Re: [RFC PATCH 5/5] selftest/x86: Add CET quick test

[Peter Zijlstra]

On Thu, May 21, 2020 at 02:17:20PM -0700, Yu-cheng Yu wrote:

> +#pragma GCC push_options
> +#pragma GCC optimize ("O0")
> +void ibt_violation(void)
> +{
> +#ifdef __i386__
> +	asm volatile("lea 1f, %eax");
> +	asm volatile("jmp *%eax");
> +#else
> +	asm volatile("lea 1f, %rax");
> +	asm volatile("jmp *%rax");
> +#endif
> +	asm volatile("1:");
> +	result[test_id] = -1;
> +	test_id++;
> +	setcontext(&ucp);
> +}
> +
> +void shstk_violation(void)
> +{
> +#ifdef __i386__
> +	unsigned long x = 0;
> +
> +	((unsigned long *)&x)[2] = (unsigned long)stack_hacked;
> +#else
> +	unsigned long long x = 0;
> +
> +	((unsigned long long *)&x)[2] = (unsigned long)stack_hacked;
> +#endif
> +}
> +#pragma GCC pop_options

This is absolutely atrocious.

The #pragma like Kees already said just need to go. Also, there's
absolutely no clue what so ever what it attempts to achieve.

The __i386__ ifdeffery is horrible crap. Splitting an asm with #ifdef
like that is also horrible crap.

This is not how you write code.

Get asm/asm.h into userspace and then write something like:


void ibt_violation(void)
{
	asm volatile("lea  1f, %" _ASM_AX "\n\t"
		     "jmp  *%" _ASM_AX "\n\t"
		     "1:\n\t" ::: "a");

	WRITE_ONCE(result[test_id], -1);
	WRITE_ONCE(test_id, test_id+1);

	setcontext(&ucp);
}

void shstk_violation(void)
{
	unsigned long x = 0;

	WRITE_ONCE(x[2], stack_hacked);
}