Re: [PATCH V3 05/30] x86/sgx: Support loading enclave page without VMA permissions check

[Jarkko Sakkinen <jarkko@kernel.org>]

On Mon, Apr 04, 2022 at 09:49:13AM -0700, Reinette Chatre wrote:
> sgx_encl_load_page() is used to find and load an enclave page into
> enclave (EPC) memory, potentially loading it from the backing storage.
> Both usages of sgx_encl_load_page() are during an access to the
> enclave page from a VMA and thus the permissions of the VMA are
> considered before the enclave page is loaded.
> 
> SGX2 functions operating on enclave pages belonging to an initialized
> enclave requiring the page to be in EPC. It is thus required to
> support loading enclave pages into the EPC independent from a VMA.
> 
> Split the current sgx_encl_load_page() to support the two usages:
> A new call, sgx_encl_load_page_in_vma(), behaves exactly like the
> current sgx_encl_load_page() that takes VMA permissions into account,
> while sgx_encl_load_page() just loads an enclave page into EPC.
> 
> VMA, PTE, and EPCM permissions would continue to dictate whether
> the pages can be accessed from within an enclave.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
> Changes since V2:
> - New patch
> 
>  arch/x86/kernel/cpu/sgx/encl.c | 57 ++++++++++++++++++++++------------
>  arch/x86/kernel/cpu/sgx/encl.h |  2 ++
>  2 files changed, 40 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 7c63a1911fae..05ae1168391c 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -131,25 +131,10 @@ static struct sgx_epc_page *sgx_encl_eldu(struct sgx_encl_page *encl_page,
>  	return epc_page;
>  }
>  
> -static struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
> -						unsigned long addr,
> -						unsigned long vm_flags)
> +static struct sgx_encl_page *__sgx_encl_load_page(struct sgx_encl *encl,
> +						  struct sgx_encl_page *entry)
>  {
> -	unsigned long vm_prot_bits = vm_flags & (VM_READ | VM_WRITE | VM_EXEC);
>  	struct sgx_epc_page *epc_page;
> -	struct sgx_encl_page *entry;
> -
> -	entry = xa_load(&encl->page_array, PFN_DOWN(addr));
> -	if (!entry)
> -		return ERR_PTR(-EFAULT);
> -
> -	/*
> -	 * Verify that the faulted page has equal or higher build time
> -	 * permissions than the VMA permissions (i.e. the subset of {VM_READ,
> -	 * VM_WRITE, VM_EXECUTE} in vma->vm_flags).
> -	 */
> -	if ((entry->vm_max_prot_bits & vm_prot_bits) != vm_prot_bits)
> -		return ERR_PTR(-EFAULT);
>  
>  	/* Entry successfully located. */
>  	if (entry->epc_page) {
> @@ -175,6 +160,40 @@ static struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
>  	return entry;
>  }
>  
> +static struct sgx_encl_page *sgx_encl_load_page_in_vma(struct sgx_encl *encl,
> +						       unsigned long addr,
> +						       unsigned long vm_flags)
> +{
> +	unsigned long vm_prot_bits = vm_flags & (VM_READ | VM_WRITE | VM_EXEC);
> +	struct sgx_encl_page *entry;
> +
> +	entry = xa_load(&encl->page_array, PFN_DOWN(addr));
> +	if (!entry)
> +		return ERR_PTR(-EFAULT);
> +
> +	/*
> +	 * Verify that the page has equal or higher build time
> +	 * permissions than the VMA permissions (i.e. the subset of {VM_READ,
> +	 * VM_WRITE, VM_EXECUTE} in vma->vm_flags).
> +	 */
> +	if ((entry->vm_max_prot_bits & vm_prot_bits) != vm_prot_bits)
> +		return ERR_PTR(-EFAULT);
> +
> +	return __sgx_encl_load_page(encl, entry);
> +}
> +
> +struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
> +					 unsigned long addr)
> +{
> +	struct sgx_encl_page *entry;
> +
> +	entry = xa_load(&encl->page_array, PFN_DOWN(addr));
> +	if (!entry)
> +		return ERR_PTR(-EFAULT);
> +
> +	return __sgx_encl_load_page(encl, entry);
> +}
> +
>  static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
>  {
>  	unsigned long addr = (unsigned long)vmf->address;
> @@ -196,7 +215,7 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
>  
>  	mutex_lock(&encl->lock);
>  
> -	entry = sgx_encl_load_page(encl, addr, vma->vm_flags);
> +	entry = sgx_encl_load_page_in_vma(encl, addr, vma->vm_flags);
>  	if (IS_ERR(entry)) {
>  		mutex_unlock(&encl->lock);
>  
> @@ -344,7 +363,7 @@ static struct sgx_encl_page *sgx_encl_reserve_page(struct sgx_encl *encl,
>  	for ( ; ; ) {
>  		mutex_lock(&encl->lock);
>  
> -		entry = sgx_encl_load_page(encl, addr, vm_flags);
> +		entry = sgx_encl_load_page_in_vma(encl, addr, vm_flags);
>  		if (PTR_ERR(entry) != -EBUSY)
>  			break;
>  
> diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
> index fec43ca65065..6b34efba1602 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -116,5 +116,7 @@ unsigned int sgx_alloc_va_slot(struct sgx_va_page *va_page);
>  void sgx_free_va_slot(struct sgx_va_page *va_page, unsigned int offset);
>  bool sgx_va_page_full(struct sgx_va_page *va_page);
>  void sgx_encl_free_epc_page(struct sgx_epc_page *page);
> +struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
> +					 unsigned long addr);
>  
>  #endif /* _X86_ENCL_H */
> -- 
> 2.25.1
> 


Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko