Re: [RFC] Enable nxstack by default

Hi,

On Tue, Oct 18, 2011 at 11:44 AM, Garrett Cooper <yanegomi_at_gmail.com> wrote:
> On Tue, 18 Oct 2011, Arnaud Lacombe wrote:
>
>> Hi,
>>
>> On Tue, Oct 18, 2011 at 5:07 AM, Kostik Belousov <kostikbel_at_gmail.com>
>> wrote:
>>>
>>> On Mon, Oct 17, 2011 at 09:30:56PM +0200, Oliver Pinter wrote:
>>>>
>>>> Hi all!
>>>>
>>>> I think, it's the time to enable the nxstack feature. Any comments,
>>>> pros, cons?
>>>
>>> I dragged the change long enough for it to miss the 9.0.
>>> After the 9.0 is released, I will flip the switch with the following
>>> change.
>>>
>>> diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c
>>> index 8455f48..926fe64 100644
>>> --- a/sys/kern/imgact_elf.c
>>> +++ b/sys/kern/imgact_elf.c
>>> _at__at_ -118,7 +118,12 _at__at_ static int elf_legacy_coredump = 0;
>>>  SYSCTL_INT(_debug, OID_AUTO, __elfN(legacy_coredump), CTLFLAG_RW,
>>>     &elf_legacy_coredump, 0, "");
>>>
>>> -static int __elfN(nxstack) = 0;
>>> +int __elfN(nxstack) =
>>> +#if defined(__amd64__) || defined(__powerpc64__) /* both 64 and 32 bit
>>> */
>>>
>> Why leaving 32bits x86 CPU supporting the NX feature behind ?
>
> Most likely because it was assumed that i386 doesn't fully support it.
> According to ye great Wikipedia, NX support didn't roll into i386 until
> Prescott, which was pretty late in the non-64-bit capable family of CPUs, as
> its successor -- Conroe -- was 64-bit. Intel detuned some of the early Dual
> Core Pentiums, e.g. the Yonahs to not talk 64-bit. Not sure about AMD.
>
> There are probably more details in binutils, gcc, etc, that I'm missing and
> Kostik can expound on.
>
NX support is advertised in the cpuid flags, just add the logic to
handle this interface. Kostik's patch is just incomplete, but he's got
a commit bit so he can commit it as-is, as he will.

If nonexec_stack becomes the default, it should be on every CPU
supporting the feature, not just the low-hanging one.

 - Arnaud