AddrSan.cs

AddrSan.cs

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Intrinsics;

unsafe class Program
{
    [DllImport("kernel32")]
    static extern byte* VirtualAlloc(IntPtr addr, nuint size, uint typ, uint prot);

    static void Main()
    {
        // Case 1: pass 50 elements of a managed array
        int[] data = new int[50];
        Foo(ref data[0], 50);


        // Case 2: same amount of memory, just allocated at the page boundary
        uint length = (uint)Environment.SystemPageSize;
        byte* ptr = VirtualAlloc(IntPtr.Zero, length, 0x1000 | 0x2000 /* reserve commit */, 0x04);
        ref int pointer = ref Unsafe.AsRef<int>(ptr + length - 50 * sizeof(int));

        // pointer pointing to exactly 50 ints (200 bytes)
        Foo(ref pointer, 50);
    }

    static void Foo(ref int data, nuint length)
    {
        // This algorithm has a bug, it reads more than needed for last vector
        for (nuint i = 0; i < length; i += (nuint)Vector128<int>.Count)
        {
            Vector128<int> vec = Vector128.LoadUnsafe(ref data, i);
            vec += Vector128.Create(1);
            vec.StoreUnsafe(ref data, i);
        }
    }
}