linux-kernel - Re: [PATCH v19 24/25] x86/cet/shstk: Add arch

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Message-ID: <202102051026.B250352D4@keescook>
Date:   Fri, 5 Feb 2021 10:26:52 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
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>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v19 24/25] x86/cet/shstk: Add arch_prctl functions for
 shadow stack

On Thu, Feb 04, 2021 at 03:41:59PM -0800, Yu, Yu-cheng wrote:
> On 2/4/2021 12:35 PM, Kees Cook wrote:
> > On Wed, Feb 03, 2021 at 02:55:46PM -0800, Yu-cheng Yu wrote:
> > > arch_prctl(ARCH_X86_CET_STATUS, u64 *args)
> > >      Get CET feature status.
> > > 
> > >      The parameter 'args' is a pointer to a user buffer.  The kernel returns
> > >      the following information:
> > > 
> > >      *args = shadow stack/IBT status
> > >      *(args + 1) = shadow stack base address
> > >      *(args + 2) = shadow stack size
> > 
> > What happens if this needs to grow in the future? Should the first u64
> > contain the array size?
> > 
> > Otherwise, looks sensible.
> > 
> > -Kees
> > 
> 
> The first item is a bitmap, and there are two possible bits.  Should there
> be a need, we can then do things about it.  My thought at the moment is, we
> may not meet the situation.  Can we keep this for now?

Ah, good point. Yes, since that's a bitmap it ends up describing what
follows. This is fine as-is. Thanks!

Reviewed-by: Kees Cook <keescook@...omium.org>


-- 
Kees Cook