PR_SET_MDWE and PR_GET_MDWE

[rusty-snake]

Requesting support for PR_SET_MDWE and PR_GET_MDWE (Linux 6.3) as seen in the following PoC.

#![forbid(unsafe_op_in_unsafe_fn)]
#![allow(non_camel_case_types)]

use core::ffi::*;
use core::ptr;

type c_size_t = usize;
type c_off_t = i64;

const PR_SET_MDWE: i32 = 65;
//const PR_GET_MDWE: i32 = 66;

// Bitflags
const PR_MDWE_REFUSE_EXEC_GAIN: u64 = 1;

//const PROT_NONE: c_int = 0;
const PROT_READ: c_int = 1;
const PROT_WRITE: c_int = 2;
const PROT_EXEC: c_int = 4;

const MAP_PRIVATE: c_int = 0x0002;
const MAP_ANONYMOUS: c_int = 0x0020;

const MAP_FAILED: *mut c_void = -1 as _;

const EACCES: c_int = 13;

extern "C" {
    fn prctl(option: c_int, arg2: c_ulong, arg3: c_ulong, arg4: c_ulong, arg5: c_ulong) -> c_int;
    fn mmap(
        addr: *mut c_void,
        length: c_size_t,
        prot: c_int,
        flags: c_int,
        fd: c_int,
        offset: c_off_t,
    ) -> *mut c_void;
    fn mprotect(addr: *mut c_void, len: c_size_t, prot: c_int) -> c_int;
    fn __errno_location() -> *mut c_int;
}

fn prctl_set_mdwe(bits: u64) {
    let rv = unsafe { prctl(PR_SET_MDWE, bits, 0, 0, 0) };
    assert!(rv == 0);
}

fn main() {
    prctl_set_mdwe(PR_MDWE_REFUSE_EXEC_GAIN);

    let ptr1 = unsafe {
        mmap(
            ptr::null_mut(),
            4,
            PROT_WRITE | PROT_EXEC,
            MAP_PRIVATE | MAP_ANONYMOUS,
            -1,
            0,
        )
    };
    assert!(unsafe { *__errno_location() } == EACCES);
    assert!(ptr1 == MAP_FAILED);

    let ptr2 = unsafe {
        mmap(
            ptr::null_mut(),
            4,
            PROT_READ | PROT_WRITE,
            MAP_PRIVATE | MAP_ANONYMOUS,
            -1,
            0,
        )
    };
    let rv2 = unsafe { mprotect(ptr2, 4, PROT_EXEC) };
    assert!(unsafe { *__errno_location() } == EACCES);
    assert!(rv2 == -1);

    let ptr3 = unsafe {
        mmap(
            ptr::null_mut(),
            4,
            PROT_READ | PROT_EXEC,
            MAP_PRIVATE | MAP_ANONYMOUS,
            -1,
            0,
        )
    };
    let rv3 = unsafe { mprotect(ptr3, 4, PROT_EXEC) };
    assert!(rv3 == 0);
}

[rusty-snake]

btw, thanks. Choosing this crate was a good decision.