Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

8 files changed, 662 insertions, 0 deletions

diff --git a/toolkit/xre/detect_win32k_conflicts/.gitignore b/toolkit/xre/detect_win32k_conflicts/.gitignore
new file mode 100644
index 0000000000..869df07dae
--- /dev/null
+++ b/toolkit/xre/detect_win32k_conflicts/.gitignore
@@ -0,0 +1,2 @@
+/target
+Cargo.lock
\ No newline at end of file
diff --git a/toolkit/xre/detect_win32k_conflicts/Cargo.toml b/toolkit/xre/detect_win32k_conflicts/Cargo.toml
new file mode 100644
index 0000000000..a94402df9e
--- /dev/null
+++ b/toolkit/xre/detect_win32k_conflicts/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "detect_win32k_conflicts"
+version = "0.1.0"
+edition = "2021"
+license = "MPL-2.0"
+
+[dependencies]
+log = "0.4"
+thiserror = "1"
+winapi = { version = "0.3", features = ["winerror", "winreg"] }
diff --git a/toolkit/xre/detect_win32k_conflicts/src/detect.rs b/toolkit/xre/detect_win32k_conflicts/src/detect.rs
new file mode 100644
index 0000000000..e21c80e157
--- /dev/null
+++ b/toolkit/xre/detect_win32k_conflicts/src/detect.rs
@@ -0,0 +1,165 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! This module contains the actual functions that explore the registry for the status
+//! of the conflicting mitigations.
+
+use super::error::DetectConflictError;
+use super::registry::{RegKey, RegValue};
+
+use std::ffi::OsStr;
+
+/// Subkey that the Windows Exploit Protection status is located in
+const EXPLOIT_PROTECTION_SUBKEY: &str =
+    "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Image File Execution Options";
+
+/// Name of the value within that subkey that contains the exploit protection status
+const MITIGATION_VALUE_NAME: &str = "MitigationOptions";
+
+/// The bit number within the value with the StackPivot status
+const STACK_PIVOT_BIT: usize = 80;
+
+/// The bit number within the value with the CallerCheck status
+const CALLER_CHECK_BIT: usize = 84;
+
+/// The bit number within the value with the SimExec status
+const SIM_EXEC_BIT: usize = 88;
+
+/// Printable, FFI-safe structure containing the status of the conflicting mitigations
+#[repr(C)]
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct ConflictingMitigationStatus {
+    /// The status of the CallerCheck feature. 0 = disabled, 1 = enabled
+    caller_check: bool,
+    /// The status of the SimExec feature. 0 = disabled, 1 = enabled
+    sim_exec: bool,
+    /// The status of the StackPivot feature. 0 = disabled, 1 = enabled
+    stack_pivot: bool,
+}
+
+impl std::fmt::Display for ConflictingMitigationStatus {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+        use std::fmt::Write;
+        write_status(f, "CallerCheck", self.caller_check)?;
+        f.write_char(' ')?;
+        write_status(f, "SimExec", self.sim_exec)?;
+        f.write_char(' ')?;
+        write_status(f, "StackPivot", self.stack_pivot)
+    }
+}
+
+/// Search the registry for win32k-conflicting mitigations for the given process
+///
+/// `process_name` is the name of the process that will be checked for conflicting mitigations
+/// It uses the same case-insensitive algorithm that the Windows Registry uses itself to detect
+/// whether a process needs mitigations or not
+///
+/// (This will usually be `firefox.exe`)
+///
+/// # Caveat
+///
+/// Windows allows an arbitrary number of "filters", which are subkeys of the main key
+/// that also have a `MitigationOptions` value. They are used to allow filtering by path.
+///
+/// For simplicity, we "flatten" the path filters when we figure this out, and so the
+/// returned value will be the logical "OR" of all mitigations enabled with any filter
+///
+/// So if there are two entries for "C:\Firefox\firefox.exe" with mitigations `A` and `B` enabled
+/// and another entry for "C:\Program Files\Mozilla Firefox\firefox.exe" with mitigation `C`
+/// enabled, we will return that `A`, `B`, and `C` are all enabled
+pub fn get_conflicting_mitigations(
+    process_name: impl AsRef<OsStr>,
+) -> Result<ConflictingMitigationStatus, DetectConflictError> {
+    let process_name = process_name.as_ref();
+
+    let key = RegKey::root_local_machine()
+        .try_open_subkey(EXPLOIT_PROTECTION_SUBKEY)?
+        .ok_or(DetectConflictError::ExploitProtectionKeyMissing)?;
+
+    let process_key = match key.try_open_subkey(process_name)? {
+        Some(key) => key,
+        None => {
+            log::info!(
+                "process name {:?} not found in exploit protection",
+                process_name
+            );
+            return Ok(ConflictingMitigationStatus::default());
+        }
+    };
+
+    // First get mitigation status for the root key
+    let mut status = get_conflicting_mitigations_for_key(&process_key)?;
+
+    // Then get mitigation status for each subkey and logical-or them all together
+    for subkey_name in process_key.subkey_names() {
+        let subkey_name = subkey_name?;
+
+        let subkey = process_key
+            .try_open_subkey(subkey_name)?
+            .expect("a subkey somehow doesn't exist after enumerating it");
+
+        let subkey_status = get_conflicting_mitigations_for_key(&subkey)?;
+        status.caller_check |= subkey_status.caller_check;
+        status.sim_exec |= subkey_status.sim_exec;
+        status.stack_pivot |= subkey_status.stack_pivot;
+    }
+
+    log::info!(
+        "process name {:?} has mitigation status {:?}",
+        process_name,
+        status
+    );
+
+    Ok(status)
+}
+
+/// Check a key to see if it has a "MitigationOptions" value with any conflicting mitigations
+/// enabled
+fn get_conflicting_mitigations_for_key(
+    key: &RegKey,
+) -> Result<ConflictingMitigationStatus, DetectConflictError> {
+    let value = match key.try_get_value(MITIGATION_VALUE_NAME)? {
+        Some(value) => value,
+        None => return Ok(ConflictingMitigationStatus::default()),
+    };
+
+    let bits = match value {
+        RegValue::Binary(bits) => bits,
+        _ => return Ok(ConflictingMitigationStatus::default()),
+    };
+
+    Ok(ConflictingMitigationStatus {
+        caller_check: get_bit(&bits, CALLER_CHECK_BIT)?,
+        sim_exec: get_bit(&bits, SIM_EXEC_BIT)?,
+        stack_pivot: get_bit(&bits, STACK_PIVOT_BIT)?,
+    })
+}
+
+/// Retrieve a bit from a vector-of-bitflags, which is what will be returned by the registry
+/// entry for exploit protection. The bits are numbered first by increasing value within a byte,
+/// and then by increasing index within the slice.
+///
+/// Ex: bit 0 = (index 0, mask 0x01), bit 7 = (index 0, mask 0x80), bit 8 = (index 1, mask 0x01)
+fn get_bit(bytes: &[u8], bit_idx: usize) -> Result<bool, DetectConflictError> {
+    let byte = bytes
+        .get(bit_idx / 8)
+        .ok_or(DetectConflictError::RegValueTooShort)?;
+
+    Ok(if byte & (1 << (bit_idx % 8)) != 0 {
+        true
+    } else {
+        false
+    })
+}
+
+/// Write the status of a feature to the given formatter. `bit == 0` means feature is disabled,
+/// `bit == 1` means enabled
+fn write_status(
+    f: &mut std::fmt::Formatter<'_>,
+    name: &str,
+    bit: bool,
+) -> Result<(), std::fmt::Error> {
+    let status_str = if bit { "enabled" } else { "disabled" };
+    write!(f, "{} is {}.", name, status_str)
+}
diff --git a/toolkit/xre/detect_win32k_conflicts/src/error.rs b/toolkit/xre/detect_win32k_conflicts/src/error.rs
new file mode 100644
index 0000000000..cc73d04b2d
--- /dev/null
+++ b/toolkit/xre/detect_win32k_conflicts/src/error.rs
@@ -0,0 +1,36 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Contains the error type for this crate
+
+use thiserror::Error;
+
+/// The error type for this crate
+#[derive(Debug, Error)]
+pub enum DetectConflictError {
+    /// An exploit protection key was not found in the registry
+    #[error("exploit protection key missing")]
+    ExploitProtectionKeyMissing,
+    /// Failed to enumerate the next registry subkey
+    #[error("failed to enumerate next registry subkey. code: {0}")]
+    RegEnumKeyFailed(u32),
+    /// Failed to get a value from the registry
+    #[error("failed to get registry value. code: {0}")]
+    RegGetValueFailed(u32),
+    /// Failed to get the length of a value from the registry
+    #[error("failed to get registry value length. code: {0}")]
+    RegGetValueLenFailed(u32),
+    /// Failed to open a registry key
+    #[error("failed to open registry key. code: {0}")]
+    RegOpenKeyFailed(u32),
+    /// Exploit Protection registry value was too short
+    #[error("exploit protection registry value too short")]
+    RegValueTooShort,
+    /// Failed to query key for subkey length
+    #[error("failed to query key for max subkey length. code: {0}")]
+    RegQueryInfoKeyFailed(u32),
+    /// A registry value had an unsupported type
+    #[error("key has unsupported value type: {0}")]
+    UnsupportedValueType(u32),
+}
diff --git a/toolkit/xre/detect_win32k_conflicts/src/ffi.rs b/toolkit/xre/detect_win32k_conflicts/src/ffi.rs
new file mode 100644
index 0000000000..826f452726
--- /dev/null
+++ b/toolkit/xre/detect_win32k_conflicts/src/ffi.rs
@@ -0,0 +1,57 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! C foreign-function interface for this crate
+
+use super::detect::{get_conflicting_mitigations, ConflictingMitigationStatus};
+
+/// C FFI for `get_conflicting_mitigations`
+///
+/// Checks the current process to see if any conflicting mitigations would be enabled
+/// by Windows Exploit Protection
+///
+/// `conflicting_mitigations` is an out pointer that will receive the status of the
+/// Win32k conflicting mitigations
+///
+/// On success, returns `1`. On failure, returns `0` and `conflicting_mitigations` is left
+/// untouched
+///
+/// # Safety
+///
+/// `conflicting_mitigations` must not be a non-const, non-null ptr and **must be initialized**
+///
+/// # Example
+///
+/// ```C++
+/// void myFunc() {
+///     ConflictingMitigationStatus status = {}; // GOOD - value-initializes the object
+///     if(!detect_win32k_conflicting_mitigations(&status)) {
+///         // error
+///     }
+/// }
+/// ```
+#[no_mangle]
+pub unsafe extern "C" fn detect_win32k_conflicting_mitigations(
+    conflicting_mitigations: &mut ConflictingMitigationStatus,
+) -> bool {
+    let process_path =
+        std::env::current_exe().expect("unable to determine the path of our executable");
+    let file_name = process_path
+        .file_name()
+        .expect("executable doesn't have a file name");
+
+    match get_conflicting_mitigations(file_name) {
+        Ok(status) => {
+            *conflicting_mitigations = status;
+            true
+        }
+        Err(e) => {
+            log::error!(
+                "Failed to get Win32k Lockdown conflicting mitigation status: {}",
+                e
+            );
+            false
+        }
+    }
+}
diff --git a/toolkit/xre/detect_win32k_conflicts/src/lib.rs b/toolkit/xre/detect_win32k_conflicts/src/lib.rs
new file mode 100644
index 0000000000..4333603b92
--- /dev/null
+++ b/toolkit/xre/detect_win32k_conflicts/src/lib.rs
@@ -0,0 +1,18 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Crate to detect Windows Exploit Protection mitigations that may interfere with Win32k
+//! Lockdown
+
+#![deny(missing_docs)]
+
+mod detect;
+mod error;
+mod ffi;
+mod registry;
+
+pub use self::detect::get_conflicting_mitigations;
+pub use self::detect::ConflictingMitigationStatus;
+pub use self::error::DetectConflictError;
+pub use self::ffi::detect_win32k_conflicting_mitigations;
diff --git a/toolkit/xre/detect_win32k_conflicts/src/registry.rs b/toolkit/xre/detect_win32k_conflicts/src/registry.rs
new file mode 100644
index 0000000000..f375a64284
--- /dev/null
+++ b/toolkit/xre/detect_win32k_conflicts/src/registry.rs
@@ -0,0 +1,360 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! This module contains helpers for exploring the Windows Registry
+
+use super::error::DetectConflictError;
+
+use std::ffi::{OsStr, OsString};
+use std::os::windows::ffi::{OsStrExt, OsStringExt};
+
+use winapi::{
+    shared::{
+        minwindef::HKEY,
+        winerror::{ERROR_FILE_NOT_FOUND, ERROR_NO_MORE_ITEMS, ERROR_SUCCESS},
+    },
+    um::{
+        winnt::{KEY_READ, REG_BINARY, REG_DWORD, REG_SZ},
+        winreg::{
+            RegCloseKey, RegEnumKeyExW, RegGetValueW, RegOpenKeyExW, RegQueryInfoKeyW,
+            HKEY_LOCAL_MACHINE, RRF_RT_REG_BINARY, RRF_RT_REG_DWORD, RRF_RT_REG_SZ,
+        },
+    },
+};
+
+/// An open key in the Windows Registry
+///
+/// (Note that Windows ref-counts keys internally, so we don't need subkeys to "hang on" to
+/// their parents)
+#[derive(Debug)]
+pub struct RegKey {
+    /// The Win32 handle of the open key
+    handle: HKEY,
+}
+
+impl RegKey {
+    /// Open the global HKEY_LOCAL_MACHINE handle
+    pub fn root_local_machine() -> RegKey {
+        RegKey {
+            handle: HKEY_LOCAL_MACHINE,
+        }
+    }
+    /// Try to open a subkey relative to this key with read-only access rights
+    ///
+    /// Returns `None` if the subkey doesn't exist
+    pub fn try_open_subkey(
+        &self,
+        subkey: impl AsRef<OsStr>,
+    ) -> Result<Option<RegKey>, DetectConflictError> {
+        let win32_subkey = to_win32_string(subkey.as_ref());
+
+        let mut subkey_handle = std::ptr::null_mut();
+        let rv = unsafe {
+            RegOpenKeyExW(
+                self.handle,
+                win32_subkey.as_ptr(),
+                0, // options
+                KEY_READ,
+                &mut subkey_handle,
+            )
+        }
+        .try_into()
+        .unwrap();
+
+        match rv {
+            ERROR_SUCCESS => {
+                assert!(!subkey_handle.is_null());
+
+                Ok(Some(RegKey {
+                    handle: subkey_handle,
+                }))
+            }
+            ERROR_FILE_NOT_FOUND => Ok(None),
+            _ => Err(DetectConflictError::RegOpenKeyFailed(rv)),
+        }
+    }
+    /// Try to get a value with the given name
+    ///
+    /// Returns `None` if there is no value with that name
+    ///
+    /// Note that you can pass the empty string to get the default value
+    pub fn try_get_value(
+        &self,
+        value_name: impl AsRef<OsStr>,
+    ) -> Result<Option<RegValue>, DetectConflictError> {
+        let win32_value_name = to_win32_string(value_name.as_ref());
+
+        // First we query the value's length and type so we know how to create the data buffer
+        let mut value_type = 0;
+        let mut value_len = 0;
+
+        let rv = unsafe {
+            RegGetValueW(
+                self.handle,
+                std::ptr::null(), // subkey
+                win32_value_name.as_ptr(),
+                RRF_RT_REG_BINARY | RRF_RT_REG_DWORD | RRF_RT_REG_SZ,
+                &mut value_type,
+                std::ptr::null_mut(), // no data ptr, just query length & type
+                &mut value_len,
+            )
+        }
+        .try_into()
+        .unwrap();
+
+        if rv == ERROR_FILE_NOT_FOUND {
+            return Ok(None);
+        }
+
+        if rv != ERROR_SUCCESS || value_len == 0 {
+            return Err(DetectConflictError::RegGetValueLenFailed(rv));
+        }
+
+        if value_type == REG_SZ {
+            // buffer length is in wide characters
+            let buffer_len = value_len / 2;
+
+            assert_eq!(buffer_len * 2, value_len);
+
+            let mut buffer = vec![0u16; buffer_len.try_into().unwrap()];
+
+            let rv = unsafe {
+                RegGetValueW(
+                    self.handle,
+                    std::ptr::null(), // subkey
+                    win32_value_name.as_ptr(),
+                    RRF_RT_REG_SZ,
+                    std::ptr::null_mut(), // no need to query type again
+                    buffer.as_mut_ptr().cast(),
+                    &mut value_len,
+                )
+            }
+            .try_into()
+            .unwrap();
+
+            if rv != ERROR_SUCCESS {
+                return Err(DetectConflictError::RegGetValueFailed(rv));
+            }
+
+            Ok(Some(RegValue::String(from_win32_string(&buffer))))
+        } else if value_type == REG_BINARY {
+            let mut buffer = vec![0u8; value_len.try_into().unwrap()];
+
+            let rv = unsafe {
+                RegGetValueW(
+                    self.handle,
+                    std::ptr::null(), // subkey
+                    win32_value_name.as_ptr(),
+                    RRF_RT_REG_BINARY,
+                    std::ptr::null_mut(), // no need to query type again
+                    buffer.as_mut_ptr().cast(),
+                    &mut value_len,
+                )
+            }
+            .try_into()
+            .unwrap();
+
+            if rv != ERROR_SUCCESS {
+                return Err(DetectConflictError::RegGetValueFailed(rv));
+            }
+
+            Ok(Some(RegValue::Binary(buffer)))
+        } else if value_type == REG_DWORD {
+            assert_eq!(value_len, 4);
+
+            let mut buffer = 0u32;
+
+            let rv = unsafe {
+                RegGetValueW(
+                    self.handle,
+                    std::ptr::null(), // subkey
+                    win32_value_name.as_ptr(),
+                    RRF_RT_REG_DWORD,
+                    std::ptr::null_mut(), // no need to query type again
+                    (&mut buffer as *mut u32).cast(),
+                    &mut value_len,
+                )
+            }
+            .try_into()
+            .unwrap();
+
+            if rv != ERROR_SUCCESS {
+                return Err(DetectConflictError::RegGetValueFailed(rv));
+            }
+
+            Ok(Some(RegValue::Dword(buffer)))
+        } else {
+            Err(DetectConflictError::UnsupportedValueType(value_type))
+        }
+    }
+    /// Get an iterator that returns the names of all the subkeys of this key
+    pub fn subkey_names(&self) -> SubkeyNames<'_> {
+        SubkeyNames::new(self)
+    }
+}
+
+impl Drop for RegKey {
+    fn drop(&mut self) {
+        assert!(!self.handle.is_null());
+
+        if self.handle == HKEY_LOCAL_MACHINE {
+            return;
+        }
+
+        let rv: u32 = unsafe { RegCloseKey(self.handle) }.try_into().unwrap();
+
+        if rv != ERROR_SUCCESS {
+            log::warn!("failed to close opened registry key");
+        }
+    }
+}
+
+/// An iterator through the subkeys of a key
+///
+/// Returns items of type `Result<OsString, DetectConflictError>`. If an error occurs, calling `next()` again
+/// will likely just continue to result in errors, so it's best to just abandon ship at that
+/// point
+#[derive(Debug)]
+pub struct SubkeyNames<'a> {
+    /// The key that is being iterated
+    key: &'a RegKey,
+    /// The current index of the subkey -- Incremented each successful call to `next()`
+    index: u32,
+    /// A buffer that is large enough to hold the longest subkey name
+    buffer: Option<Vec<u16>>,
+}
+
+impl<'a> SubkeyNames<'a> {
+    /// Create a new subkey name iterator
+    fn new(key: &'a RegKey) -> SubkeyNames<'a> {
+        SubkeyNames {
+            key,
+            index: 0,
+            buffer: None,
+        }
+    }
+    /// Initialize `self.buffer` with a vector that's long enough to hold the longest subkey name
+    /// (if it isn't already)
+    fn create_buffer_if_needed(&mut self) -> Result<(), DetectConflictError> {
+        if self.buffer.is_some() {
+            return Ok(());
+        }
+
+        let mut max_key_length = 0;
+
+        let rv = unsafe {
+            RegQueryInfoKeyW(
+                self.key.handle,
+                std::ptr::null_mut(), // class ptr
+                std::ptr::null_mut(), // class len ptr
+                std::ptr::null_mut(), // reserved
+                std::ptr::null_mut(), // num of subkeys ptr
+                &mut max_key_length,
+                std::ptr::null_mut(), // max class length ptr
+                std::ptr::null_mut(), // number of values ptr
+                std::ptr::null_mut(), // longest value name ptr
+                std::ptr::null_mut(), // longest value data ptr
+                std::ptr::null_mut(), // DACL ptr
+                std::ptr::null_mut(), // last write time ptr
+            )
+        }
+        .try_into()
+        .unwrap();
+
+        if rv != ERROR_SUCCESS {
+            return Err(DetectConflictError::RegQueryInfoKeyFailed(rv));
+        }
+
+        // +1 for the null terminator
+        let max_key_length = usize::try_from(max_key_length).unwrap() + 1;
+
+        self.buffer = Some(vec![0u16; max_key_length]);
+
+        Ok(())
+    }
+}
+
+impl<'a> Iterator for SubkeyNames<'a> {
+    type Item = Result<OsString, DetectConflictError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Err(e) = self.create_buffer_if_needed() {
+            return Some(Err(e));
+        }
+
+        let buffer = self.buffer.as_mut().unwrap();
+        let mut name_len = u32::try_from(buffer.len()).unwrap();
+
+        let rv = unsafe {
+            RegEnumKeyExW(
+                self.key.handle,
+                self.index,
+                buffer.as_mut_ptr(),
+                &mut name_len,
+                std::ptr::null_mut(), // reserved
+                std::ptr::null_mut(), // class ptr
+                std::ptr::null_mut(), // class len ptr
+                std::ptr::null_mut(), // last write time ptr
+            )
+        }
+        .try_into()
+        .unwrap();
+
+        if rv == ERROR_NO_MORE_ITEMS {
+            return None;
+        }
+
+        if rv != ERROR_SUCCESS {
+            return Some(Err(DetectConflictError::RegEnumKeyFailed(rv)));
+        }
+
+        self.index += 1;
+
+        // +1 for the null terminator
+        let name_len = usize::try_from(name_len).unwrap() + 1;
+
+        Some(Ok(from_win32_string(&buffer[0..name_len])))
+    }
+}
+
+/// A single value in the registry
+#[derive(Clone, Debug, PartialEq)]
+pub enum RegValue {
+    /// A REG_BINARY value
+    Binary(Vec<u8>),
+    /// A REG_DWORD value
+    Dword(u32),
+    /// A REG_SZ value
+    String(OsString),
+}
+
+/// Convert an OsStr to a null-terminated wide character string
+///
+/// The input string must not contain any interior null values, and the resulting wide
+/// character array will have a null terminator appended
+fn to_win32_string(s: &OsStr) -> Vec<u16> {
+    // +1 for the null terminator
+    let mut result = Vec::with_capacity(s.len() + 1);
+
+    for wc in s.encode_wide() {
+        assert_ne!(wc, 0);
+        result.push(wc);
+    }
+
+    result.push(0);
+    result
+}
+
+/// Convert a null-terminated wide character string into an OsString
+///
+/// The passed-in slice must have exactly one wide null character as the last element
+fn from_win32_string(s: &[u16]) -> OsString {
+    for (idx, wc) in s.iter().enumerate() {
+        if *wc == 0 {
+            assert_eq!(idx, s.len() - 1);
+            return OsString::from_wide(&s[0..idx]);
+        }
+    }
+    panic!("missing null terminator at end of win32 string");
+}
diff --git a/toolkit/xre/detect_win32k_conflicts/tests/basic.rs b/toolkit/xre/detect_win32k_conflicts/tests/basic.rs
new file mode 100644
index 0000000000..d16a0bd976
--- /dev/null
+++ b/toolkit/xre/detect_win32k_conflicts/tests/basic.rs
@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use detect_win32k_conflicts::{detect_win32k_conflicting_mitigations, ConflictingMitigationStatus};
+
+#[test]
+fn basic() {
+    let mut status = ConflictingMitigationStatus::default();
+
+    let result = unsafe { detect_win32k_conflicting_mitigations(&mut status) };
+
+    assert!(result);
+}