Date: Tue, 30 Mar 2021 12:34:55 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Alan Somers <asomers@freebsd.org> Cc: "freebsd-hackers@freebsd.org" <hackers@freebsd.org> Subject: Re: How does the stack's guard page work on amd64? Message-ID: <YGLwv%2BKkmhxeeJUp@kib.kiev.ua> In-Reply-To: <CAOtMX2i5d0c9E=W=S6aKp1j5JczaaTqKDX8kW=2NqF=i35dWog@mail.gmail.com> References: <CAOtMX2i5d0c9E=W=S6aKp1j5JczaaTqKDX8kW=2NqF=i35dWog@mail.gmail.com>
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On Mon, Mar 29, 2021 at 11:06:36PM -0600, Alan Somers wrote: > Rust tries to detect stack overflow and handles it differently than other > segfaults, but it's currently broken on FreeBSD/amd64. I've got a patch > that fixes the problem, but I would like someone to confirm my reasoning. > > It seems like FreeBSD's main thread stacks include a guard page at the > bottom. However, when Rust tries to create its own guard page (by > re-mmap()ping and mprotect()ing it), it seems like FreeBSD's guard page > automatically moves up into the un-remapped region. At least, that's how > it behaves, based on the addresses that segfault. Is that correct? Show the facts. For instance, procstat -v (and a note which mapping was established by runtime for the 'guard') would tell the whole story. My guess would be that procctl(PROC_STACKGAP_CTL, &PROC_STACKGAP_DISABLE) would be enough. Cannot tell without specific data. > > For other threads, Rust doesn't try to remap the guard page, it just relies > on the guard page created by libthr in _thr_stack_alloc. > > Finally, what changed in between FreeBSD 10.3 and 11.4? Rust's stack > overflow detection worked in 10.3. > > -Alan > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org"
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