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Fix stack overflow detection on FreeBSD 11.1+ #83771

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Apr 2, 2021
Merged

Fix stack overflow detection on FreeBSD 11.1+ #83771

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23 changes: 16 additions & 7 deletions library/std/src/sys/unix/thread.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -343,6 +343,20 @@ pub mod guard {
// it can eventually grow to. It cannot be used to determine
// the position of kernel's stack guard.
None
} else if cfg!(target_os = "freebsd") {
// FreeBSD's stack autogrows, and optionally includes a guard page
// at the bottom. If we try to remap the bottom of the stack
// ourselves, FreeBSD's guard page moves upwards. So we'll just use
// the builtin guard page.
let stackaddr = get_stack_start_aligned()?;
let guardaddr = stackaddr as usize;
// Technically the number of guard pages is tunable and controlled
// by the security.bsd.stack_guard_page sysctl, but there are
// few reasons to change it from the default. The default value has
// been 1 ever since FreeBSD 11.1 and 10.4.
const GUARD_PAGES: usize = 1;
let guard = guardaddr..guardaddr + GUARD_PAGES * page_size;
Some(guard)
} else {
// Reallocate the last page of the stack.
// This ensures SIGBUS will be raised on
Expand Down Expand Up @@ -371,9 +385,8 @@ pub mod guard {
}

let guardaddr = stackaddr as usize;
let offset = if cfg!(target_os = "freebsd") { 2 } else { 1 };

Some(guardaddr..guardaddr + offset * page_size)
Some(guardaddr..guardaddr + page_size)
}
}

Expand Down Expand Up @@ -417,11 +430,7 @@ pub mod guard {
assert_eq!(libc::pthread_attr_getstack(&attr, &mut stackaddr, &mut size), 0);

let stackaddr = stackaddr as usize;
ret = if cfg!(target_os = "freebsd") {
// FIXME does freebsd really fault *below* the guard addr?
let guardaddr = stackaddr - guardsize;
Some(guardaddr - PAGE_SIZE.load(Ordering::Relaxed)..guardaddr)
} else if cfg!(target_os = "netbsd") {
ret = if cfg!(any(target_os = "freebsd", target_os = "netbsd")) {
Some(stackaddr - guardsize..stackaddr)
} else if cfg!(all(target_os = "linux", target_env = "musl")) {
Some(stackaddr - guardsize..stackaddr)
Expand Down