RFR: 8306561: Possible out of bounds access in print_pointer_information [v2]

[Thomas Obermeier]

> 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 one additional commit since the last revision:

  8306561: move solution to caller

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/16381/files
  - new: https://git.openjdk.org/jdk/pull/16381/files/0e45bef8..1a078ab5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16381&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16381&range=00-01

  Stats: 6 lines in 2 files changed: 1 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16381.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16381/head:pull/16381

PR: https://git.openjdk.org/jdk/pull/16381