On Mon, Sep 21, 2020 at 02:18:49PM -0700, Sean Christopherson wrote: > On Tue, Sep 22, 2020 at 12:07:36AM +0300, Jarkko Sakkinen wrote: > > On Mon, Sep 21, 2020 at 09:57:58AM -0700, Sean Christopherson wrote: > > > On Mon, Sep 21, 2020 at 03:49:46PM +0300, Jarkko Sakkinen wrote: > > > > On Fri, Sep 18, 2020 at 04:53:37PM -0700, Sean Christopherson wrote: > > > > > a noexec filesystem by loading code into an enclave, and to give the kernel the > > > > > option of adding enclave specific LSM policies in the future. > > > > > > > > > > The source file (if one exists) for the enclave is long gone when the enclave > > > > > is actually mmap()'d and mprotect()'d. To enforce noexec, the requested > > > > > permissions for a given page are snapshotted when the page is added to the > > > > > enclave, i.e. when the enclave is built. Enclave pages that will be executable > > > > > must originate from an a MAYEXEC VMA, e.g. the source page can't come from a > > > > > noexec file system. > > > > > > > > noexec check is done in __sgx_encl_add_page(), not in this callback. > > > > sgx_vma_mprotect() calls sgx_encl_may_map(), which iterates the > > > > addresses, checks that permissions are not surpassed and there are > > > > no holes. > > > > > > Yes, that's what I said. > > > > sgx_encl_add_page() will remove such page. The callback does not > > interact with this process as such pages never get to the enclave. > > I think we're in violent agreement, mostly. > > Userspace can add the page without EXEC permissions in the EPCM, and thus > avoid the noexec/VM_MAYEXEC check. The enclave can then do EMODPE to gain > EXEC permissions in the EPMC. Without the ->mprotect() hook, we wouldn't > be able to detect/prevent such shenanigans. Right, the VM_MAYEXEC in the code is nested under VM_EXEC check. I'm only wondering why not block noexec completely with any permissions, i.e. why not just have unconditional VM_MAYEXEC check? /Jarkko
