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

[Ioi Lam]

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
>>>