[foreign-memaccess] RFR 8227107: Add missing toString implementation to MemorySegmentImp

[Maurizio Cimadamore]

Webrev: http://cr.openjdk.java.net/~mcimadamore/panama/8227107_v2/

Maurizio

On 03/07/2019 12:22, Maurizio Cimadamore wrote:
> Here's another version of the webrev which creates a random segment id.
>
> It does that by hashing (via Objects.hash) a random nonce (which 
> changes on every VM execution), the segment address and the hash of 
> the segment base object (if any).
>
> The absolute value of the result is computed, so that we get some 
> positive number (we don't really care about collisions here as much as 
> we do for obfuscation).
>
> This gives an ID which should be pretty innocuous, but useful in most 
> debugging cases.
>
> Thoughts?
>
> (I deliberately wanted to avoid dependencies on heavier crypto APIs, 
> given that this code eventually will live in java.base; I could of 
> course recover some of the murmur hash32 stuff that was dropped as 
> part of this changeset [1], but maybe simpler is better here?)
>
> [1] - http://hg.openjdk.java.net/jdk/jdk/rev/a24e00a7c5ae
>
> Maurizio
>
> On 02/07/2019 22:08, Maurizio Cimadamore wrote:
>>
>> On 02/07/2019 21:58, John Rose wrote:
>>> On Jul 2, 2019, at 9:29 AM, Maurizio Cimadamore 
>>> <maurizio.cimadamore at oracle.com 
>>> <mailto:maurizio.cimadamore at oracle.com>> wrote:
>>>>
>>>> toString() method can't reveal sensitive pointer info
>>>
>>> I wonder if there is a way to sanitize the pointer value, into a 
>>> hash code.
>>> Some JVMs use the raw object address as an input to the identity 
>>> hash code.
>>> We could do something similar.  The hash could be kept small, to 
>>> (say) 5 hex digits,
>>> and would serve to separate the segments for debugging purposes.
>>> Since the default Object.toString does something like this I'm 
>>> thinking we could
>>> emulate that.
>>>
>>> (How to hash the address?  First take a 64-bit address and another 
>>> 64 bits of
>>> nonce secret to the current JVM instance.  Then mix them together, 
>>> using
>>> xxhash or a similar algorithm.  Then throw away all but a few, say 
>>> 20, bits
>>> of result.  The result will provide no useful information to 
>>> attackers, other than
>>> a likely discrimination between different base pointers.)
>>>
>> That's a nice suggestion!
>>
>> Maurizio
>>
>>>
>>>
>>>