[PATCH RFC v9 03/25] arm64: mm: Enable overlays for all EL1 indirect permissions

[Linu Cherian]

Kevin,

On Tue, Aug 18, 2026 at 03:08:45PM +0100, Kevin Brodsky wrote:
> In preparation of using POE inside the kernel, enable "Overlay
> applied" for kernel memory types in PIR_EL1. This ensures that the
> permissions set in POR_EL1 affect all kernel mappings.
> 
> User memory types must be left untouched (overlays not applied)
> because any privileged access to user memory (e.g. futex atomic
> without FEAT_LSUI) would then be mistakenly checked against POR_EL1.
> 
> Reviewed-by: David Hildenbrand (Arm) <david at kernel.org>
> Signed-off-by: Kevin Brodsky <kevin.brodsky at arm.com>
> ---
>  arch/arm64/include/asm/pgtable-prot.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index 212ce1b02e15..d4d45ab86a5a 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -183,9 +183,9 @@ static inline bool __pure lpa2_is_enabled(void)
>  	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_SHARED_EXEC),   PIE_RW)     | \
>  	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_READONLY),      PIE_R)      | \
>  	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_SHARED),        PIE_RW)     | \
> -	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_ROX),    PIE_RX)     | \
> -	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_EXEC),   PIE_RWX)    | \
> -	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_RO),     PIE_R)      | \
> -	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL),        PIE_RW))
> +	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_ROX),    PIE_RX_O)   | \
> +	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_EXEC),   PIE_RWX_O)  | \

As part of hardening, should we really add more constraints to the
KERNEL_EXEC by making it PIE_X_O. 

Just trying to undersand, not a concern with the patch as such.

> +	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_RO),     PIE_R_O)    | \
> +	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL),        PIE_RW_O))
>  
>  #endif /* __ASM_PGTABLE_PROT_H */
> 
> -- 
> 2.51.2
>