linux-kernel - Re: [PATCH v27 24/31] x86/cet/shstk: Handle thread shadow stack

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Message-ID: <ee98275e-cd1d-ad94-73cd-470bf89ca344@intel.com>
Date:   Wed, 21 Jul 2021 11:34:53 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Florian Weimer <fweimer@...hat.com>,
        John Allen <john.allen@....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>,
        "H.J. Lu" <hjl.tools@...il.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>,
        Dave Martin <Dave.Martin@....com>,
        "Weijiang Yang" <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        "Haitao Huang" <haitao.huang@...el.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH v27 24/31] x86/cet/shstk: Handle thread shadow stack

On 7/21/2021 11:28 AM, Florian Weimer wrote:
> * John Allen:
> 
>> At the very least, it would seem that on some systems, it isn't valid to
>> rely on the stack_size passed from clone3, though I'm unsure what the
>> correct behavior should be here. If the passed stack_size == 0 and sp ==
>> 0, is this a case where we want to alloc a shadow stack for this thread
>> with some capped size? Alternatively, is this a case that isn't valid to
>> alloc a shadow stack and we should simply return 0 instead of -EINVAL?
>>
>> I'm running Fedora 34 which satisfies the required versions of gcc,
>> binutils, and glibc.
> 
> Fedora 34 doesn't use clone3 yet.  You can upgrade to a rawhide build,
> e.g. glibc-2.33.9000-46.fc35:
> 
>    <https://koji.fedoraproject.org/koji/buildinfo?buildID=1782678>
> 
> It's currently not in main rawhide because the Firefox sandbox breaks
> clone3.  The “fix” is that clone3 will fail with ENOSYS under the
> sandbox.
> 
> I expect that container runtimes turn clone3 into clone in the same way
> (via ENOSYS), at least for the medium term.  So it would make sense to
> allocate some sort of shadow stack for clone as well, if that's possible
> to implement in some way.
> 
> Thanks,
> Florian
> 

Thanks Florian!  And because of that reason, we will put back clone2 
support in my next v28 patches.

Yu-cheng