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From:   Florian Weimer <fweimer@redhat.com>
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
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Subject: Re: [PATCH 34/35] x86/cet/shstk: Support wrss for userspace
In-Reply-To: <20220130211838.8382-35-rick.p.edgecombe@intel.com> (Rick
        Edgecombe's message of "Sun, 30 Jan 2022 13:18:37 -0800")
References: <20220130211838.8382-1-rick.p.edgecombe@intel.com>
        <20220130211838.8382-35-rick.p.edgecombe@intel.com>
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Date:   Mon, 31 Jan 2022 08:56:45 +0100
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* Rick Edgecombe:

> For the current shadow stack implementation, shadow stacks contents cannot
> be arbitrarily provisioned with data. This property helps apps protect
> themselves better, but also restricts any potential apps that may want to
> do exotic things at the expense of a little security.
>
> The x86 shadow stack feature introduces a new instruction, wrss, which
> can be enabled to write directly to shadow stack permissioned memory from
> userspace. Allow it to get enabled via the prctl interface.

Why can't this be turned on unconditionally?

Thanks,
Florian