8368997: AIX allows reading from address zero which leads to several ubsan findings

[JoKern65]

In _SafeFetchXX_internal() a pointer is checked for readability before using. It returns false if this is not the case. The implementation tries to read from the pointer if this is not feasible the signal handler comes into place jumping back to the function via longjmp, so the _SafeFetchXX_internal() itself can return with a false and a null as pseudo content of the address. If the address was readable the function returns true and provides the content of the address.
Because AIX allows reading from address zero, _SafeFetchXX_internal() returns true and follow up functions using the address are called. All these functions end up in an UBSAN finding regarding reading from zero.
The solution could be to manually code that also AIX behaves like other operating systems and returns false and the content zero in case of address zero. Then no UBSAN finding occur.

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Issue

• JDK-8368997: AIX allows reading from address zero which leads to several ubsan findings (Bug - P4)

Reviewers

• Martin Doerr (@TheRealMDoerr - Reviewer)
• Matthias Baesken (@MBaesken - Reviewer)

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[openjdk]

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8368997: AIX allows reading from address zero which leads to several ubsan findings

Reviewed-by: mdoerr, mbaesken

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At the time when this comment was updated there had been 86 new commits pushed to the master branch:

• 6a4c267: 8365385: [asan] os::pretouch_memory() is not compatible with ASAN
• c669506: 8369277: Remove unused CodeCacheUnloadingTask::_num_workers
• d45e65b: 8030957: AIX: Implement OperatingSystemMXBean.getSystemCpuLoad() and .getProcessCpuLoad() on AIX
• ... and 83 more: https://git.openjdk.org/jdk/compare/3607e9986f1582ebdae1b6ad2a13c1a9c239e0d6...master

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@JoKern65 The following label will be automatically applied to this pull request:

• hotspot-runtime

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[mlbridge]

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• 00: Full (0763a8dd)

[TheRealMDoerr]

I think this is fine. Hotspot should never read from address 0, so returning false should be ok. This essentially emulates the behavior of other operating systems.
Should we only catch adr == nullptr or all addresses within the first memory page?

[JoKern65]

I think this is fine. Hotspot should never read from address 0, so returning false should be ok. This essentially emulates the behavior of other operating systems. Should we only catch adr == nullptr or all addresses within the first memory page?

I would prefer to catch only the nullptr, because this is standard conform.

[JoKern65]

/integrate

[openjdk]

Going to push as commit 692c20c.
Since your change was applied there have been 103 commits pushed to the master branch:

• 285d16a: 8365886: JSplitPane loses track of the left component when the component orientation is changed
• b37a1a3: 8369291: Test java/net/httpclient/http3/H3DataLimitsTest.java fails in quic connection timeout with linux fastdebug builds
• af2fbd5: 8367413: Fix potential truncation error in Arguments::set_heap_size()
• ... and 100 more: https://git.openjdk.org/jdk/compare/3607e9986f1582ebdae1b6ad2a13c1a9c239e0d6...master

Your commit was automatically rebased without conflicts.

[openjdk]

@JoKern65 Pushed as commit 692c20c.

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