linux-kernel - Re: [PATCH v9 23/42] Documentation/x86: Add CET shadow stack description

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Date:   Tue, 13 Jun 2023 12:55:48 +0100
From:   Mark Brown <broonie@...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,
        david@...hat.com, debug@...osinc.com, szabolcs.nagy@....com,
        torvalds@...ux-foundation.org, Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v9 23/42] Documentation/x86: Add CET shadow stack
 description

On Mon, Jun 12, 2023 at 05:10:49PM -0700, Rick Edgecombe wrote:

> +Enabling arch_prctl()'s
> +=======================
> +
> +Elf features should be enabled by the loader using the below arch_prctl's. They
> +are only supported in 64 bit user applications. These operate on the features
> +on a per-thread basis. The enablement status is inherited on clone, so if the
> +feature is enabled on the first thread, it will propagate to all the thread's
> +in an app.

I appreciate it's very late in the development of this series but given
that there are very similar features on both arm64 and riscv would it
make sense to make these just regular prctl()s, arch_prctl() isn't used
on other architectures and it'd reduce the amount of arch specific work
that userspace needs to do if the interface is shared.

It should also be possible to support both interfaces for x86 I guess,
though that feels like askng for trouble.

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