linux-kernel - Re: [PATCH 03/10] x86/cet: Signal handling for shadow stack

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Message-ID: <22ccde18-6175-fc57-d1a3-06140b419116@linux.intel.com>
Date:   Thu, 7 Jun 2018 13:17:20 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Andy Lutomirski <luto@...capital.net>
Cc:     Florian Weimer <fweimer@...hat.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. J. Lu" <hjl.tools@...il.com>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Oleg Nesterov <oleg@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        mike.kravetz@...cle.com
Subject: Re: [PATCH 03/10] x86/cet: Signal handling for shadow stack

On 06/07/2018 01:12 PM, Yu-cheng Yu wrote:
>>> +int cet_restore_signal(unsigned long ssp)
>>> +{
>>> +       if (!current->thread.cet.shstk_enabled)
>>> +               return 0;
>>> +       return cet_set_shstk_ptr(ssp);
>>> +}
>> This will blow up if the shadow stack enabled state changes in a
>> signal handler.  Maybe we don't care.
> Yes, the task will get a control protection fault.

Sounds like something to add to the very long list of things that are
unwise to do in a signal handler.  Great manpage fodder.