RFR: 8306561: Possible out of bounds access in print_pointer_information [v6]

[Thomas Obermeier]

On Tue, 31 Oct 2023 17:27:57 GMT, Thomas Obermeier <duke at openjdk.org> wrote:

>> MallocTracker::print_pointer_information in src/hotspot/share/services/mallocTracker.cpp is called to check the highest pointer address of the reserved region. To do so it aligns the test pointer down to the next 8 Byte boundary and casts this address to class MallocHeader in order to use this classes eye-catcher member _canary for validation. Method looks_valid() dereferences _canary's content. _canary has an offset of 14 bytes relative to the class. Therefore it resides outside the reserved region for the highest pointer address, which causes a segmentation violation.
>> 
>> We would expect the same error also for other platforms than AIX as memory is read, which is not allocated. Interestingly, Linux seems to allow this access for 5 times 4K above the reserved region.
>> 
>> As a solution, looks_valid() should check _canary's address as being invalid, and return false immediately.
>
> Thomas Obermeier has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Merge branch 'JDK-8306561' of https://github.com/TOatGithub/jdk into JDK-8306561
>  - 8306561: test range instead of endpoints before casting

Checks still run fine with the latest switch to os::is_readable_range. Therefore:

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PR Comment: https://git.openjdk.org/jdk/pull/16381#issuecomment-1790322365