo:rustc-link-lib=bcrypt");
-    } else if target.contains("windows") {
-        // for RtlGenRandom (aka SystemFunction036)
-        println!("cargo:rustc-link-lib=advapi32");
     } else if target.contains("apple-ios") {
         // for SecRandomCopyBytes and kSecRandomDefault
         println!("cargo:rustc-link-lib=framework=Security");

src/lib.rs

@@ -13,8 +13,7 @@
 //! | Target            | Target Triple      | Implementation
 //! | ----------------- | ------------------ | --------------
 //! | Linux, Android    | `*‑linux‑*`        | [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after successfully polling `/dev/random` |
-//! | Windows           | `*‑pc‑windows‑*`   | [`RtlGenRandom`][3] |
-//! | [Windows UWP][22] | `*‑uwp‑windows‑*`  | [`BCryptGenRandom`][23] |
+//! | Windows           | `*‑pc‑windows‑*`   | [`BCryptGenRandom`][3] |
 //! | macOS             | `*‑apple‑darwin`   | [`getentropy()`][19] if available, otherwise [`/dev/random`][20] (identical to `/dev/urandom`)
 //! | iOS               | `*‑apple‑ios`      | [`SecRandomCopyBytes`][4]
 //! | FreeBSD           | `*‑freebsd`        | [`getrandom()`][21] if available, otherwise [`kern.arandom`][5]
@@ -123,7 +122,7 @@
 //!
 //! [1]: http://man7.org/linux/man-pages/man2/getrandom.2.html
 //! [2]: http://man7.org/linux/man-pages/man4/urandom.4.html
-//! [3]: https://docs.microsoft.com/en-us/windows/desktop/api/ntsecapi/nf-ntsecapi-rtlgenrandom
+//! [3]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
 //! [4]: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
 //! [5]: https://www.freebsd.org/cgi/man.cgi?query=random&sektion=4
 //! [6]: https://man.openbsd.org/getentropy.2
@@ -142,8 +141,6 @@
 //! [19]: https://www.unix.com/man-page/mojave/2/getentropy/
 //! [20]: https://www.unix.com/man-page/mojave/4/random/
 //! [21]: https://www.freebsd.org/cgi/man.cgi?query=getrandom&manpath=FreeBSD+12.0-stable
-//! [22]: https://docs.microsoft.com/en-us/windows/uwp/
-//! [23]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
 
 #![doc(
     html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
@@ -204,8 +201,6 @@ cfg_if! {
     } else if #[cfg(target_os = "vxworks")] {
         mod util_libc;
         #[path = "vxworks.rs"] mod imp;
-    } else if #[cfg(all(windows, target_vendor = "uwp"))] {
-        #[path = "windows_uwp.rs"] mod imp;
     } else if #[cfg(windows)] {
         #[path = "windows.rs"] mod imp;
     } else if #[cfg(all(target_arch = "x86_64", target_env = "sgx"))] {

src/windows.rs

@@ -6,20 +6,43 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! Implementation for Windows
+//! Implementation for Windows UWP targets. After deprecation of Windows XP
+//! and Vista, this can supersede the `RtlGenRandom`-based implementation.
 use crate::Error;
+use core::{ffi::c_void, num::NonZeroU32, ptr};
+
+const BCRYPT_USE_SYSTEM_PREFERRED_RNG: u32 = 0x00000002;
 
 extern "system" {
-    #[link_name = "SystemFunction036"]
-    fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: u32) -> u8;
+    fn BCryptGenRandom(
+        hAlgorithm: *mut c_void,
+        pBuffer: *mut u8,
+        cbBuffer: u32,
+        dwFlags: u32,
+    ) -> u32;
 }
 
 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
     // Prevent overflow of u32
     for chunk in dest.chunks_mut(u32::max_value() as usize) {
-        let ret = unsafe { RtlGenRandom(chunk.as_mut_ptr(), chunk.len() as u32) };
-        if ret == 0 {
-            return Err(Error::WINDOWS_RTL_GEN_RANDOM);
+        let ret = unsafe {
+            BCryptGenRandom(
+                ptr::null_mut(),
+                chunk.as_mut_ptr(),
+                chunk.len() as u32,
+                BCRYPT_USE_SYSTEM_PREFERRED_RNG,
+            )
+        };
+        // NTSTATUS codes use the two highest bits for severity status.
+        if ret >> 30 == 0b11 {
+            // We zeroize the highest bit, so the error code will reside
+            // inside the range designated for OS codes.
+            let code = ret ^ (1 << 31);
+            // SAFETY: the second highest bit is always equal to one,
+            // so it's impossible to get zero. Unfortunately the type
+            // system does not have a way to express this yet.
+            let code = unsafe { NonZeroU32::new_unchecked(code) };
+            return Err(Error::from(code));
         }
     }
     Ok(())