On Mon, Oct 05, 2020 at 08:42:07PM +0300, Jarkko Sakkinen wrote: > On Mon, Oct 05, 2020 at 08:55:19AM -0700, Sean Christopherson wrote: > > On Mon, Oct 05, 2020 at 05:11:19PM +0300, Jarkko Sakkinen wrote: > > > @@ -317,11 +319,30 @@ int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start, > > > if (current->personality & READ_IMPLIES_EXEC) > > > return -EACCES; > > > > > > - xas_for_each(&xas, page, idx_end) > > > - if (!page || (~page->vm_max_prot_bits & vm_prot_bits)) > > > - return -EACCES; > > > + /* > > > + * No need to hold encl->lock: > > > + * 1. None of the page->* get written. > > > + * 2. page->vm_max_prot_bits is set in sgx_encl_page_alloc(). This > > > + * is before calling xa_insert(). After that it is never modified. > > > + */ > > > > You forgot to cover racing with insertion, e.g. below is the snippet from my > > original patch[*], which did the lookup without protection from encl->lock.` > > > > + /* > > + * No need to take encl->lock, vm_prot_bits is set prior to > > + * insertion and never changes, and racing with adding pages is > > + * a userspace bug. > > + */ > > + rcu_read_lock(); > > + page = radix_tree_lookup(&encl->page_tree, idx); > > + rcu_read_unlock(); > > > > > > [*]https://patchwork.kernel.org/patch/11005431/ > > I'm not sure why that was merged as it was but it probably was not > because of that snippet. It had encl->lock before, so it was by all > practical means covered then. I would have replaced encl->lock with that > if I ever had received a patch with just that, i.e. that particular > snippet gone to noise. That's why it was not broken before v36. Or even if that patch was squashed (can't recall that far), it was not intentionally not replaced. I have no idea why encl->lock was not replaced but the code was not broken. /Jarkko
