linux-kernel - Re: [PATCH v10 26/26] x86/cet/shstk: Add arch

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Message-ID: <c9c9314374c7db0bf9b6e39670855afe5b0d4014.camel@intel.com>
Date:   Fri, 22 May 2020 10:17:43 -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: [PATCH v10 26/26] x86/cet/shstk: Add arch_prctl functions for
 shadow stack

On Thu, 2020-05-21 at 15:42 -0700, Kees Cook wrote:
> On Wed, Apr 29, 2020 at 03:07:32PM -0700, Yu-cheng Yu wrote:
[...]
> > +
> > +int prctl_cet(int option, u64 arg2)
> > +{
> > +	struct cet_status *cet;
> > +
> > +	if (!IS_ENABLED(CONFIG_X86_INTEL_CET))
> > +		return -EINVAL;
> 
> Using -EINVAL here means userspace can't tell the difference between an
> old kernel and a kernel not built with CONFIG_X86_INTEL_CET. Perhaps
> -ENOTSUPP?

Looked into this.  The kernel and GLIBC are not in sync.  So maybe we still use
EINVAL here?

Yu-cheng



In kernel:
----------

#define EOPNOTSUPP	95
#define ENOTSUPP 	524

In GLIBC:
---------

printf("ENOTSUP=%d\n", ENOTSUP);
printf("EOPNOTSUPP=%d\n", EOPNOTSUPP);
printf("%s=524\n", strerror(524));
 
ENOTSUP=95
EOPNOTSUPP=95
Unknown error 524=524