Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Florian Weimer <fweimer@redhat.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc:     "hjl.tools@gmail.com" <hjl.tools@gmail.com>,
        "bsingharora@gmail.com" <bsingharora@gmail.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "Syromiatnikov, Eugene" <esyr@redhat.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "rdunlap@infradead.org" <rdunlap@infradead.org>,
        "keescook@chromium.org" <keescook@chromium.org>,
        "Yu, Yu-cheng" <yu-cheng.yu@intel.com>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "Eranian, Stephane" <eranian@google.com>,
        "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "nadav.amit@gmail.com" <nadav.amit@gmail.com>,
        "jannh@google.com" <jannh@google.com>,
        "dethoma@microsoft.com" <dethoma@microsoft.com>,
        "kcc@google.com" <kcc@google.com>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "bp@alien8.de" <bp@alien8.de>, "oleg@redhat.com" <oleg@redhat.com>,
        "Yang, Weijiang" <weijiang.yang@intel.com>,
        "Lutomirski, Andy" <luto@kernel.org>,
        "pavel@ucw.cz" <pavel@ucw.cz>, "arnd@arndb.de" <arnd@arndb.de>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mike.kravetz@oracle.com" <mike.kravetz@oracle.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "jamorris@linux.microsoft.com" <jamorris@linux.microsoft.com>,
        "john.allen@amd.com" <john.allen@amd.com>,
        "rppt@kernel.org" <rppt@kernel.org>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>,
        "corbet@lwn.net" <corbet@lwn.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
        "gorcunov@gmail.com" <gorcunov@gmail.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [RFC 37/37] fs/binfmt_elf: Block old shstk elf bit
References: <20221104223604.29615-1-rick.p.edgecombe@intel.com>
        <20221104223604.29615-38-rick.p.edgecombe@intel.com>
        <CAMe9rOpfSccXVWmgK6E0Y0DXC=VX3PpdxXookN1Ty8soeAxrKw@mail.gmail.com>
        <87iljs4ecp.fsf@oldenburg.str.redhat.com>
        <ca106fe1b5005f54525e7a644684108f6a823e14.camel@intel.com>
Date:   Mon, 07 Nov 2022 17:55:54 +0100
In-Reply-To: <ca106fe1b5005f54525e7a644684108f6a823e14.camel@intel.com> (Rick
        P. Edgecombe's message of "Mon, 7 Nov 2022 16:49:58 +0000")
Message-ID: <87h6zaiu05.fsf@oldenburg.str.redhat.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

* Rick P. Edgecombe:

> On Sun, 2022-11-06 at 10:33 +0100, Florian Weimer wrote:
>> * H. J. Lu:
>>=20
>> > This change doesn't make a binary CET compatible.  It just requires
>> > that the toolchain must be updated and all binaries have to be
>> > recompiled with the new toolchain to enable CET.  It doesn't solve
>> > any
>> > issue which can't be solved by not updating glibc.
>>=20
>> Right, and it doesn't even address the library case (the kernel would
>> have to hook into mmap for that).  The kernel shouldn't do this.
>
> Shadow stack shouldn't enable as a result of loading a library, if
> that's what you mean.

It's the opposite=E2=80=94loading incompatible libraries needs to disable s=
hadow
stack (or ideally, not enable it in the first place).  Technically, I
think most incompatible code resides in libraries, so this kernel change
achieves nothing besides punishing early implementations of the
published-as-finalized x86-64 ABI.

Thanks,
Florian