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unix: lift init of sigaltstack before sigaction

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This is technically "not necessary", as we will "just" segfault instead
if we e.g. arrive inside the handler fn with the null altstack. However,
it seems incorrect to go about this hoping that segfaulting is okay,
seeing as how our purpose here is to mitigate stack overflow problems.

Make sure NEED_ALTSTACK syncs with PAGE_SIZE when we do.

Co-authored-by: Jonas Böttiger <jonasboettiger@icloud.com>
This commit is contained in:
Jubilee Young 2024-07-16 20:19:16 -07:00
parent 9e354daf7b
commit 357ba1f8ec
1 changed files with 17 additions and 9 deletions
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26
library/std/src/sys/pal/unix/stack_overflow.rs
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@ -123,28 +123,36 @@ mod imp {
static MAIN_ALTSTACK: AtomicPtr<libc::c_void> = AtomicPtr::new(ptr::null_mut());
static NEED_ALTSTACK: AtomicBool = AtomicBool::new(false);
/// # Safety
/// Must be called only once
#[forbid(unsafe_op_in_unsafe_fn)]
pub unsafe fn init() {
PAGE_SIZE.store(os::page_size(), Ordering::Relaxed);
// Always write to GUARD to ensure the TLS variable is allocated.
let guard = install_main_guard().unwrap_or(0..0);
let guard = unsafe { install_main_guard().unwrap_or(0..0) };
GUARD.set((guard.start, guard.end));
let mut action: sigaction = mem::zeroed();
// SAFETY: assuming all platforms define struct sigaction as "zero-initializable"
let mut action: sigaction = unsafe { mem::zeroed() };
for &signal in &[SIGSEGV, SIGBUS] {
sigaction(signal, ptr::null_mut(), &mut action);
// SAFETY: just fetches the current signal handler into action
unsafe { sigaction(signal, ptr::null_mut(), &mut action) };
// Configure our signal handler if one is not already set.
if action.sa_sigaction == SIG_DFL {
if !NEED_ALTSTACK.load(Ordering::Relaxed) {
// haven't set up our sigaltstack yet
NEED_ALTSTACK.store(true, Ordering::Release);
let handler = unsafe { make_handler(true) };
MAIN_ALTSTACK.store(handler.data, Ordering::Relaxed);
mem::forget(handler);
}
action.sa_flags = SA_SIGINFO | SA_ONSTACK;
action.sa_sigaction = signal_handler as sighandler_t;
sigaction(signal, &action, ptr::null_mut());
NEED_ALTSTACK.store(true, Ordering::Relaxed);
// SAFETY: only overriding signals if the default is set
unsafe { sigaction(signal, &action, ptr::null_mut()) };
}
}
let handler = make_handler(true);
MAIN_ALTSTACK.store(handler.data, Ordering::Relaxed);
mem::forget(handler);
}
pub unsafe fn cleanup() {