RFR: 8318737: Fallback linker passes bad JNI handle [v2]

[Alan Bateman]

On Wed, 25 Oct 2023 11:16:54 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.invo...
>
> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
> 
>   explicitly propagate fallback library init failures

The changes looks okay to me.

src/java.base/share/classes/jdk/internal/foreign/abi/fallback/LibFallback.java line 49:

> 47:                                 // library failed to initialize. Do not silently mark as unsupported
> 48:                                 throw new ExceptionInInitializerError("Fallback library failed to initialize");
> 49:                             }

It might be better to move this to after the try-catch, if init were to somehow fail with ULE then it suggests something else is wrong.

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Marked as reviewed by alanb (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16349#pullrequestreview-1699749537
PR Review Comment: https://git.openjdk.org/jdk/pull/16349#discussion_r1373235567