Check for PaX during initialization

[Mikael Vidstedt]

Fixed and pushed!

Thanks,
Mikael

> On May 3, 2017, at 7:37 PM, David Holmes <david.holmes at oracle.com> wrote:
> 
> Minor typo:
> 
> "so may want" -> "so you may want"
> 
> Cheers,
> David
> 
> On 4/05/2017 2:18 AM, Mikael Vidstedt wrote:
>> 
>> Poonam/David,
>> 
>> Thanks for the reviews and feedback. Updated webrev:
>> 
>> http://cr.openjdk.java.net/~mikael/webrevs/portola/paxcheck/webrev.03/hotspot/webrev/
>> 
>> Incremental from webrev.02:
>> 
>> http://cr.openjdk.java.net/~mikael/webrevs/portola/paxcheck/webrev.03.incr/hotspot/webrev/
>> 
>> Cheers,
>> Mikael
>> 
>>> On May 2, 2017, at 6:36 PM, David Holmes <david.holmes at oracle.com
>>> <mailto:david.holmes at oracle.com>> wrote:
>>> 
>>> Seems okay. You may want to add the paxctl instructions as Poonam
>>> suggested.
>>> 
>>> Thanks,
>>> David
>>> 
>>> On 2/05/2017 7:02 AM, Mikael Vidstedt wrote:
>>>> 
>>>> Please review the following change, which adds code to check for the
>>>> presence of PaX/MPROTECT
>>>> (https://pax.grsecurity.net/docs/mprotect.txt
>>>> <https://pax.grsecurity.net/docs/mprotect.txt>) during VM
>>>> initialization, and prints out a helpful message if PaX is enabled
>>>> and interfering with the VM. Specifically, the code checks if a
>>>> writable page can be made executable (mimicking what the JIT would
>>>> typically do). Since ZERO doesn’t generate code the check is not
>>>> performed there.
>>>> 
>>>> Copy+paste from the actual change:
>>>> // Some linux distributions (notably: Alpine Linux) include the
>>>> // grsecurity in the kernel by default. Of particular interest from a
>>>> // JVM perspective is PaX (https://pax.grsecurity.net/), which adds
>>>> // some security features related to page attributes. Specifically,
>>>> // the MPROTECT PaX functionality
>>>> // (https://pax.grsecurity.net/docs/mprotect.txt) prevents dynamic
>>>> // code generation by disallowing a (previously) writable page to be
>>>> // marked as executable. This is, of course, exactly what HotSpot does
>>>> // for both JIT compiled method, as well as for stubs, adapters, etc.
>>>> //
>>>> // Instead of crashing "lazily" when trying to make a page executable,
>>>> // this code probes for the presence of PaX and reports the failure
>>>> // eagerly.
>>>> 
>>>> http://cr.openjdk.java.net/~mikael/webrevs/portola/paxcheck/webrev.02/hotspot/webrev/
>>>> 
>>>> Cheers,
>>>> Mikael
>>>> 
>>