On Mon, 11 Aug 2025 12:35:07 GMT, Per Minborg <[email protected]> wrote:
>> ### Description
>> This PR proposes to update the `ClassLoader` implementation to properly
>> guard access to the provided `ByteBuffer` when defining a class using
>> `defineClass(String, ByteBuffer, ...)`. Specifically, calls to
>> `SharedSecrets.getJavaNioAccess().acquireSession(ByteBuffer)` and
>> `releaseSession(ByteBuffer)` have been introduced to ensure safe and
>> consistent buffer access throughout the native class definition process,
>> even in the case of a `ByteBuffer` is backed by a `MemorySegment`.
>>
>> ### Impact
>> This modification is internal to the `ClassLoader` implementation and does
>> not affect the public API.
>> Improves the robustness and security of class loading from buffers.
>>
>> ### Testing
>> Tier 1, 2, and 3 JDK tests pass on multiple platforms.
>
> test/jdk/java/lang/ClassLoader/defineClass/GuardByteBuffer.java line 43:
>
>> 41:
>> 42: @Test
>> 43: void guardCrash() throws InterruptedException {
>
> I was not able to reproduce the crash using this test on a Mac. The original
> reproducer worked on a Windows machine.
Hello Per, I too couldn't reproduce the crash from the original reproducer (and
this test) on macos and I found that a bit odd. I read up a bit about macos
memory debugging tools and it turns out macos has a "Guard Malloc"
implementation
https://developer.apple.com/library/archive/documentation/Performance/Conceptual/ManagingMemory/Articles/MallocDebug.html
which can be optionally enabled to debug issues like these. `man libgmalloc`
has additional details about it.
So I ran the original reproducer again, this time with:
```
export DYLD_INSERT_LIBRARIES=/usr/lib/libgmalloc.dylib
java ... <that-reproducer>
and that consistently reproduces the crash on macos. I will build this PR
locally and give it a try soon to make sure the crash no longer reproduces.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/26724#discussion_r2293850857
