linux-kernel - Re: [PATCH v4 33/39] x86: Prevent 32 bit operations for 64 bit shstk tasks

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Message-ID: <CALCETrVMY4UadSrn3fTim5iCzPVf+XXnkyq57wjvnhVUNV1V5w@mail.gmail.com>
Date:   Sat, 3 Dec 2022 14:49:34 -0800
From:   Andy Lutomirski <luto@...nel.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>,
        Kees Cook <keescook@...omium.org>,
        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
Subject: Re: [PATCH v4 33/39] x86: Prevent 32 bit operations for 64 bit shstk tasks

On Fri, Dec 2, 2022 at 4:44 PM Rick Edgecombe
<rick.p.edgecombe@...el.com> wrote:
>

> So since 32 bit is not easy to support, and there are likely not many
> users. More cleanly don't support 32 bit signals in a 64 bit address
> space by not allowing 32 bit ABI signal handlers when shadow stack is
> enabled. Do this by clearing any 32 bit ABI signal handlers when shadow
> stack is enabled, and disallow any further 32 bit ABI signal handlers.
> Also, return an error code for the clone operations when in a 32 bit
> syscall.
>

This seems unfortunate.  The result will be a highly incomprehensible
crash.  Maybe instead deny enabling shadow stack in the first place?
Or at least pr_warn_once if anything gets flushed.