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Rollup merge of #69969 - iximeow:sigstack-guard-page, r=cuviper

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unix: Set a guard page at the end of signal stacks

This mitigates possible issues when signal stacks overflow, which could
manifest as segfaults or in unlucky circumstances possible clobbering of
other memory values as stack overflows tend to enable.

I went ahead and made a PR for this because it's a pretty small change, though if I should open an issue/RFC for this and discuss there first I'll happily do so. I've also added some example programs that demonstrate the uncomfortably clobber-happy behavior we currently have, and the segfaults that could/should result instead, [here](https://github.com/iximeow/jubilant-train).
This commit is contained in:
Mazdak Farrokhzad 2020-03-19 06:57:37 +01:00 • committed by GitHub
commit 4c3a5a5da6
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1 changed files with 18 additions and 5 deletions
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23
src/libstd/sys/unix/stack_overflow.rs
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@ -45,8 +45,9 @@ mod imp {
use libc::{mmap, munmap};
use libc::{sigaction, sighandler_t, SA_ONSTACK, SA_SIGINFO, SIGBUS, SIG_DFL};
use libc::{sigaltstack, SIGSTKSZ, SS_DISABLE};
use libc::{MAP_ANON, MAP_PRIVATE, PROT_READ, PROT_WRITE, SIGSEGV};
use libc::{MAP_ANON, MAP_PRIVATE, PROT_NONE, PROT_READ, PROT_WRITE, SIGSEGV};
use crate::sys::unix::os::page_size;
use crate::sys_common::thread_info;
#[cfg(any(target_os = "linux", target_os = "android"))]
@ -137,12 +138,22 @@ mod imp {
}
unsafe fn get_stackp() -> *mut libc::c_void {
let stackp =
mmap(ptr::null_mut(), SIGSTKSZ, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
let stackp = mmap(
ptr::null_mut(),
SIGSTKSZ + page_size(),
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON,
-1,
0,
);
if stackp == MAP_FAILED {
panic!("failed to allocate an alternative stack");
}
stackp
let guard_result = libc::mprotect(stackp, page_size(), PROT_NONE);
if guard_result != 0 {
panic!("failed to set up alternative stack guard page");
}
stackp.add(page_size())
}
#[cfg(any(
@ -190,7 +201,9 @@ mod imp {
ss_size: SIGSTKSZ,
};
sigaltstack(&stack, ptr::null_mut());
munmap(handler._data, SIGSTKSZ);
// We know from `get_stackp` that the alternate stack we installed is part of a mapping
// that started one page earlier, so walk back a page and unmap from there.
munmap(handler._data.sub(page_size()), SIGSTKSZ + page_size());
}
}
}