RFR: 8345296: AArch64: VM crashes with SIGILL when prctl is disallowed

[Andrew Haley]

On Mon, 2 Dec 2024 12:17:26 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> We have caught this in some prod environments, where `prctl` is forbidden by the sandboxing mechanism. This fails the JVM, because we have the following code to check for SVE vector length:
> 
> 
> int VM_Version::get_current_sve_vector_length() {
>   assert(VM_Version::supports_sve(), "should not call this");
>   return prctl(PR_SVE_GET_VL);
> }
> 
> 
> That code returns `-1` when `prctl` is disallowed, which JVM then blindly interprets as vector length, leading to `SIGILL`. I looked around other uses of `prctl` around Hotspot, and they all seem to handle the errors correctly.
> 
> Additional testing:
>  - [x] Linux AArch64 server fastdebug, with seccomp reproducer
>  - [ ] Linux AArch64 server fastdebug, `all`

Huh. That's annoying.
Does this patch mean that a warning is printed unconditionally on systems where `prctl` is disabled?

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PR Comment: https://git.openjdk.org/jdk/pull/22479#issuecomment-2511573977