From: Jakub Jelinek <jakub@redhat.com>
To: Jeff Law <law@redhat.com>, Eric Botcazou <ebotcazou@adacore.com>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: RFC: stack/heap collision vulnerability and mitigation with GCC
Date: Mon, 19 Jun 2017 17:29:00 -0000 [thread overview]
Message-ID: <20170619172932.GV2123@tucnak> (raw)
In-Reply-To: <bef46e40-8004-0f80-4928-ad0795eb76ba@redhat.com>
On Mon, Jun 19, 2017 at 11:07:06AM -0600, Jeff Law wrote:
> After much poking around I concluded that we really need to implement
> allocation and probing via a "moving sp" strategy. Probing into
> unallocated areas runs afoul of valgrind, so that's a non-starter.
>
> Allocating stack space, then probing the pages within the space is
> vulnerable to async signal delivery between the allocation point and the
> probe point. If that occurs the signal handler could end up running on
> a stack that has collided with the heap.
>
> Ideally we would allocate and probe a page as an atomic unit (which is
> feasible on PPC). Alternatively, due to ISA restrictions, allocate a
> page, then probe the page as distinct instructions. The latter still
> has a race, but we'd have to take the async signal in a single
> instruction window.
And if the allocation is only a page at a time, the single insn race window
can be mitigated in the kernel (probe (read-only is fine) the word at the
stack when setting up a signal frame for async signal).
> So, time to open the discussion to questions & comments.
>
> I've got patches I need to cleanup and post for comments that implement
> this for x86, ppc, aarch64 and s390. x86 and ppc are IMHO in good
> shape. THere's an unhandled case for s390. I've got evaluation still
> to do on aarch64.
In the patches Jeff is going to post, we have (at least for
-fasynchronous-unwind-tables which is on by default on e.g. x86)
precise unwind info even with the new stack check mode.
ira.c currently has:
/* We need the frame pointer to catch stack overflow exceptions if
the stack pointer is moving (as for the alloca case just above). */
|| (STACK_CHECK_MOVING_SP
&& flag_stack_check
&& flag_exceptions
&& cfun->can_throw_non_call_exceptions)
For alloca we have a frame pointer for other reasons, the question is
if we really need this hunk even if we provided proper unwind info
even for the Ada -fstack-check mode. Or, if we provide proper unwind info
for -fasynchronous-unwind-tables, if the above could not be also
&& !flag_asynchronous_unwind_tables. Eric, what exactly is the reason
for the above, is it just lack of proper CFI notes, or something different?
Also, on i?86 orq $0, (%rsp) or orl $0, (%esp) is used to probe stack,
while it is shorter, is it actually faster or as slow as movq $0, (%rsp)
or movl $0, (%esp) ?
Jakub
next prev parent reply other threads:[~2017-06-19 17:29 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-19 17:07 Jeff Law
2017-06-19 17:29 ` Jakub Jelinek [this message]
2017-06-19 17:45 ` Jeff Law
2017-06-19 17:51 ` Jakub Jelinek
2017-06-19 21:51 ` Jeff Law
2017-06-20 8:03 ` Uros Bizjak
2017-06-20 10:18 ` Richard Biener
2017-06-20 11:10 ` Uros Bizjak
2017-06-20 12:13 ` Florian Weimer
2017-06-20 12:17 ` Uros Bizjak
2017-06-20 12:20 ` Uros Bizjak
2017-06-20 12:27 ` Richard Biener
2017-06-20 21:57 ` Jeff Law
2017-06-20 15:59 ` Jeff Law
2017-06-19 18:00 ` Richard Biener
2017-06-19 18:02 ` Richard Biener
2017-06-19 18:15 ` Florian Weimer
2017-06-19 21:57 ` Jeff Law
2017-06-19 22:08 ` Jeff Law
2017-06-20 7:50 ` Eric Botcazou
2017-06-19 17:51 ` Joseph Myers
2017-06-19 17:55 ` Jakub Jelinek
2017-06-19 18:21 ` Florian Weimer
2017-06-19 21:56 ` Joseph Myers
2017-06-19 22:05 ` Jeff Law
2017-06-19 22:10 ` Florian Weimer
2017-06-19 19:05 ` Jeff Law
2017-06-19 19:45 ` Jakub Jelinek
2017-06-19 21:41 ` Jeff Law
2017-06-20 8:27 ` Richard Earnshaw (lists)
2017-06-20 15:50 ` Jeff Law
2017-06-19 18:12 ` Richard Kenner
2017-06-19 22:05 ` Jeff Law
2017-06-19 22:07 ` Richard Kenner
2017-06-20 8:21 ` Eric Botcazou
2017-06-20 15:50 ` Jeff Law
2017-06-20 19:48 ` Jakub Jelinek
2017-06-20 20:37 ` Eric Botcazou
2017-06-20 20:46 ` Jeff Law
2017-06-20 8:17 ` Eric Botcazou
2017-06-20 21:52 ` Jeff Law
2017-06-20 22:20 ` Eric Botcazou
2017-06-21 17:31 ` Jeff Law
2017-06-21 19:07 ` Florian Weimer
2017-06-21 7:56 ` Andreas Schwab
2017-06-20 9:27 ` Richard Earnshaw (lists)
2017-06-20 21:39 ` Jeff Law
2017-06-21 8:41 ` Richard Earnshaw (lists)
2017-06-21 17:25 ` Jeff Law
2017-06-22 9:53 ` Richard Earnshaw (lists)
2017-06-22 15:30 ` Jeff Law
2017-06-22 16:07 ` Szabolcs Nagy
2017-06-22 16:15 ` Jeff Law
2017-06-28 6:45 ` Florian Weimer
2017-07-13 23:21 ` Jeff Law
2017-07-18 19:54 ` Florian Weimer
2017-06-20 23:22 Wilco Dijkstra
2017-06-21 8:34 ` Richard Earnshaw (lists)
2017-06-21 8:44 ` Andreas Schwab
2017-06-21 8:46 ` Richard Earnshaw (lists)
2017-06-21 8:46 ` Richard Earnshaw (lists)
2017-06-21 9:03 ` Wilco Dijkstra
2017-06-21 17:05 ` Jeff Law
2017-06-21 17:47 ` Wilco Dijkstra
2017-06-22 16:10 ` Jeff Law
2017-06-22 22:57 ` Wilco Dijkstra
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