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

Peter Zijlstra
2020-05-22T09:36:46Z

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);
}