System.AccessViolationException
The exception that is thrown when there is an attempt to read or write protected memory.
Minimum version: >= 2.0 >= Core 2.0
Statistics
24
How to handle it
try
{
}
catch (System.AccessViolationException e)
{
}try
{
}
catch (System.AccessViolationException e) when (e.Message.Contains("something"))
{
}try
{
}
catch (System.AccessViolationException e) when (LogException(e))
{
}
private static bool LogException(Exception e)
{
logger.LogError(...);
return false;
}How to avoid it
AccessViolationException is often thrown when trying to call some external C++ code or similar. There's no good way to avoid it in C# when calling external code, other than fixing the cause of the error in the target code. One thing to be aware of is that you will need to include the HandleProcessCorruptedStateExceptions attribute in your Main method to successfully catch this exception:
class Program
{
[HandleProcessCorruptedStateExceptions]
static void Main(string[] args)
{
try
{
ViolateMe();
}
catch (AccessViolationException e)
{
Console.WriteLine(e);
}
}
[DllImport(@"C:\path\to\ViolatorLib.dll")]
private static extern int ViolateMe();
}Links
YouTube videos
Possible fixes from StackOverflow
EDIT (3/17/2021)
Disclaimer: This answer was written in 2011 and references the original .NET Framework 4.0 implementation, NOT the open-source implementation of .NET.
In .NET 4.0, the runtime handles certain exceptions raised as Windows Structured Error Handling (SEH) errors as indicators of Corrupted State. These Corrupted State Exceptions (CSE) are not allowed to be caught by your standard managed code. I won't get into the why's or how's here. Read this article about CSE's in the .NET 4.0 Framework:
http://msdn.microsoft.com/en-us/magazine/dd419661.aspx#id0070035
But there is hope. There are a few ways to get around this:
Recompile as a .NET 3.5 assembly and run it in .NET 4.0.
Add a line to your application's config file under the configuration/runtime element:
<legacyCorruptedStateExceptionsPolicy enabled="true|false"/>Decorate the methods you want to catch these exceptions in with the
HandleProcessCorruptedStateExceptionsattribute. See http://msdn.microsoft.com/en-us/magazine/dd419661.aspx#id0070035 for details.
EDIT
Previously, I referenced a forum post for additional details. But since Microsoft Connect has been retired, here are the additional details in case you're interested:
From Gaurav Khanna, a developer from the Microsoft CLR Team
This behaviour is by design due to a feature of CLR 4.0 called Corrupted State Exceptions. Simply put, managed code shouldnt make an attempt to catch exceptions that indicate corrupted process state and AV is one of them.
He then goes on to reference the documentation on the HandleProcessCorruptedStateExceptionsAttribute and the above article. Suffice to say, it's definitely worth a read if you're considering catching these types of exceptions.
You cannot pass a C++ std::string across an interop boundary. You cannot create one of those in your C# code. So your code can never work.
You need to use interop friendly types at the interop boundary. For instance, null-terminated arrays of characters. That works well when you allocate and deallocate the memory in the same module. So, it's simple enough when passing data from C# to C++.
C++
void foo(const char *str)
{
// do something with str
}
C#
[DllImport("...", CallingConvention = CallingConvention.Cdecl)
static extern void foo(string str);
....
foo("bar");
In the other direction you would typically expect the caller to allocate the buffer, into which the callee can write:
C++
void foo(char *str, int len)
{
// write no more than len characters into str
}
C#
[DllImport("...", CallingConvention = CallingConvention.Cdecl)
static extern void foo(StringBuilder str, int len);
....
StringBuilder sb = new StringBuilder(10);
foo(sb, sb.Capacity);
I had the same problem after upgrading from .NET 4.5 to .NET 4.5.1. What fixed it for me was running this command:
netsh winsock reset
I'm fairly certain you're being blocked by DEP. The x_CPUIDy_INSNS byte arrays are in a segment of memory marked as data and non-executable.
EDIT:
That being said, I've gotten a version that compiles and runs, but I don't think gets the right values. Perhaps this will get you along your way.
EDIT 2:
I think I have the right values coming back now. Feel free to validate.
namespace CPUID
{
using System;
using System.Globalization;
using System.Linq;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Text;
internal static class Program
{
[Flags]
private enum AllocationTypes : uint
{
Commit = 0x1000,
Reserve = 0x2000,
Reset = 0x80000,
LargePages = 0x20000000,
Physical = 0x400000,
TopDown = 0x100000,
WriteWatch = 0x200000
}
[Flags]
private enum MemoryProtections : uint
{
Execute = 0x10,
ExecuteRead = 0x20,
ExecuteReadWrite = 0x40,
ExecuteWriteCopy = 0x80,
NoAccess = 0x01,
ReadOnly = 0x02,
ReadWrite = 0x04,
WriteCopy = 0x08,
GuartModifierflag = 0x100,
NoCacheModifierflag = 0x200,
WriteCombineModifierflag = 0x400
}
[Flags]
private enum FreeTypes : uint
{
Decommit = 0x4000,
Release = 0x8000
}
[UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]
private unsafe delegate void CPUID0Delegate(byte* buffer);
[UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]
private unsafe delegate void CPUID1Delegate(byte* buffer);
private static void Main()
{
Console.WriteLine("CPUID0: {0}", string.Join(", ", CPUID0().Select(x => x.ToString("X2", CultureInfo.InvariantCulture))));
Console.WriteLine("CPUID0: {0}", new string(ASCIIEncoding.ASCII.GetChars(CPUID0())));
Console.WriteLine("CPUID1: {0}", string.Join(", ", CPUID1().Select(x => x.ToString("X2", CultureInfo.InvariantCulture))));
Console.ReadLine();
}
private static unsafe byte[] CPUID0()
{
byte[] buffer = new byte[12];
if (IntPtr.Size == 4)
{
IntPtr p = NativeMethods.VirtualAlloc(
IntPtr.Zero,
new UIntPtr((uint)x86_CPUID0_INSNS.Length),
AllocationTypes.Commit | AllocationTypes.Reserve,
MemoryProtections.ExecuteReadWrite);
try
{
Marshal.Copy(x86_CPUID0_INSNS, 0, p, x86_CPUID0_INSNS.Length);
CPUID0Delegate del = (CPUID0Delegate)Marshal.GetDelegateForFunctionPointer(p, typeof(CPUID0Delegate));
fixed (byte* newBuffer = &buffer[0])
{
del(newBuffer);
}
}
finally
{
NativeMethods.VirtualFree(p, 0, FreeTypes.Release);
}
}
else if (IntPtr.Size == 8)
{
IntPtr p = NativeMethods.VirtualAlloc(
IntPtr.Zero,
new UIntPtr((uint)x64_CPUID0_INSNS.Length),
AllocationTypes.Commit | AllocationTypes.Reserve,
MemoryProtections.ExecuteReadWrite);
try
{
Marshal.Copy(x64_CPUID0_INSNS, 0, p, x64_CPUID0_INSNS.Length);
CPUID0Delegate del = (CPUID0Delegate)Marshal.GetDelegateForFunctionPointer(p, typeof(CPUID0Delegate));
fixed (byte* newBuffer = &buffer[0])
{
del(newBuffer);
}
}
finally
{
NativeMethods.VirtualFree(p, 0, FreeTypes.Release);
}
}
return buffer;
}
private static unsafe byte[] CPUID1()
{
byte[] buffer = new byte[12];
if (IntPtr.Size == 4)
{
IntPtr p = NativeMethods.VirtualAlloc(
IntPtr.Zero,
new UIntPtr((uint)x86_CPUID1_INSNS.Length),
AllocationTypes.Commit | AllocationTypes.Reserve,
MemoryProtections.ExecuteReadWrite);
try
{
Marshal.Copy(x86_CPUID1_INSNS, 0, p, x86_CPUID1_INSNS.Length);
CPUID1Delegate del = (CPUID1Delegate)Marshal.GetDelegateForFunctionPointer(p, typeof(CPUID1Delegate));
fixed (byte* newBuffer = &buffer[0])
{
del(newBuffer);
}
}
finally
{
NativeMethods.VirtualFree(p, 0, FreeTypes.Release);
}
}
else if (IntPtr.Size == 8)
{
IntPtr p = NativeMethods.VirtualAlloc(
IntPtr.Zero,
new UIntPtr((uint)x64_CPUID1_INSNS.Length),
AllocationTypes.Commit | AllocationTypes.Reserve,
MemoryProtections.ExecuteReadWrite);
try
{
Marshal.Copy(x64_CPUID1_INSNS, 0, p, x64_CPUID1_INSNS.Length);
CPUID1Delegate del = (CPUID1Delegate)Marshal.GetDelegateForFunctionPointer(p, typeof(CPUID1Delegate));
fixed (byte* newBuffer = &buffer[0])
{
del(newBuffer);
}
}
finally
{
NativeMethods.VirtualFree(p, 0, FreeTypes.Release);
}
}
return buffer;
}
private static class NativeMethods
{
[DllImport("kernel32.dll", SetLastError = true)]
internal static extern IntPtr VirtualAlloc(
IntPtr lpAddress,
UIntPtr dwSize,
AllocationTypes flAllocationType,
MemoryProtections flProtect);
[DllImport("kernel32")]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern bool VirtualFree(
IntPtr lpAddress,
uint dwSize,
FreeTypes flFreeType);
}
#region ASM
private static readonly byte[] x86_CPUID0_INSNS = new byte[]
{
0x53, // push %ebx
0x31, 0xc0, // xor %eax,%eax
0x0f, 0xa2, // cpuid
0x8b, 0x44, 0x24, 0x08, // mov 0x8(%esp),%eax
0x89, 0x18, // mov %ebx,0x0(%eax)
0x89, 0x50, 0x04, // mov %edx,0x4(%eax)
0x89, 0x48, 0x08, // mov %ecx,0x8(%eax)
0x5b, // pop %ebx
0xc3 // ret
};
private static readonly byte[] x86_CPUID1_INSNS = new byte[]
{
0x53, // push %ebx
0x31, 0xc0, // xor %eax,%eax
0x40, // inc %eax
0x0f, 0xa2, // cpuid
0x5b, // pop %ebx
0xc3 // ret
};
private static readonly byte[] x64_CPUID0_INSNS = new byte[]
{
0x49, 0x89, 0xd8, // mov %rbx,%r8
0x49, 0x89, 0xc9, // mov %rcx,%r9
0x48, 0x31, 0xc0, // xor %rax,%rax
0x0f, 0xa2, // cpuid
0x4c, 0x89, 0xc8, // mov %r9,%rax
0x89, 0x18, // mov %ebx,0x0(%rax)
0x89, 0x50, 0x04, // mov %edx,0x4(%rax)
0x89, 0x48, 0x08, // mov %ecx,0x8(%rax)
0x4c, 0x89, 0xc3, // mov %r8,%rbx
0xc3 // retq
};
private static readonly byte[] x64_CPUID1_INSNS = new byte[]
{
0x53, // push %rbx
0x48, 0x31, 0xc0, // xor %rax,%rax
0x48, 0xff, 0xc0, // inc %rax
0x0f, 0xa2, // cpuid
0x5b, // pop %rbx
0xc3 // retq
};
#endregion
}
}
I decided to improve your answer. It does not need unsafe to compile anymore, and it only needs two assembly blocks in order to be able to read out any and all cpuid blocks, because it just writes eax/ebx/ecx/edx to a 16-byte byte array.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using System.Runtime.InteropServices;
namespace CpuID
{
public class CpuID : IDisposable
{
[UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]
public delegate void CpuIDDelegate(int level, byte[] buffer);
[DllImport("kernel32.dll", SetLastError = true)]
private static extern IntPtr VirtualAlloc(
IntPtr lpAddress,
UIntPtr dwSize,
AllocationType flAllocationType,
MemoryProtection flProtect
);
[DllImport("kernel32")]
private static extern bool VirtualFree(
IntPtr lpAddress,
UInt32 dwSize,
UInt32 dwFreeType
);
[Flags()]
public enum AllocationType : uint
{
COMMIT = 0x1000,
RESERVE = 0x2000,
RESET = 0x80000,
LARGE_PAGES = 0x20000000,
PHYSICAL = 0x400000,
TOP_DOWN = 0x100000,
WRITE_WATCH = 0x200000
}
[Flags()]
public enum MemoryProtection : uint
{
EXECUTE = 0x10,
EXECUTE_READ = 0x20,
EXECUTE_READWRITE = 0x40,
EXECUTE_WRITECOPY = 0x80,
NOACCESS = 0x01,
READONLY = 0x02,
READWRITE = 0x04,
WRITECOPY = 0x08,
GUARD_Modifierflag = 0x100,
NOCACHE_Modifierflag = 0x200,
WRITECOMBINE_Modifierflag = 0x400
}
private CpuIDDelegate cpuIdDelg;
private IntPtr codePointer;
// void x86CpuId(int level, byte* buffer)
// {
// eax = level
// cpuid
// buffer[0] = eax
// buffer[4] = ebx
// buffer[8] = ecx
// buffer[12] = edx
// }
private byte[] x86CodeBytes =
{
0x55, // push ebp
0x8B, 0xEC, // mov ebp,esp
0x53, // push ebx
0x57, // push edi
0x8B, 0x45, 0x08, // mov eax, dword ptr [ebp+8] (move level into eax)
0x0F, 0xA2, // cpuid
0x8B, 0x7D, 0x0C, // mov edi, dword ptr [ebp+12] (move address of buffer into edi)
0x89, 0x07, // mov dword ptr [edi+0], eax (write eax, ... to buffer)
0x89, 0x5F, 0x04, // mov dword ptr [edi+4], ebx
0x89, 0x4F, 0x08, // mov dword ptr [edi+8], ecx
0x89, 0x57, 0x0C, // mov dword ptr [edi+12],edx
0x5F, // pop edi
0x5B, // pop ebx
0x8B, 0xE5, // mov esp,ebp
0x5D, // pop ebp
0xc3 // ret
};
private byte[] x64CodeBytes =
{
0x53, // push rbx this gets clobbered by cpuid
// rcx is level
// rdx is buffer.
// Need to save buffer elsewhere, cpuid overwrites rdx
// Put buffer in r8, use r8 to reference buffer later.
// Save rdx (buffer addy) to r8
0x49, 0x89, 0xd0, // mov r8, rdx
// Move ecx (level) to eax to call cpuid, call cpuid
0x89, 0xc8, // mov eax, ecx
0x0F, 0xA2, // cpuid
// Write eax et al to buffer
0x41, 0x89, 0x40, 0x00, // mov dword ptr [r8+0], eax
0x41, 0x89, 0x58, 0x04, // mov dword ptr [r8+4], ebx
0x41, 0x89, 0x48, 0x08, // mov dword ptr [r8+8], ecx
0x41, 0x89, 0x50, 0x0c, // mov dword ptr [r8+12], edx
0x5b, // pop rbx
0xc3 // ret
};
public CpuID()
{
Compile();
}
~CpuID()
{
Dispose(false);
}
private void Compile()
{
byte[] codeBytes;
if (IntPtr.Size == 4)
{
codeBytes = x86CodeBytes;
}
else
{
codeBytes = x64CodeBytes;
}
this.codePointer = VirtualAlloc(
IntPtr.Zero,
new UIntPtr((uint)codeBytes.Length),
AllocationType.COMMIT | AllocationType.RESERVE,
MemoryProtection.EXECUTE_READWRITE
);
Marshal.Copy(codeBytes, 0, this.codePointer, codeBytes.Length);
this.cpuIdDelg = (CpuIDDelegate)Marshal.GetDelegateForFunctionPointer(this.codePointer, typeof(CpuIDDelegate));
}
public void Invoke(int level, byte[] buffer)
{
GCHandle handle = default(GCHandle);
if (buffer.Length < 16)
{
throw new ArgumentException("buffer must be at least 16 bytes long");
}
try
{
handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
this.cpuIdDelg(level, buffer);
}
finally
{
if (handle != default(GCHandle))
{
handle.Free();
}
}
}
public void Dispose()
{
Dispose(true);
}
public void Dispose(bool disposing)
{
if (this.codePointer != IntPtr.Zero)
{
VirtualFree(this.codePointer, 0, 0x8000);
this.codePointer = IntPtr.Zero;
}
}
}
}
Source: Stack Overflow