CONFIG_MODULE_SIG_FORCE can make tests fail

[Po-Hsu Lin]

Issue found on kernel with CONFIG_MODULE_SIG_FORCE=y, it will check the module signature. So the module we build when running the test will be rejected.

The following tests will fail:
  * ubuntu_ltp_kernel_misc
    - fw_load ('insmod' exited with a non-zero code 1 at tst_cmd.c:121)
    - block_dev ('insmod' exited with a non-zero code 1 at tst_cmd.c:121)
    - tpci ('insmod' exited with a non-zero code 1 at tst_cmd.c:121)
    - ltp_acpi ('insmod' exited with a non-zero code 1 at tst_cmd.c:121)
    - uaccess ('insmod' exited with a non-zero code 1 at tst_cmd.c:121)
  * ubuntu_ltp_stable/commands
    - insmod01_sh (insmod: ERROR: could not insert module ltp_insmod01.ko: Key was rejected by service)
  * ubuntu_ltp_syscalls
    - delete_module01 (insmod: ERROR: could not insert module dummy_del_mod.ko: Key was rejected by service)
    - delete_module03 (insmod: ERROR: could not insert module dummy_del_mod.ko: Key was rejected by service)
    - finit_module01 (TFAIL: finit_module(fd, "status=valid", 0) failed: EKEYREJECTED (129))
    - finit_module02 (insmod: ERROR: could not insert module /opt/ltp/testcases/bin/finit_module.ko: Key was rejected by service)
    - init_module01 (TFAIL: init_module(buf, sb.st_size, "status=valid") failed: EKEYREJECTED (129))
    - init_module02 (insmod: ERROR: could not insert module init_module.ko: Key was rejected by service)
  * ubuntu_lttng_smoke_test
    - lttng-smoke-test (Error: Event sched_switch: Kernel tracer not available (channel channel0, session test-kernel-session))
  * ubuntu_qrt_kernel_security
    - KernelSecurityTest.test_072_strict_devmem (insmod: ERROR: could not insert module signpost/signpost.ko: Key was rejected by service)

Note that for the ubuntu_ltp_syscalls tests failure, they just check the /proc/cmdline to see if the module.sig_enforce was added there. As we don't have it in /proc/cmdline, it's expecting the test to pass.

I think azure-fde is affected as well.

It's better to add corresponding config check, and prints an user-friendly error message to make reviewers' life easier.

[Po-Hsu Lin (cypressyew)]

For LTP syscalls - https://lists.linux.it/pipermail/ltp/2024-December/041355.html

[Po-Hsu Lin (cypressyew)]

For ubuntu_ltp_kernel_misc and ubuntu_ltp_stable/commands: https://lists.linux.it/pipermail/ltp/2024-December/041360.html

[Po-Hsu Lin (cypressyew)]

For ubuntu_lttng_smoke_tests:
https://kernel.ubuntu.com/gitea/tnt/autotest-client-tests/pulls/42