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

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Date:   Thu, 21 May 2020 16:23:38 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Kees Cook <keescook@...omium.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>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        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 Thu, 2020-05-21 at 16:02 -0700, Kees Cook wrote:
> On Thu, May 21, 2020 at 02:17:20PM -0700, Yu-cheng Yu wrote:
> > Introduce a quick test to verify shadow stack and IBT are working.
> 
> Cool! :)
> 
> I'd love to see either more of a commit log or more comments in the test
> code itself. I had to spend a bit of time trying to understand how the
> test was working. (i.e. using ucontext to "reset", using segv handler to
> catch some of them, etc.) I have not yet figured out why you need to
> send USR1/USR2 for two of them instead of direct calls?

Yes, I will work on it.

[...]

> > +
> > +#pragma GCC push_options
> > +#pragma GCC optimize ("O0")
> 
> Can you avoid compiler-specific pragmas? (Or verify that Clang also
> behaves correctly here?) Maybe it's better to just build the entire file
> with -O0 in the Makefile?

This file is compiled using -O2 in the makefile.  I will see if other ways are
possible.

[...]

> > +
> > +void segv_handler(int signum, siginfo_t *si, void *uc)
> > +{
> 
> Does anything in siginfo_t indicate which kind of failure you're
> detecting? It'd be nice to verify test_id matches the failure mode being
> tested.

Yes, there is an si_code for control-protection fault.
I will fix this.

Agree with your other comments.

Thanks,
Yu-cheng