RFR: JDK-8277029: JMM GetDiagnosticXXXInfo APIs should verify output array sizes [v2]

[Thomas Stuefe]

On Tue, 16 Nov 2021 06:26:08 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> jmm_GetDiagnosticCommandArgumentsInfo and jmm_GetDiagnosticCommandInfo are used to query the hotspot about diagnostic commands. They provide output arrays for the information:
>> 
>> 
>> void jmm_GetDiagnosticCommandArgumentsInfo(JNIEnv *env,
>>           jstring command, dcmdArgInfo* infoArray)
>> 
>> 
>> but array size is implicitly assumed to be known to both caller and callee. Caller and callee negotiate those sizes in prior steps, but things can go wrong. E.g. I recently hunted a bug where `DCmd::number_arguments()` was off - did not reflect the real number of its jcmd parameters - which led to a hidden memory overwriter.
>> 
>> Thankfully, JDK-8264565 rewrote the dcmd framework to deal with this particular issue (The VM I analyzed was older). Still, it would be good if we had additional safety measures here.
>> 
>> -------------
>> 
>> Testing:
>> - manual tests with artificially induced error in one dcmd for debug, release
>> - GHAs (which include tier1 serviceability jcmd tests which use JMX and exercise these APIs)
>
> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove changes to GetDiagnosticCommandInfo

Thanks David and Serguey

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PR: https://git.openjdk.java.net/jdk/pull/6363