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

Yu-cheng Yu
2020-05-22T15:10:11Z

On Fri, 2020-05-22 at 11:28 +0200, Peter Zijlstra wrote:
> 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);
> }

Thanks! I will change it.

Yu-cheng