RFR: JDK-8230413: Support Pre JDK 6 class with CDS

[Harold Seigel]

Hi Jiangli,

I think this change is going in the wrong direction.  We are trying to 
discourage disabling verification, not encourage it.  We also do not 
want to create more use-cases for preserving -Xverify:none.

It looks like your change would allow archiving of unverified pre-JDK6 
classes, but not allow archiving of verified pre-JDK6 classes.  If so, 
that seems backward.

Thanks, Harold

On 11/11/2019 11:53 PM, Ioi Lam wrote:
> I wonder if there's a safer alternative. Are there tools that can add 
> stackmaps to pre-JDK6 classes? That way they can be verified with the 
> split verifier during CDS dump time.
>
> Thanks
> - Ioi
>
> On 11/11/19 4:25 PM, Jiangli Zhou wrote:
>> Hi David,
>>
>> Thanks for quick response!
>>
>> On Mon, Nov 11, 2019 at 3:12 PM David Holmes 
>> <david.holmes at oracle.com> wrote:
>>> Hi Jiangli,
>>>
>>> On 12/11/2019 8:12 am, Jiangli Zhou wrote:
>>>> Please review the following change that allows archiving
>>>> pre-JAVA_6_VERSION classes with -Xverify:none.
>>>>
>>>> webrev: http://cr.openjdk.java.net/~jiangli/8230413/webrev.00/
>>>> RFE: https://bugs.openjdk.java.net/browse/JDK-8230413
>>>>
>>>> Currently there are still large number of existing classes (pre-built)
>>>> with older class versions (< 50) in real world applications. Those
>>>> classes are missing the benefit of archiving. Particularly, in some
>>>> use cases, class verification can be safely disabled. For those use
>>>> cases, supporting archiving pre JDK 6 classes shows good performance
>>>> benefit. We can re-evaluate this support when -Xverify:none is removed
>>>> in the future, hopefully the needs for supporting class version < 50
>>>> is no longer significant at that time.
>>>>
>>>> This change brings back the pre-JDK-8198849 behavior. Runtime makes
>>>> sure the dump-time verification mode must be the same or stronger than
>>>> the current mode.
>>>>
>>>> A CSR may be needed for the change. Any thoughts on that?
>>> A CSR request is definitely required given that you are proposing to
>>> undo a change that was itself put in place via a CSR request! And given
>>> this is relaxing a "defense-in-depth" check which will result in
>>> increasing exploitability, I think you will need a very strong argument
>>> to justify this.
>> Thanks for confirming this! Will do.
>>
>>> Further this not only undoes JDK-8197972 but it also invalidates
>>> JDK-8155671 being closed as a duplicate of JDK-8197972. JDK-8155671
>>> requested a way to know if verification had been disabled, to help with
>>> analyzing crash reports, but instead we decided to not allow
>>> verification to be disabled.
>> I had some concerns about JDK-8155671 initially before making the
>> change, as it's a closed bug and my memory about the specific issue
>> was flushed out. I brought up the question in the bug. My take on
>> Ioi's response to my query about JDK-8155671 was that the
>> pre-JDK-8197972 behavior would not cause any security hole.
>>
>> Re-evaluating this particular behavior, I think the pre-JDK-8155671
>> would actually matches user intention better. If user decides to turn
>> off verification in safe use cases, it seems to be a good idea to
>> honor that. With the new dynamic archiving capability, archive could
>> be created at the first time when running a particular application.
>> Not forcing verification when user decides to can avoid
>> unnecessary/unwanted overhead.
>>
>> If verification is turned off at dump time for application classes,
>> runtime does not allow execution without also turning off
>> verification. We can determine a crash is not caused by relaxed dump
>> time verification.
>>
>> Regards,
>> Jiangli
>>
>>> David
>>> -----
>>>
>>>
>>>
>>>> Tested with jtreg appcds tests.
>>>>
>>>> Best,
>>>> Jiangli
>>>>
>