Re: [PATCH] x86/sgx: Do not limit EAUG'd pages by pre-initialization policy

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Mar 04, 2022 at 03:16:35AM +0200, Jarkko Sakkinen wrote:
> Pre-initialization policy is meant for EADD'd pages because they are
> part of the enclave identity. It's a good practice to not let touch the
> permissions after initialization, and does provide guarantees to e.g.
> LSM's about the enclave.
> 
> For EAUG'd pages it should be sufficient to let mmap(), mprotect() and
> SGX opcodes to control the permissions. Thus effectively disable
> pre-initialization policy by setting vm_max_prot_bit and
> vm_run_prot_bits to RWX.
> 
> Cc: Reinette Chatre <reinette.chatre@intel.com>
> Cc: Nathaniel McCallum <nathaniel@profian.com>
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
>  arch/x86/kernel/cpu/sgx/encl.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 5fe7189eac9d..17feb6fa5578 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -200,13 +200,7 @@ static vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
>  	encl_page->desc = addr;
>  	encl_page->encl = encl;
>  
> -	/*
> -	 * Adding a regular page that is architecturally allowed to only
> -	 * be created with RW permissions.
> -	 * TBD: Interface with user space policy to support max permissions
> -	 * of RWX.
> -	 */
> -	prot = PROT_READ | PROT_WRITE;
> +	prot = PROT_READ | PROT_WRITE | PROT_EXEC;
>  	encl_page->vm_run_prot_bits = calc_vm_prot_bits(prot, 0);
>  	encl_page->vm_max_prot_bits = encl_page->vm_run_prot_bits;
>  
> -- 
> 2.35.1
> 

This does not break any existing ABI and at least makes the current
patch set usable.

BR, Jarkko