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Date:   Tue, 12 Dec 2023 19:22:24 +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>,
        Florian Weimer <fweimer@redhat.com>,
        Christian Brauner <brauner@kernel.org>,
        Thiago Jung Bauermann <thiago.bauermann@linaro.org>,
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Subject: Re: [PATCH v7 02/39] prctl: arch-agnostic prctl for shadow stack
Message-ID: <d708b493-267a-4418-be91-9bde6b2cf50c@sirena.org.uk>
References: <20231122-arm64-gcs-v7-0-201c483bd775@kernel.org>
 <20231122-arm64-gcs-v7-2-201c483bd775@kernel.org>
 <CAKC1njSC5cC_fXnyNAPt=WU6cD-OjLKFxo90oVPmsLJbuWf4nw@mail.gmail.com>
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On Tue, Dec 12, 2023 at 11:17:11AM -0800, Deepak Gupta wrote:
> On Wed, Nov 22, 2023 at 1:43=E2=80=AFAM Mark Brown <broonie@kernel.org> w=
rote:

> > +/*
> > + * Set the current shadow stack configuration.  Enabling the shadow
> > + * stack will cause a shadow stack to be allocated for the thread.
> > + */
> > +#define PR_SET_SHADOW_STACK_STATUS      72
> > +# define PR_SHADOW_STACK_ENABLE         (1UL << 0)

> Other architecture may require disabling shadow stack if glibc
> tunables is set to permissive mode.
> In permissive mode, if glibc encounters `dlopen` on an object which
> doesn't support shadow stack,
> glibc should be able to issue PR_SHADOW_STACK_DISABLE.

> Architectures can choose to implement or not but I think arch agnostic
> code should enumerate this.

The current implementation for arm64 and therefore API for the prctl()
is that whatever combination of flags is specified will be set, this
means that setting the status to something that does not include _ENABLE
will result in disabling and we don't need a separate flag for disable.
We have use cases that make active use of disabling at runtime.

Please delete unneeded context from replies, it makes it much easier to
find new content.

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