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

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Date:   Tue, 13 Jun 2023 16:15:31 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Florian Weimer <fweimer@...hat.com>
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>,
        "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 Tue, Jun 13, 2023 at 02:37:18PM +0200, Florian Weimer wrote:

> > 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.

> Has the Arm feature been fully disclosed?

Unfortunately no, it's not yet been folded into the ARM.  The system
registers and instructions are in the latest XML releases but that's not
the full story.

> I would expect the integration with stack switching and unwinding
> differs between architectures even if the core mechanism is similar.
> It's probably tempting to handle shadow stack placement differently,
> too.

Yeah, there's likely to be some differences (though given the amount of
discussion on the x86 implementation I'm trying to follow the decisions
there as much as reasonable on the basis that we should hopefully come
to the same conclusions).  It seemed worth mentioning as a needless
bump, OTOH I defninitely don't see it as critical.

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