Re: [PATCH v10 04/40] arm64: Document boot requirements for Guarded Control Stacks

On Thu, Aug 01, 2024 at 01:06:31PM +0100, Mark Brown wrote:

• • If EL2 is present:
• • GCSCR_EL2 must be initialised to 0.
• • If the kernel is entered at EL1 and EL2 is present:
• • GCSCR_EL1 must be initialised to 0.
• • GCSCRE0_EL1 must be initialised to 0.

Currently booting.rst doesn't list *_EL1 registers to be initialised when the kernel is entered at EL1, that would usually be the responsibility of EL1. The exception is some bits in SCTLR_EL1 around not entering with the MMU and caches enabled. But here I think it makes sense to add these GCS registers since if some random bits are set, they can affect kernels (and user apps) that don't have GCS support.

Don't we need HCRX_EL2.GCSEn to be set when entered at EL1?