minimal_rt/
enlightened_panic.rs

1// Copyright (c) Microsoft Corporation.
2// Licensed under the MIT License.
3
4//! Enlightened panic for a Hyper-V guest.
5
6//! Hyper-V guests may choose to report a crash to the Hyper-V host
7//! via a set of MSRs (x64) or synthetic crash registers on ARM.
8//! The registers carry crash-specific information and may optionally
9//! include a message buffer.
10
11use crate::arch::write_crash_reg;
12use arrayvec::ArrayString;
13use core::fmt::Write;
14use core::sync::atomic::AtomicBool;
15use core::sync::atomic::Ordering::Relaxed;
16use hvdef::GuestCrashCtl;
17
18// This is chosen to identify the boot shim as a pre-OS environment
19const PRE_OS_ID: u8 = 5;
20
21static CAN_REPORT_MSG: AtomicBool = AtomicBool::new(false);
22
23fn report_raw(tag: [u8; 8], msg: &[u8], msg_pa: Option<usize>) {
24    // Before using the guest crash MSRs, could check
25    // if these are supported. Here, we don't do that
26    // as the intention is to fault anyways.
27
28    let crash_ctl = GuestCrashCtl::new()
29        .with_pre_os_id(PRE_OS_ID)
30        .with_no_crash_dump(true)
31        .with_crash_message(!msg.is_empty())
32        .with_crash_notify(true);
33
34    // SAFETY: Using the contract established in the Hyper-V TLFS.
35    unsafe {
36        write_crash_reg(0, u64::from_le_bytes(*b"BOOTSHIM"));
37        write_crash_reg(1, u64::from_be_bytes(tag));
38        write_crash_reg(2, u64::MAX);
39
40        match (msg, msg_pa) {
41            (msg @ [_, ..], Some(msg_pa)) => {
42                // There is a non-empty message and a valid physical address.
43                write_crash_reg(3, msg_pa as u64);
44                write_crash_reg(4, msg.len() as u64);
45            }
46            _ => {
47                write_crash_reg(3, 0);
48                write_crash_reg(4, 0);
49            }
50        }
51
52        // Report crash to Hyper-V
53        write_crash_reg(5, crash_ctl.into());
54    }
55}
56
57/// Reports the panic.
58///
59/// `stack_va_to_pa` takes an object on the stack and returns its physical address.
60pub fn report(
61    tag: [u8; 8],
62    panic: &core::panic::PanicInfo<'_>,
63    mut stack_va_to_pa: impl FnMut(*const ()) -> Option<usize>,
64) {
65    let mut panic_buffer = ArrayString::<512>::new();
66    if CAN_REPORT_MSG.load(Relaxed) {
67        let _ = write!(panic_buffer, "{}", panic);
68    }
69    report_raw(
70        tag,
71        panic_buffer.as_bytes(),
72        stack_va_to_pa(panic_buffer.as_bytes().as_ptr().cast()),
73    );
74}
75
76/// Enables writing the enlightened panic message.
77///
78/// If this is not called, then [`report`] will just report that a panic occurred
79/// and not include the panic message.
80pub fn enable_enlightened_panic() {
81    CAN_REPORT_MSG.store(true, Relaxed);
82}
minimal_rt/enlightened_panic.rs

minimal_rt/
enlightened_panic.rs
