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SubjectRe: [PATCH v38 13/24] x86/sgx: Add SGX_IOC_ENCLAVE_ADD_PAGES
On Thu, Sep 17, 2020 at 12:34:18AM -0500, Haitao Huang wrote:
> On Tue, 15 Sep 2020 06:05:11 -0500, Jarkko Sakkinen
> <jarkko.sakkinen@linux.intel.com> wrote:
> ...
>
> > +static int __sgx_encl_add_page(struct sgx_encl *encl,
> > + struct sgx_encl_page *encl_page,
> > + struct sgx_epc_page *epc_page,
> > + struct sgx_secinfo *secinfo, unsigned long src)
> > +{
> > + struct sgx_pageinfo pginfo;
> > + struct vm_area_struct *vma;
> > + struct page *src_page;
> > + int ret;
> > +
> > + /* Query vma's VM_MAYEXEC as an indirect path_noexec() check. */
> > + if (encl_page->vm_max_prot_bits & VM_EXEC) {
> > + vma = find_vma(current->mm, src);
> > + if (!vma)
> > + return -EFAULT;
> > +
> > + if (!(vma->vm_flags & VM_MAYEXEC))
> > + return -EACCES;
> > + }
> > +
> > + ret = get_user_pages(src, 1, 0, &src_page, NULL);
> > + if (ret < 1)
> > + return ret;
> > +
> > + pginfo.secs = (unsigned long)sgx_get_epc_addr(encl->secs.epc_page);
> > + pginfo.addr = SGX_ENCL_PAGE_ADDR(encl_page);
> > + pginfo.metadata = (unsigned long)secinfo;
> > + pginfo.contents = (unsigned long)kmap_atomic(src_page);
> > +
> > + ret = __eadd(&pginfo, sgx_get_epc_addr(epc_page));
> > +
> > + kunmap_atomic((void *)pginfo.contents);
> > + put_page(src_page);
> > +
> > + return ret ? -EIO : 0;
> > +}
> > +
> > +/*
> > + * If the caller requires measurement of the page as a proof for the
> > content,
> > + * use EEXTEND to add a measurement for 256 bytes of the page. Repeat
> > this
> > + * operation until the entire page is measured."
> > + */
> > +static int __sgx_encl_extend(struct sgx_encl *encl,
> > + struct sgx_epc_page *epc_page)
> > +{
> > + int ret;
> > + int i;
> > +
> > + for (i = 0; i < 16; i++) {
> > + ret = __eextend(sgx_get_epc_addr(encl->secs.epc_page),
> > + sgx_get_epc_addr(epc_page) + (i * 0x100));
> > + if (ret) {
> > + if (encls_failed(ret))
> > + ENCLS_WARN(ret, "EEXTEND");
> > + return -EIO;
> > + }
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long src,
> > + unsigned long offset, struct sgx_secinfo *secinfo,
> > + unsigned long flags)
> > +{
> > + struct sgx_encl_page *encl_page;
> > + struct sgx_epc_page *epc_page;
> > + int ret;
> > +
> > + encl_page = sgx_encl_page_alloc(encl, offset, secinfo->flags);
> > + if (IS_ERR(encl_page))
> > + return PTR_ERR(encl_page);
> > +
> > + epc_page = __sgx_alloc_epc_page();
> > + if (IS_ERR(epc_page)) {
> > + kfree(encl_page);
> > + return PTR_ERR(epc_page);
> > + }
> > +
> > + mmap_read_lock(current->mm);
> > + mutex_lock(&encl->lock);
> > +
> > + /*
> > + * Insert prior to EADD in case of OOM. EADD modifies MRENCLAVE, i.e.
> > + * can't be gracefully unwound, while failure on EADD/EXTEND is limited
> > + * to userspace errors (or kernel/hardware bugs).
> > + */
> > + ret = xa_insert(&encl->page_array, PFN_DOWN(encl_page->desc),
> > + encl_page, GFP_KERNEL);
> > + if (ret)
> > + goto err_out_unlock;
> > +
> > + ret = __sgx_encl_add_page(encl, encl_page, epc_page, secinfo,
> > + src);
> > + if (ret)
> > + goto err_out;
> > +
> > + /*
> > + * Complete the "add" before doing the "extend" so that the "add"
> > + * isn't in a half-baked state in the extremely unlikely scenario
> > + * the enclave will be destroyed in response to EEXTEND failure.
> > + */
> > + encl_page->encl = encl;
> > + encl_page->epc_page = epc_page;
> > + encl->secs_child_cnt++;
> > +
> > + if (flags & SGX_PAGE_MEASURE) {
> > + ret = __sgx_encl_extend(encl, epc_page);
> > + if (ret)
> > + goto err_out;
> > + }
> > +
> > + mutex_unlock(&encl->lock);
> > + mmap_read_unlock(current->mm);
> > + return ret;
> > +
> > +err_out:
> > + xa_erase(&encl->page_array, PFN_DOWN(encl_page->desc));
> > +
> > +err_out_unlock:
> > + mutex_unlock(&encl->lock);
> > + mmap_read_unlock(current->mm);
> > +
> > + sgx_free_epc_page(epc_page);
> > + kfree(encl_page);
> > +
> > + /*
> > + * Destroy enclave on ENCLS failure as this means that EPC has been
> > + * invalidated.
> > + */
> > + if (ret == -EIO) {
> > + mutex_lock(&encl->lock);
> > + sgx_encl_destroy(encl);
> > + mutex_unlock(&encl->lock);
> > + }
> > +
>
> I think originally we return both count of succeeded EADDs and the errors.
> So we only destroy enclaves in cases of fatal ENCLS failures.
>
> Now we only return errors in all failures other than interrupted operations
> or SGX_MAX_ADD_PAGES_LENGTH is reached.
>
> So, for the new design we should destroy enclaves in all cases here, not
> just for -EIO.
>
> On the other hand, I do like the old way returning both the count and error
> better. It helps greatly for debugging any issues in enclave image or user
> space code, and also keeps flexibility for user space to recover in certain
> errors, such as out of EPC.

Right, I do get the OOM case but wouldn't in that case the reasonable
thing to do destroy the enclave that is not even running? I mean that
means that we are globally out of EPC.

/Jarkko

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