linux-kernel - Re: [NEEDS-REVIEW] Re: [PATCH v11 25/25] x86/cet/shstk: Add arch

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Message-ID: <439e1e08-58c0-ac91-b073-a471111ad8e2@intel.com>
Date:   Tue, 15 Sep 2020 13:16:41 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Dave Martin <Dave.Martin@....com>, "H.J. Lu" <hjl.tools@...il.com>,
        Florian Weimer <fweimer@...hat.com>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        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>,
        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>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Weijiang Yang <weijiang.yang@...el.com>
Subject: Re: [NEEDS-REVIEW] Re: [PATCH v11 25/25] x86/cet/shstk: Add
 arch_prctl functions for shadow stack

On 9/15/2020 12:24 PM, Dave Hansen wrote:
> On 9/15/20 12:08 PM, Yu-cheng Yu wrote:
>> On Mon, 2020-09-14 at 17:12 -0700, Yu, Yu-cheng wrote:
>>> On 9/14/2020 7:50 AM, Dave Hansen wrote:
>>>> On 9/11/20 3:59 PM, Yu-cheng Yu wrote:
>>>> ...
>>>>> Here are the changes if we take the mprotect(PROT_SHSTK) approach.
>>>>> Any comments/suggestions?
>>>> I still don't like it. :)
>>>>
>>>> I'll also be much happier when there's a proper changelog to accompany
>>>> this which also spells out the alternatives any why they suck so much.
>> [...]
>>
>> I revised it.  If this turns out needing more work/discussion, we can split it
>> out from the shadow stack series.
> 
> Where does that leave things?  You only get shadow stacks for
> single-threaded apps which have the ELF bits set?
> 

As long as the system supports shadow stack, any application can 
mmap()/mprotect() a shadow stack.  A pthread can allocate a shadow stack 
too.  However, only shadow stack-enabled programs can activate/use the 
shadow stack.