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Date:   Mon, 3 Oct 2022 21:37:06 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Rick Edgecombe <rick.p.edgecombe@intel.com>, x86@kernel.org,
        "H . Peter Anvin" <hpa@zytor.com>,
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        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        "H . J . Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
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Subject: Re: [PATCH v2 29/39] x86/cet/shstk: Support wrss for userspace
Message-ID: <202210032129.44F6E027D@keescook>
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
 <20220929222936.14584-30-rick.p.edgecombe@intel.com>
 <202210031525.78F3FA8@keescook>
 <6ea0841f-5086-9569-028b-922ec01a9196@kernel.org>
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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