Re: [PATCH v40 11/24] x86/sgx: Add SGX misc driver interface

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Nov 05, 2020 at 03:10:54AM +0200, Jarkko Sakkinen wrote:
> Noticed couple of minor glitches.
> 
> On Wed, Nov 04, 2020 at 04:54:17PM +0200, Jarkko Sakkinen wrote:
> > +int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start,
> > +		     unsigned long end, unsigned long vm_flags)
> > +{
> > +	unsigned long vm_prot_bits = vm_flags & (VM_READ | VM_WRITE | VM_EXEC);
> > +	struct sgx_encl_page *page;
> > +	unsigned long count = 0;
> > +	int ret = 0;
> > +
> > +	XA_STATE(xas, &encl->page_array, PFN_DOWN(start));
> > +
> > +	/*
> > +	 * Disallow READ_IMPLIES_EXEC tasks as their VMA permissions might
> > +	 * conflict with the enclave page permissions.
> > +	 */
> > +	if (current->personality & READ_IMPLIES_EXEC)
> > +		return -EACCES;
> > +
> > +	mutex_lock(&encl->lock);
> > +	xas_lock(&xas);
> > +	xas_for_each(&xas, page, PFN_DOWN(end - 1)) {
> > +		if (!page)
> > +			break;
> 
> A redundant check, can be removed.
> 
> > +
> > +		if (~page->vm_max_prot_bits & vm_prot_bits) {
> > +			ret = -EACCES;
> > +			break;
> > +		}
> > +
> > +		/* Reschedule on every XA_CHECK_SCHED iteration. */
> > +		if (!(++count % XA_CHECK_SCHED)) {
> > +			xas_pause(&xas);
> > +			xas_unlock(&xas);
> > +			mutex_unlock(&encl->lock);
> > +
> > +			cond_resched();
> > +
> > +			mutex_lock(&encl->lock);
> > +			xas_lock(&xas);
> > +		}
> > +	}
> > +	xas_unlock(&xas);
> > +	mutex_unlock(&encl->lock);
> > +
> > +	return ret;
> > +}
> > +
> > +static int sgx_vma_mprotect(struct vm_area_struct *vma,
> > +			    struct vm_area_struct **pprev, unsigned long start,
> > +			    unsigned long end, unsigned long newflags)
> > +{
> > +	int ret;
> > +
> > +	ret = sgx_encl_may_map(vma->vm_private_data, start, end, newflags);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return mprotect_fixup(vma, pprev, start, end, newflags);
> > +}
> > +
> > +const struct vm_operations_struct sgx_vm_ops = {
> > +	.fault = sgx_vma_fault,
> > +	.mprotect = sgx_vma_mprotect,
> > +};
> > +
> > +/**
> > + * sgx_encl_find - find an enclave
> > + * @mm:		mm struct of the current process
> > + * @addr:	address in the ELRANGE
> > + * @vma:	the resulting VMA
> > + *
> > + * Find an enclave identified by the given address. Give back a VMA that is
> > + * part of the enclave and located in that address. The VMA is given back if it
> > + * is a proper enclave VMA even if an &sgx_encl instance does not exist yet
> > + * (enclave creation has not been performed).
> > + *
> > + * Return:
> > + *   0 on success,
> > + *   -EINVAL if an enclave was not found,
> > + *   -ENOENT if the enclave has not been created yet
> > + */
> > +int sgx_encl_find(struct mm_struct *mm, unsigned long addr,
> > +		  struct vm_area_struct **vma)
> > +{
> > +	struct vm_area_struct *result;
> > +	struct sgx_encl *encl;
> > +
> > +	result = find_vma(mm, addr);
> > +	if (!result || result->vm_ops != &sgx_vm_ops || addr < result->vm_start)
> > +		return -EINVAL;
> > +
> > +	encl = result->vm_private_data;
> > +	*vma = result;
> > +
> > +	return encl ? 0 : -ENOENT;
> > +}
> 
> Since v20 there has been 1:1 assocition between enclaves and files.
> In other words, this can never return -ENOENT.
> 
> With this reduction the function turns into:
> 
> int sgx_encl_find(struct mm_struct *mm, unsigned long addr,
> 		  struct vm_area_struct **vma)
> {
> 	struct vm_area_struct *result;
> 
> 	result = find_vma(mm, addr);
> 	if (!result || result->vm_ops != &sgx_vm_ops || addr < result->vm_start)
> 		return -EINVAL;
> 
> 	*vma = result;
> 
> 	return 0;
> }
> 
> There are only two call sites:
> 
> 1. sgx_encl_test_and_clear_young()
> 2. sgx_reclaimer_block()
> 
> I.e. would not be a big trouble to tune the signature a bit:
> 
> struct vm_area_struct *sgx_encl_find_vma(struct mm_struct *mm, unsigned long addr)
> {
> 	struct vm_area_struct *result;
> 
> 	result = find_vma(mm, addr);
> 	if (!result || result->vm_ops != &sgx_vm_ops || addr < result->vm_start)
> 		return NULL;
> 
> 	return result;
> }

Further, I'd declare this as an inline function given how trivial it
turn into.

> There is a function called sgx_encl_find_mm(), which is *unrelated* to
> this function and has only one call sites. Its flow is very linear. In
> order to avoid confusion, I'd open code that into sgx_encl_mm_add().
> 
> /Jarkko

/Jarkko