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Date:   Wed, 13 Dec 2023 19:48:28 +0000
From:   Mark Brown <broonie@kernel.org>
To:     Deepak Gupta <debug@rivosinc.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Arnd Bergmann <arnd@arndb.de>, Oleg Nesterov <oleg@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Shuah Khan <shuah@kernel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
        "H.J. Lu" <hjl.tools@gmail.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
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        Christian Brauner <brauner@kernel.org>,
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Subject: Re: [PATCH v7 02/39] prctl: arch-agnostic prctl for shadow stack
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On Wed, Dec 13, 2023 at 11:43:49AM -0800, Deepak Gupta wrote:
> On Wed, Dec 13, 2023 at 5:37=E2=80=AFAM Mark Brown <broonie@kernel.org> w=
rote:
> > 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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