wasmtime/runtime/vm/mpk/
sys.rs

1//! Expose the `pkey_*` Linux system calls. See the kernel documentation for
2//! more information:
3//! - [`pkeys`] overview
4//! - [`pkey_alloc`] (with `pkey_free`)
5//! - [`pkey_mprotect`]
6//! - `pkey_set` is implemented directly in assembly.
7//!
8//! [`pkey_alloc`]: https://man7.org/linux/man-pages/man2/pkey_alloc.2.html
9//! [`pkey_mprotect`]: https://man7.org/linux/man-pages/man2/pkey_mprotect.2.html
10//! [`pkeys`]: https://man7.org/linux/man-pages/man7/pkeys.7.html
11
12use crate::prelude::*;
13use crate::runtime::vm::host_page_size;
14use std::io::Error;
15
16/// Protection mask disallowing reads and writes of pkey-protected memory (see
17/// `prot` in [`pkey_mprotect`]); in Wasmtime we expect all MPK-protected memory
18/// to start as `PROT_NONE`.
19pub const PROT_NONE: u32 = libc::PROT_NONE as u32; // == 0b0000;
20
21/// Allocate a new protection key in the Linux kernel ([docs]); returns the
22/// key ID.
23///
24/// [docs]: https://man7.org/linux/man-pages/man2/pkey_alloc.2.html
25///
26/// Each process has its own separate pkey index; e.g., if process `m`
27/// allocates key 1, process `n` can as well.
28pub fn pkey_alloc(flags: u32, access_rights: u32) -> Result<u32> {
29    assert_eq!(flags, 0); // reserved for future use--must be 0.
30    let result = unsafe { libc::syscall(libc::SYS_pkey_alloc, flags, access_rights) };
31    if result >= 0 {
32        Ok(result
33            .try_into()
34            .expect("only pkey IDs between 0 and 15 are expected"))
35    } else {
36        debug_assert_eq!(result, -1); // only this error result is expected.
37        Err(Error::last_os_error().into())
38    }
39}
40
41/// Free a kernel protection key ([docs]).
42///
43/// [docs]: https://man7.org/linux/man-pages/man2/pkey_alloc.2.html
44#[allow(dead_code)]
45pub fn pkey_free(key: u32) -> Result<()> {
46    let result = unsafe { libc::syscall(libc::SYS_pkey_free, key) };
47    if result == 0 {
48        Ok(())
49    } else {
50        debug_assert_eq!(result, -1); // only this error result is expected.
51        Err(Error::last_os_error().into())
52    }
53}
54
55/// Change the access protections for a page-aligned memory region ([docs]).
56///
57/// [docs]: https://man7.org/linux/man-pages/man2/pkey_mprotect.2.html
58pub fn pkey_mprotect(addr: usize, len: usize, prot: u32, key: u32) -> Result<()> {
59    let page_size = host_page_size();
60    if addr % page_size != 0 {
61        log::warn!(
62            "memory must be page-aligned for MPK (addr = {addr:#x}, page size = {page_size}"
63        );
64    }
65    let result = unsafe { libc::syscall(libc::SYS_pkey_mprotect, addr, len, prot, key) };
66    if result == 0 {
67        Ok(())
68    } else {
69        debug_assert_eq!(result, -1); // only this error result is expected.
70        Err(Error::last_os_error().into())
71    }
72}
73
74#[cfg(test)]
75mod tests {
76    use super::*;
77
78    #[ignore = "cannot be run when keys() has already allocated all keys"]
79    #[test]
80    fn check_allocate_and_free() {
81        let key = pkey_alloc(0, 0).unwrap();
82        assert_eq!(key, 1);
83        // It may seem strange to assert the key ID here, but we already
84        // make some assumptions:
85        //  1. we are running on Linux with `pku` enabled
86        //  2. Linux will allocate key 0 for itself
87        //  3. we are running this test in non-MPK mode and no one else is
88        //     using pkeys
89        // If these assumptions are incorrect, this test can be removed.
90        pkey_free(key).unwrap()
91    }
92
93    #[test]
94    fn check_invalid_free() {
95        let result = pkey_free(42);
96        assert!(result.is_err());
97        assert_eq!(
98            result.unwrap_err().to_string(),
99            "Invalid argument (os error 22)"
100        );
101    }
102
103    #[test]
104    #[should_panic]
105    fn check_invalid_alloc_flags() {
106        let _ = pkey_alloc(42, 0);
107    }
108
109    #[test]
110    fn check_invalid_alloc_rights() {
111        assert!(pkey_alloc(0, 42).is_err());
112    }
113}
wasmtime/runtime/vm/mpk/sys.rs

wasmtime/runtime/vm/mpk/
sys.rs
