linux-kernel - Re: [PATCH 02/35] prctl: Add flag for shadow stack writeability and push/pop

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Message-ID: <a236d8bb1593035252f7094b6461e4d2c5b432a1.camel@intel.com>
Date:   Tue, 18 Jul 2023 17:47:32 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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        "maz@...nel.org" <maz@...nel.org>,
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Subject: Re: [PATCH 02/35] prctl: Add flag for shadow stack writeability and
 push/pop

On Sun, 2023-07-16 at 22:50 +0100, Mark Brown wrote:
> On arm64 and x86 the kernel can control if there is write access to
> the
> shadow stack via specific instructions defined for the purpose,
> useful
> for things like userspace threading at the expense of some security.
> Add a flag to allow this to be selected when changing the shadow
> stack
> status.
> 
> On arm64 the kernel can separately control if userspace is able to
> pop
> and push values directly onto the shadow stack via GCS push and pop
> instructions, supporting many scenarios where userspace needs to
> write
> to the stack with less security exposure than full write access.  Add
> a
> flag to allow this to be selected when changing the shadow stack
> status.

Is this correct? I thought Szabolcs was saying pop was always
supported, but push was optional.