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

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Date:   Fri, 22 May 2020 08:10:14 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>
Subject: Re: [RFC PATCH 5/5] selftest/x86: Add CET quick test

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