linux-kernel - Re: [OPTIONAL/RFC v2 37/39] x86/cet: Add PTRACE interface for CET

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Message-ID: <202210041224.E4C63B1@keescook>
Date:   Tue, 4 Oct 2022 12:24:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mike Rapoport <rppt@...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>,
        Andy Lutomirski <luto@...nel.org>,
        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, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [OPTIONAL/RFC v2 37/39] x86/cet: Add PTRACE interface for CET

On Tue, Oct 04, 2022 at 11:44:16AM +0300, Mike Rapoport wrote:
> On Mon, Oct 03, 2022 at 04:59:43PM -0700, Kees Cook wrote:
> > On Thu, Sep 29, 2022 at 03:29:34PM -0700, Rick Edgecombe wrote:
> > > From: Yu-cheng Yu <yu-cheng.yu@...el.com>
> > > 
> > > Some applications (like GDB and CRIU) would like to tweak CET state via
> > 
> > Eee. Does GDB really need this? Can we make this whole thing
> > CONFIG-depend on CRIU?
> 
> GDB, at least its Intel fork uses this. I don't see how they can jump
> between frames without an ability to modify shadow stack contents.
> 
> Last I looked they used NT_X86_CET to update SSP and ptrace(POKEDATA) to
> write to the shadow stack.

Okay, thanks! I appreciate having specific examples. :)

-- 
Kees Cook