linux-kernel - Re: [PATCH v2 29/39] x86/cet/shstk: Support wrss for userspace

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Message-ID: <202210032129.44F6E027D@keescook>
Date:   Mon, 3 Oct 2022 21:37:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Rick Edgecombe <rick.p.edgecombe@...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>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        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>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com
Subject: Re: [PATCH v2 29/39] x86/cet/shstk: Support wrss for userspace

On Mon, Oct 03, 2022 at 04:00:36PM -0700, Andy Lutomirski wrote:
> On 10/3/22 15:28, Kees Cook wrote:
> > On Thu, Sep 29, 2022 at 03:29:26PM -0700, Rick Edgecombe wrote:
> > > For the current shadow stack implementation, shadow stacks contents easily
> > > be arbitrarily provisioned with data.
> > 
> > I can't parse this sentence.
> > 
> > > This property helps apps protect
> > > themselves better, but also restricts any potential apps that may want to
> > > do exotic things at the expense of a little security.
> > 
> > Is anything using this right now? Wouldn't thing be safer without WRSS?
> > (Why can't we skip this patch?)
> > 
> 
> So that people don't write programs that need either (shstk off) or (shstk
> on and WRSS on) and crash or otherwise fail on kernels that support shstk
> but don't support WRSS, perhaps?

Right, yes. I meant more "what programs currently need WRSS to operate
under shstk? (And what is it that they are doing that needs it?)"

All is see currently is compiler self-tests and emulators using it?
https://codesearch.debian.net/search?q=%5Cb%28wrss%7CWRSS%29%5Cb&literal=0&perpkg=1

-- 
Kees Cook