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• Rust Win32 FFI : User-mode data execution prevention (DEP) violation

  28 avril 2022, par TheElix

  I'm trying to pass a ID3D11Device instance from Rust to a C FFI Library (FFMPEG).

  


  I made this sample code :

  


  pub fn create_d3d11_device(&amp;mut self, device: &amp;mut Box, context: &amp;mut Box) {&#xA;            let av_device : Box<avbufferref> = self.alloc(HwDeviceType::D3d11va);&#xA;            unsafe {&#xA;                let device_context = Box::from_raw(av_device.data as *mut AVHWDeviceContext);&#xA;                let mut d3d11_device_context = Box::from_raw(device_context.hwctx as *mut AVD3D11VADeviceContext);&#xA;                d3d11_device_context.device = device.as_mut() as *mut _;&#xA;                d3d11_device_context.device_context = context.as_mut() as *mut _;&#xA;                let avp = Box::into_raw(av_device);&#xA;                av_hwdevice_ctx_init(avp);&#xA;                self.av_hwdevice = Some(Box::from_raw(avp));&#xA;            }&#xA;        }&#xA;</avbufferref>

  


  On the Rust side the Device does work, but on the C side, when FFMEPG calls ID3D11DeviceContext_QueryInterface the app crashes with the following error : Exception 0xc0000005 encountered at address 0x7ff9fb99ad38: User-mode data execution prevention (DEP) violation at location 0x7ff9fb99ad38

  


  The address is actually the pointer for the lpVtbl of QueryInterface, like seen here :

  


  The disassembly of the address also looks correct (this is done on an another debugging session) :

  


  (lldb) disassemble --start-address 0x00007ffffdf3ad38
    0x7ffffdf3ad38: addb   %ah, 0x7ffffd(%rdi,%riz,8)
    0x7ffffdf3ad3f: addb   %al, (%rax)
    0x7ffffdf3ad41: movabsl -0x591fffff80000219, %eax
    0x7ffffdf3ad4a: outl   %eax, $0xfd


  


  Do you have any pointer to debug this further ?

  


  EDIT : I made a Minimal Reproducion Sample. Interestingly this does not causes a DEP Violation, but simply a Segfault.

  


  On the C side :

  


  int test_ffi(ID3D11Device *device){
    ID3D11DeviceContext *context;
    device->lpVtbl->GetImmediateContext(device, &context);
    if (!context) return 1;
    return 0;
}


  


  On the Rust side :

  


  unsafe fn main_rust(){
    let mut device = None;
    let mut device_context = None;
    let _ = match windows::Win32::Graphics::Direct3D11::D3D11CreateDevice(None, D3D_DRIVER_TYPE_HARDWARE, OtherHinstance::default(), D3D11_CREATE_DEVICE_DEBUG, &[], D3D11_SDK_VERSION, &mut device, std::ptr::null_mut(), &mut device_context) {
        Ok(e) => e,
        Err(e) => panic!("Creation Failed: {}", e)
    };
    let mut device = match device {
        Some(e) => e,
        None => panic!("Creation Failed2")
    };
    let mut f2 : ID3D11Device = transmute_copy(&device); //Transmuting the WinAPI into a bindgen ID3D11Device
    test_ffi(&mut f2);
}


  


  The bindgen build.rs :

  


  extern crate bindgen;

use std::env;
use std::path::PathBuf;

fn main() {
    // Tell cargo to tell rustc to link the system bzip2
    // shared library.
    println!("cargo:rustc-link-lib=ffi_demoLIB");
    println!("cargo:rustc-link-lib=d3d11");

    // Tell cargo to invalidate the built crate whenever the wrapper changes
    println!("cargo:rerun-if-changed=library.h");

    // The bindgen::Builder is the main entry point
    // to bindgen, and lets you build up options for
    // the resulting bindings.
    let bindings = bindgen::Builder::default()
        // The input header we would like to generate
        // bindings for.
        .header("library.h")
        // Tell cargo to invalidate the built crate whenever any of the
        // included header files changed.
        .parse_callbacks(Box::new(bindgen::CargoCallbacks))
        .blacklist_type("_IMAGE_TLS_DIRECTORY64")
        .blacklist_type("IMAGE_TLS_DIRECTORY64")
        .blacklist_type("PIMAGE_TLS_DIRECTORY64")
        .blacklist_type("IMAGE_TLS_DIRECTORY")
        .blacklist_type("PIMAGE_TLS_DIRECTORY")
        // Finish the builder and generate the bindings.
        .generate()
        // Unwrap the Result and panic on failure.
        .expect("Unable to generate bindings");

    // Write the bindings to the $OUT_DIR/bindings.rs file.
    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
    bindings
        .write_to_file(out_path.join("bindings.rs"))
        .expect("Couldn't write bindings!");
}


  


  The Complete Repo can be found over here : https://github.com/TheElixZammuto/demo-ffi

  


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