Re: [PATCH v4 7/7] selftests/x86: Add a userspace test for LASS enforcement

[Sohil Mehta <sohil.mehta@intel.com>]

> 
>> +int main(void)
>> +{
>> +	ksft_print_header();
>> +
>> +	if (!is_lass_active())
>> +		ksft_exit_skip("LASS is not enabled\n");
>> +
>> +	ksft_set_plan(TOTAL_TESTS);
>> +
>> +	sethandler(SIGSEGV, fault_handler, 0);
>> +	/* Only to report a #SS; LASS shouldn't cause one here. */
>> +	sethandler(SIGBUS, fault_handler, 0);
> 
> So the purpose is that if there is an unexpected #SS, fails the test instead of
> killing it, right?
> 

Sorry, I missed this question earlier. Yes, the goal is to catch the
SIGBUS and report a failure.

I think it isn't worth keeping in the first place. My initial plan was
to trigger an LASS violation #SS. But, it turned out to be much harder
to trigger. I'll probably remove it because it creates a distraction.

>> +
>> +	ksft_print_msg("Accessing the kernel address 0x%lx from userspace\n",
>> +		       (unsigned long)KERNEL_ADDR);
>> +	test_kernel_read();
>> +	test_kernel_write();
>> +	test_kernel_fetch();
>> +
>> +	clearhandler(SIGBUS);
>> +	clearhandler(SIGSEGV);
>> +
>> +	ksft_finished();
>> +}
>