guard vdso overwrites with a static mutex

src/vdso.rs

@@ -5,6 +5,9 @@ use core::slice;
 use std::error::Error;
 use std::fs;
 use cacheflush_sys;
+use std::sync::Mutex;
+
+static vdso_mutex: Mutex<i32> = Mutex::new(0);
 
 #[derive(Debug, PartialEq)]
 pub(crate) struct DynSym {
@@ -107,6 +110,8 @@ impl vDSO {
     /// It is the caller's responsibility to provide the correct amount of data.
     pub(crate) fn overwrite(&self, symbol_address: usize, opcodes: &[u8]) {
         let dst_addr = self.avv.vdso_base + symbol_address;
+
+        let _guard = vdso_mutex.lock().unwrap();
         self.change_mode(true);
         unsafe {
             std::ptr::copy_nonoverlapping(opcodes.as_ptr(), dst_addr as *mut u8, opcodes.len())