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Date:   Fri, 5 Feb 2021 10:26:52 -0800
From:   Kees Cook <keescook@chromium.org>
To:     "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Cc:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        Pengfei Xu <pengfei.xu@intel.com>
Subject: Re: [PATCH v19 24/25] x86/cet/shstk: Add arch_prctl functions for
 shadow stack
Message-ID: <202102051026.B250352D4@keescook>
References: <20210203225547.32221-1-yu-cheng.yu@intel.com>
 <20210203225547.32221-25-yu-cheng.yu@intel.com>
 <202102041235.BA6C4982F@keescook>
 <6d7dd90f-dc03-06ce-57a2-57e4c2f803f3@intel.com>
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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@chromium.org>


-- 
Kees Cook