From: Rich Felker <dalias@libc.org>
To: musl@lists.openwall.com
Subject: Re: [PATCH] replace 'hlt' by 'ud2' in i386/x32/x86_64 a_crash implementations
Date: Fri, 17 Apr 2015 16:23:33 -0400 [thread overview]
Message-ID: <20150417202332.GE6817@brightrain.aerifal.cx> (raw)
In-Reply-To: <alpine.LNX.2.11.1504172128260.11963@monopod.intra.ispras.ru>
On Fri, Apr 17, 2015 at 09:48:38PM +0300, Alexander Monakov wrote:
> > > An argument in favor of plain hlt/ud2 is that registers and memory are
> > > preserved, in case someone will be analyzing the coredump.
> >
> > That's a good point. The above could be fixed to preserve registers
> > with some minor added push/pop (simple pusha/popa on 32-bit)
> > before/after the syscall, but then it gets bigger.
>
> Hm, no, I wouldn't like to see that. By the time a_crash executes, "the
> impossible happened", so stack pointer might be pointing somewhere you
> wouldn't want modified.
Given that it's used in C code and C code generally can't be running
at all without a stack, I don't think that's an issue. We're not using
it for detection of stack overflows (which are handled with guard
pages) but for detection of corrupt heap structures, etc. It's
possible that a heap overflow could cause the stack pointer to be
restored to the wrong value, but then I think you would have a really
hard time reaching the a_crash() call.
> A good reason for compilers to generate ud2 is that it also works for kernel
> code, unlike hlt -- but then OSv carries a copy of musl to run it in the
> context of, as I understand, virtualized kernel -- what happens when they
> execute a_crash?
Yes, that does seem like a good aspect.
Rich
prev parent reply other threads:[~2015-04-17 20:23 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-16 17:58 Alexander Monakov
2015-04-17 5:55 ` Rich Felker
2015-04-17 8:12 ` Alexander Monakov
2015-04-17 16:44 ` Rich Felker
2015-04-17 18:48 ` Alexander Monakov
2015-04-17 20:23 ` Rich Felker [this message]
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