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

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Message-ID: <6ea0841f-5086-9569-028b-922ec01a9196@kernel.org>
Date:   Mon, 3 Oct 2022 16:00:36 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Kees Cook <keescook@...omium.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.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>,
        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 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?