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

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]

Date:   Wed, 5 Oct 2022 20:11:58 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "Lutomirski, Andy" <luto@...nel.org>,
        "bsingharora@...il.com" <bsingharora@...il.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Syromiatnikov, Eugene" <esyr@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Eranian, Stephane" <eranian@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "nadav.amit@...il.com" <nadav.amit@...il.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "dethoma@...rosoft.com" <dethoma@...rosoft.com>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>, "oleg@...hat.com" <oleg@...hat.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "Yang, Weijiang" <weijiang.yang@...el.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "pavel@....cz" <pavel@....cz>, "arnd@...db.de" <arnd@...db.de>,
        "Moreira, Joao" <joao.moreira@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "john.allen@....com" <john.allen@....com>,
        "rppt@...nel.org" <rppt@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "corbet@....net" <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "gorcunov@...il.com" <gorcunov@...il.com>
Subject: Re: [PATCH v2 29/39] x86/cet/shstk: Support wrss for userspace

On Thu, Oct 06, 2022 at 12:38:06AM +0000, Edgecombe, Rick P wrote:
> On Mon, 2022-10-03 at 21:37 -0700, Kees Cook wrote:
> > 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
> 
> Most apps that weren't just automatically compiled haven't had
> implementation effort yet. (of course glibc has had a bunch) I hope we
> would see more of that when we finally get it upstream. So I think a
> better question is, how many apps will need WRSS when they go to enable
> shadow stack. I'm thinking the answer must be some and it could be nice
> to catch them when they first investigate enabling it.
> 
> But yes, except for Mike's CRIU branch, there aren't any programs that
> use it today, and we could drop it for a first implementation. I don't
> see it as something that would only make things less safe though. It
> just lets apps that can't easily work within the stricter shadow stack
> environment, at least get access to a weaker but still beneficial one.
> 
> Kees, did you catch that it can be locked off while enabling shadow
> stack?

Yup, saw that! Looks good. Thanks. :)

-- 
Kees Cook