linux-kernel - Re: [PATCH v6 00/41] Shadow stacks for userspace

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Message-ID: <63f2ec1a.a70a0220.bb3e0.bb19@mx.google.com>
Date:   Sun, 19 Feb 2023 19:42:17 -0800
From:   Kees Cook <keescook@...omium.org>
To:     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>,
        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>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Allen <john.allen@....com>, kcc@...gle.com,
        eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, akpm@...ux-foundation.org,
        Andrew.Cooper3@...rix.com, christina.schimpe@...el.com,
        david@...hat.com, debug@...osinc.com
Subject: Re: [PATCH v6 00/41] Shadow stacks for userspace

On Sat, Feb 18, 2023 at 01:13:52PM -0800, Rick Edgecombe wrote:
> This series implements Shadow Stacks for userspace using x86's Control-flow 
> Enforcement Technology (CET). CET consists of two related security features: 
> shadow stacks and indirect branch tracking. This series implements just the 
> shadow stack part of this feature, and just for userspace.

Okay, I've done some bare metal testing, and it all looks happy. The
selftest passes, and I can can see the stack address mismatch get
detected if I explicitly rewrite the saved function pointer on the stack:

[INFO] Want normal flow
[INFO] Found 0x401890 @ 0x7fff47cf2ef8
[INFO] Normal execution flow
[INFO] Want to redirect
[INFO] Found 0x401890 @ 0x7fff47cf2ef8
[INFO] Hijacked execution flow
[INFO] Enabling shadow stack
[INFO] Want to redirect
[INFO] Found 0x401890 @ 0x7fff47cf2ef8
Segmentation fault (core dumped)

Tested-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook