linux-kernel - Re: [RFC PATCH v2 18/27] x86/cet/shstk: Introduce WRUSS instruction

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <55A0592D-0E8D-4BC5-BA4B-E82E92EEA36A@amacapital.net>
Date:   Thu, 12 Jul 2018 19:21:42 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>, 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>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omiun.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>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v2 18/27] x86/cet/shstk: Introduce WRUSS instruction



> On Jul 12, 2018, at 6:50 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> 
> On 07/12/2018 04:49 PM, Dave Hansen wrote:
>>>> That seems like something we need to call out if so.  It also means we
>>>> need to update the SDM because some of the text is wrong.
>>> It needs to mention the WRUSS case.
>> Ugh.  The documentation for this is not pretty.  But, I guess this is
>> not fundamentally different from access to U=1 pages when SMAP is in
>> place and we've set EFLAGS.AC=1.
> 
> I was wrong and misread the docs.  We do not get X86_PF_USER set when
> EFLAGS.AC=1.
> 
> But, we *do* get X86_PF_USER (otherwise defined to be set when in ring3)
> when running in ring0 with the WRUSS instruction and some other various
> shadow-stack-access-related things.  I'm sure folks had a good reason
> for this architecture, but it is a pretty fundamentally *new*
> architecture that we have to account for.

I think it makes (some) sense. The USER bit is set for a page fault that was done with user privilege. So a descriptor table fault at CPL 3 has USER clear (regardless of the cause of the fault) and WRUSS has USER set.

> 
> This new architecture is also not spelled out or accounted for in the
> SDM as of yet.  It's only called out here as far as I know:
> https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-enforcement-technology-preview.pdf
> 
> Which reminds me:  Yu-cheng, do you have a link to the docs anywhere in
> your set?  If not, you really should.

I am tempted to suggest that the whole series not be merged until there are actual docs. It’s not a fantastic precedent.