RFR: 8277204: Implementation of JEP 8264130: PAC-RET protection for Linux/AArch64 [v14]

[David Holmes]

On Tue, 1 Feb 2022 11:05:46 GMT, Alan Hayward <duke at openjdk.java.net> wrote:

>> src/hotspot/cpu/aarch64/vm_version_aarch64.cpp line 429:
>> 
>>> 427: #else
>>> 428:     warning("UseROPProtection specified, but not supported in the VM.");
>>> 429: #endif
>> 
>> If we issue these warnings should `_rop_protection` still be set true?
>
> As per this conversation: https://github.com/openjdk/jdk/pull/6334#discussion_r791722292
> 
> The idea was, the user is explicitly asking for asking for pac-ret so we should honour that. Whereas standard would only enable what is supported for that system.

But we can't honour that because it is not supported. Further, the suggestion in the referenced discussion seemed to be based on the assumption that doing so would be harmless because it is NOP based, but you have indicated that may not be the case and so it may actually lead to a crash!

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PR: https://git.openjdk.java.net/jdk/pull/6334