Integrated: 8318737: Fallback linker passes bad JNI handle

[Jorn Vernee]

On Tue, 24 Oct 2023 17:01:35 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> The result of `FindClass` is a local JNI handle (in `find_class_from_class_loader`, called from `jni_FindClass` [1]). As such, we need to wrap the return value of `FindClass` in a global reference when storing it inside fallbackLinker.c.
> 
> While investigating this, I also noticed an existing bug in `JNIHandles::handle_type`. This method is used from the implementation of `GetObjectRefType` ([2]), and from the implementation of `-Xcheck:jni` code. The former specifies that `JNIInvalidRefType` is a valid return value, and the latter compares the result against `JNIInvalidRefType`. However, if the handle is not any valid type, the implementation bottoms out in a `ShouldNotReachHere()`, meaning `JNIHandles::handle_type` can never return `JNIInvalidRefType`. I've fixed this by letting the enclosing if/else chain fall through to just returning the default result, which is `JNIInvalidRefType`. In that case, I observe the expected stack trace when running with `-Xcheck:jni`. For example:
> 
> 
> FATAL ERROR in native method: Bad global or local ref passed to JNI
>         at jdk.internal.foreign.abi.fallback.LibFallback.doDowncall(java.base at 22-internal/Native Method)
>         at jdk.internal.foreign.abi.fallback.LibFallback.doDowncall(java.base at 22-internal/LibFallback.java:94)
>         at jdk.internal.foreign.abi.fallback.FallbackLinker.doDowncall(java.base at 22-internal/FallbackLinker.java:197)
>         at java.lang.invoke.LambdaForm$DMH/0x000001b585008000.invokeStaticInit(java.base at 22-internal/LambdaForm$DMH)
>         at java.lang.invoke.LambdaForm$MH/0x000001b585029400.invoke(java.base at 22-internal/LambdaForm$MH)
>         at java.lang.invoke.LambdaForm$MH/0x000001b58502d000.invokeExact_MT(java.base at 22-internal/LambdaForm$MH)
>         at TestUpcallDeopt.payload(TestUpcallDeopt.java:93)
>         at TestUpcallDeopt.main(TestUpcallDeopt.java:84)
>         at java.lang.invoke.LambdaForm$DMH/0x000001b585006800.invokeStatic(java.base at 22-internal/LambdaForm$DMH)
>         at java.lang.invoke.LambdaForm$MH/0x000001b58502a800.invoke(java.base at 22-internal/LambdaForm$MH)
>         at java.lang.invoke.Invokers$Holder.invokeExact_MT(java.base at 22-internal/Invokers$Holder)
>         at jdk.internal.reflect.DirectMethodHandleAccessor.invokeImpl(java.base at 22-internal/DirectMethodHandleAccessor.java:154)
>         at jdk.internal.reflect.DirectMethodHandleAccessor.invoke(java.base at 22-internal/DirectMethodHandleAccessor.java:103)
>         at java.lang.reflect.Method.invoke(java.base at 22-internal/Method.java:580...

This pull request has now been integrated.

Changeset: 3885dc5b
Author:    Jorn Vernee <jvernee at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/3885dc5b9acf08dc90397ab02b814bc72d7b4ed5
Stats:     38 lines in 7 files changed: 22 ins; 6 del; 10 mod

8318737: Fallback linker passes bad JNI handle

Reviewed-by: alanb

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PR: https://git.openjdk.org/jdk/pull/16349