Re: Why is irq_stack_union a union?

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: Why is irq_stack_union a union?
Date	2015-09-01 23:50 +0200
Message-ID	<q41Bf-21v-3@gated-at.bofh.it> (permalink)
References	<q3Ev1-2yp-23@gated-at.bofh.it> <q3F7H-3hD-3@gated-at.bofh.it> <q3Fr3-3Tm-9@gated-at.bofh.it> <q3KTM-3lU-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Mon, Aug 31, 2015 at 8:55 PM, Brian Gerst <brgerst@gmail.com> wrote:
> On Mon, Aug 31, 2015 at 6:01 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> On Mon, Aug 31, 2015 at 2:47 PM, Brian Gerst <brgerst@gmail.com> wrote:
>>> On Mon, Aug 31, 2015 at 5:00 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>>> Why not just a struct? Also, why is this all tangled up in gsbase initialization?
>>>
>>> It has to do with the fact that the GCC stackprotector is hardcoded to
>>> look for the canary at %gs:40.  Since we also use %gs for the percpu
>>> segment, we have to make sure that the canary is placed at the start
>>> of the percpu section.  Overlaying it onto the bottom of the IRQ stack
>>> and was the most convenient way to do it, with a side benefit that
>>> overflowing the stack will trip the canary.
>>
>> Would a struct not make more sense, then?
>
> Why would it?  A union shows the overlay better.

I guess you're thinking of it as an overlay and I'm thinking of it as
the layout being the IRQ stack directly above the stack canary.

--Andy

>
> --
> Brian Gerst



-- 
Andy Lutomirski
AMA Capital Management, LLC
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Why is irq_stack_union a union? Andy Lutomirski <luto@amacapital.net> - 2015-08-31 23:10 +0200
  Re: Why is irq_stack_union a union? Brian Gerst <brgerst@gmail.com> - 2015-08-31 23:50 +0200
    Re: Why is irq_stack_union a union? Andy Lutomirski <luto@amacapital.net> - 2015-09-01 00:10 +0200
      Re: Why is irq_stack_union a union? Brian Gerst <brgerst@gmail.com> - 2015-09-01 06:00 +0200
        Re: Why is irq_stack_union a union? Andy Lutomirski <luto@amacapital.net> - 2015-09-01 23:50 +0200

csiph-web