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unix: split stack_overflow::install_main_guard by os
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‎std/src/sys/pal/unix/stack_overflow.rs

+115-90
Original file line numberDiff line numberDiff line change
@@ -325,104 +325,129 @@ mod imp {
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})
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}
327327

328+
#[forbid(unsafe_op_in_unsafe_fn)]
328329
unsafe fn install_main_guard() -> Option<Range<usize>> {
329330
let page_size = PAGE_SIZE.load(Ordering::Relaxed);
330-
if cfg!(all(target_os = "linux", not(target_env = "musl"))) {
331-
// Linux doesn't allocate the whole stack right away, and
332-
// the kernel has its own stack-guard mechanism to fault
333-
// when growing too close to an existing mapping. If we map
334-
// our own guard, then the kernel starts enforcing a rather
335-
// large gap above that, rendering much of the possible
336-
// stack space useless. See #43052.
337-
//
338-
// Instead, we'll just note where we expect rlimit to start
339-
// faulting, so our handler can report "stack overflow", and
340-
// trust that the kernel's own stack guard will work.
341-
let stackptr = get_stack_start_aligned()?;
342-
let stackaddr = stackptr.addr();
343-
Some(stackaddr - page_size..stackaddr)
344-
} else if cfg!(all(target_os = "linux", target_env = "musl")) {
345-
// For the main thread, the musl's pthread_attr_getstack
346-
// returns the current stack size, rather than maximum size
347-
// it can eventually grow to. It cannot be used to determine
348-
// the position of kernel's stack guard.
349-
None
350-
} else if cfg!(target_os = "freebsd") {
351-
// FreeBSD's stack autogrows, and optionally includes a guard page
352-
// at the bottom. If we try to remap the bottom of the stack
353-
// ourselves, FreeBSD's guard page moves upwards. So we'll just use
354-
// the builtin guard page.
355-
let stackptr = get_stack_start_aligned()?;
356-
let guardaddr = stackptr.addr();
357-
// Technically the number of guard pages is tunable and controlled
358-
// by the security.bsd.stack_guard_page sysctl.
359-
// By default it is 1, checking once is enough since it is
360-
// a boot time config value.
361-
static PAGES: crate::sync::OnceLock<usize> = crate::sync::OnceLock::new();
362-
363-
let pages = PAGES.get_or_init(|| {
364-
use crate::sys::weak::dlsym;
365-
dlsym!(fn sysctlbyname(*const libc::c_char, *mut libc::c_void, *mut libc::size_t, *const libc::c_void, libc::size_t) -> libc::c_int);
366-
let mut guard: usize = 0;
367-
let mut size = crate::mem::size_of_val(&guard);
368-
let oid = crate::ffi::CStr::from_bytes_with_nul(
369-
b"security.bsd.stack_guard_page\0",
370-
)
371-
.unwrap();
372-
match sysctlbyname.get() {
373-
Some(fcn) => {
374-
if fcn(oid.as_ptr(), core::ptr::addr_of_mut!(guard) as *mut _, core::ptr::addr_of_mut!(size) as *mut _, crate::ptr::null_mut(), 0) == 0 {
375-
guard
376-
} else {
377-
1
378-
}
379-
},
380-
_ => 1,
381-
}
382-
});
383-
Some(guardaddr..guardaddr + pages * page_size)
384-
} else if cfg!(any(target_os = "openbsd", target_os = "netbsd")) {
385-
// OpenBSD stack already includes a guard page, and stack is
386-
// immutable.
387-
// NetBSD stack includes the guard page.
388-
//
389-
// We'll just note where we expect rlimit to start
390-
// faulting, so our handler can report "stack overflow", and
391-
// trust that the kernel's own stack guard will work.
392-
let stackptr = get_stack_start_aligned()?;
393-
let stackaddr = stackptr.addr();
394-
Some(stackaddr - page_size..stackaddr)
395-
} else {
396-
// Reallocate the last page of the stack.
397-
// This ensures SIGBUS will be raised on
398-
// stack overflow.
399-
// Systems which enforce strict PAX MPROTECT do not allow
400-
// to mprotect() a mapping with less restrictive permissions
401-
// than the initial mmap() used, so we mmap() here with
402-
// read/write permissions and only then mprotect() it to
403-
// no permissions at all. See issue #50313.
404-
let stackptr = get_stack_start_aligned()?;
405-
let result = mmap64(
406-
stackptr,
407-
page_size,
408-
PROT_READ | PROT_WRITE,
409-
MAP_PRIVATE | MAP_ANON | MAP_FIXED,
410-
-1,
411-
0,
412-
);
413-
if result != stackptr || result == MAP_FAILED {
414-
panic!("failed to allocate a guard page: {}", io::Error::last_os_error());
331+
332+
unsafe {
333+
// this way someone on any unix-y OS can check that all these compile
334+
if cfg!(all(target_os = "linux", not(target_env = "musl"))) {
335+
install_main_guard_linux(page_size)
336+
} else if cfg!(all(target_os = "linux", target_env = "musl")) {
337+
install_main_guard_linux_musl(page_size)
338+
} else if cfg!(target_os = "freebsd") {
339+
install_main_guard_freebsd(page_size)
340+
} else if cfg!(any(target_os = "netbsd", target_os = "openbsd")) {
341+
install_main_guard_bsds(page_size)
342+
} else {
343+
install_main_guard_default(page_size)
415344
}
345+
}
346+
}
347+
348+
unsafe fn install_main_guard_linux(page_size: usize) -> Option<Range<usize>> {
349+
// Linux doesn't allocate the whole stack right away, and
350+
// the kernel has its own stack-guard mechanism to fault
351+
// when growing too close to an existing mapping. If we map
352+
// our own guard, then the kernel starts enforcing a rather
353+
// large gap above that, rendering much of the possible
354+
// stack space useless. See #43052.
355+
//
356+
// Instead, we'll just note where we expect rlimit to start
357+
// faulting, so our handler can report "stack overflow", and
358+
// trust that the kernel's own stack guard will work.
359+
let stackptr = get_stack_start_aligned()?;
360+
let stackaddr = stackptr.addr();
361+
Some(stackaddr - page_size..stackaddr)
362+
}
416363

417-
let result = mprotect(stackptr, page_size, PROT_NONE);
418-
if result != 0 {
419-
panic!("failed to protect the guard page: {}", io::Error::last_os_error());
364+
unsafe fn install_main_guard_linux_musl(_page_size: usize) -> Option<Range<usize>> {
365+
// For the main thread, the musl's pthread_attr_getstack
366+
// returns the current stack size, rather than maximum size
367+
// it can eventually grow to. It cannot be used to determine
368+
// the position of kernel's stack guard.
369+
None
370+
}
371+
372+
unsafe fn install_main_guard_freebsd(page_size: usize) -> Option<Range<usize>> {
373+
// FreeBSD's stack autogrows, and optionally includes a guard page
374+
// at the bottom. If we try to remap the bottom of the stack
375+
// ourselves, FreeBSD's guard page moves upwards. So we'll just use
376+
// the builtin guard page.
377+
let stackptr = get_stack_start_aligned()?;
378+
let guardaddr = stackptr.addr();
379+
// Technically the number of guard pages is tunable and controlled
380+
// by the security.bsd.stack_guard_page sysctl.
381+
// By default it is 1, checking once is enough since it is
382+
// a boot time config value.
383+
static PAGES: crate::sync::OnceLock<usize> = crate::sync::OnceLock::new();
384+
385+
let pages = PAGES.get_or_init(|| {
386+
use crate::sys::weak::dlsym;
387+
dlsym!(fn sysctlbyname(*const libc::c_char, *mut libc::c_void, *mut libc::size_t, *const libc::c_void, libc::size_t) -> libc::c_int);
388+
let mut guard: usize = 0;
389+
let mut size = crate::mem::size_of_val(&guard);
390+
let oid = crate::ffi::CStr::from_bytes_with_nul(
391+
b"security.bsd.stack_guard_page\0",
392+
)
393+
.unwrap();
394+
match sysctlbyname.get() {
395+
Some(fcn) => {
396+
if fcn(oid.as_ptr(), core::ptr::addr_of_mut!(guard) as *mut _, core::ptr::addr_of_mut!(size) as *mut _, crate::ptr::null_mut(), 0) == 0 {
397+
guard
398+
} else {
399+
1
400+
}
401+
},
402+
_ => 1,
420403
}
404+
});
405+
Some(guardaddr..guardaddr + pages * page_size)
406+
}
421407

422-
let guardaddr = stackptr.addr();
408+
unsafe fn install_main_guard_bsds(page_size: usize) -> Option<Range<usize>> {
409+
// OpenBSD stack already includes a guard page, and stack is
410+
// immutable.
411+
// NetBSD stack includes the guard page.
412+
//
413+
// We'll just note where we expect rlimit to start
414+
// faulting, so our handler can report "stack overflow", and
415+
// trust that the kernel's own stack guard will work.
416+
let stackptr = get_stack_start_aligned()?;
417+
let stackaddr = stackptr.addr();
418+
Some(stackaddr - page_size..stackaddr)
419+
}
423420

424-
Some(guardaddr..guardaddr + page_size)
421+
unsafe fn install_main_guard_default(page_size: usize) -> Option<Range<usize>> {
422+
// Reallocate the last page of the stack.
423+
// This ensures SIGBUS will be raised on
424+
// stack overflow.
425+
// Systems which enforce strict PAX MPROTECT do not allow
426+
// to mprotect() a mapping with less restrictive permissions
427+
// than the initial mmap() used, so we mmap() here with
428+
// read/write permissions and only then mprotect() it to
429+
// no permissions at all. See issue #50313.
430+
let stackptr = get_stack_start_aligned()?;
431+
let result = mmap64(
432+
stackptr,
433+
page_size,
434+
PROT_READ | PROT_WRITE,
435+
MAP_PRIVATE | MAP_ANON | MAP_FIXED,
436+
-1,
437+
0,
438+
);
439+
if result != stackptr || result == MAP_FAILED {
440+
panic!("failed to allocate a guard page: {}", io::Error::last_os_error());
441+
}
442+
443+
let result = mprotect(stackptr, page_size, PROT_NONE);
444+
if result != 0 {
445+
panic!("failed to protect the guard page: {}", io::Error::last_os_error());
425446
}
447+
448+
let guardaddr = stackptr.addr();
449+
450+
Some(guardaddr..guardaddr + page_size)
426451
}
427452

428453
#[cfg(any(target_os = "macos", target_os = "openbsd", target_os = "solaris"))]

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