fix: sys_rand() buf

Author: leruaa

library/std/src/sys/random/zkvm.rs

@@ -1,20 +1,20 @@
 use crate::sys::pal::abi;
 
 pub fn fill_bytes(bytes: &mut [u8]) {
-    let (pre, words, post) = unsafe { bytes.align_to_mut::<u32>() };
+    let (pre, words, post) = unsafe { bytes.align_to_mut::<u8>() };
     if !words.is_empty() {
         unsafe {
             abi::sys_rand(words.as_mut_ptr(), words.len());
         }
     }
 
-    let mut buf = [0u32; 2];
+    let mut buf = [0u8; 8];
     let len = (pre.len() + post.len() + size_of::<u32>() - 1) / size_of::<u32>();
     if len != 0 {
         unsafe { abi::sys_rand(buf.as_mut_ptr(), len) };
     }
 
-    let buf = buf.map(u32::to_ne_bytes);
+    let buf = buf.map(u8::to_ne_bytes);
     let buf = buf.as_flattened();
     pre.copy_from_slice(&buf[..pre.len()]);
     post.copy_from_slice(&buf[pre.len()..pre.len() + post.len()]);