linux-kernel - Re: [PATCH v7 02/39] prctl: arch-agnostic prctl for shadow stack

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Message-ID: <feb6d1fc-c144-4f2b-833f-b3e00646cf30@sirena.org.uk>
Date:   Wed, 13 Dec 2023 19:48:28 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Deepak Gupta <debug@...osinc.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Arnd Bergmann <arnd@...db.de>, Oleg Nesterov <oleg@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Florian Weimer <fweimer@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Thiago Jung Bauermann <thiago.bauermann@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v7 02/39] prctl: arch-agnostic prctl for shadow stack

On Wed, Dec 13, 2023 at 11:43:49AM -0800, Deepak Gupta wrote:
> On Wed, Dec 13, 2023 at 5:37 AM Mark Brown <broonie@...nel.org> wrote:
> > On Tue, Dec 12, 2023 at 04:50:38PM -0800, Deepak Gupta wrote:

> > > How will it do that (currently _ENABLE is married to _WRITE and _PUSH) ?

> > That's feeling moderately firmly into "don't do that" territory to be
> > honest, the problems of trying to modify the stack of another running
> > thread while it's active just don't seem worth it - if you're
> > coordinating enough to do the modifications it's probably possible to
> > just ask the thread who's stack is being modified to do the modification
> > itself and having an unprotected thread writing into shadow stack memory
> > doesn't feel great.

> Yeah no leanings on my side. Just wanted to articulate this scenario.
> Since this is new ground,
> we can define what's appropriate. Let's keep it this way where a
> thread can write to shadow
> stack mappings only when it itself has shadow stack enabled.

Sounds good to me - it's much easier to relax permissions later than to
tighten them up.

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