Only permit jumps within sub-programs

[Alan-Jowett]

This pull request includes several changes to improve the robustness and functionality of the eBPF verifier and the UBPF virtual machine. The most significant changes involve adding error handling to the fuzzer harness, updating the submodule for the eBPF verifier, and enhancing the UBPF VM to ensure the integrity of sub-programs.

Error Handling Improvements:

• libfuzzer/libfuzz_harness.cc: Added try-catch block in LLVMFuzzerTestOneInput to catch and log exceptions, improving error handling during fuzz testing. [1] [2]

Submodule Update:

• external/ebpf-verifier: Updated the submodule commit to a newer version, likely including various improvements and bug fixes.

UBPF VM Enhancements:

• vm/ubpf_vm.c: Introduced a new function check_for_self_contained_sub_programs to ensure that sub-programs only enter via calls and exit properly, preventing jumps out of one program into another. This change includes several helper functions for sorting and deduplicating arrays. [1] [2] [3]
• Removed checks for undefined behavior related to local function calls, simplifying the code and relying on the new sub-program validation logic. [1] [2]

Test Data Update:

• tests/err-call0.data: Added an error message to the test data to reflect the new validation logic for sub-programs.

[coveralls]

coverage: 79.25% (-0.09%) from 79.342%
when pulling 5bdc413 on Alan-Jowett:issue580
into 29bbad0 on iovisor:main.