Re: [PATCH v33 11/21] x86/sgx: Linux Enclave Driver

Borislav Petkov
2020-06-27T17:43:53Z

On Thu, Jun 18, 2020 at 01:08:33AM +0300, Jarkko Sakkinen wrote:
> +static int sgx_encl_init(struct sgx_encl *encl, struct sgx_sigstruct *sigstruct,
> + void *token)
> +{
> + u64 mrsigner[4];
> + int ret;
> + int i;
> + int j;
> +
> + /* Check that the required attributes have been authorized. */
> + if (encl->secs_attributes & ~encl->allowed_attributes)
> + return -EACCES;
> +
> + ret = sgx_get_key_hash(sigstruct->modulus, mrsigner);
> + if (ret)
> + return ret;
> +
> + mutex_lock(&encl->lock);
> +
> + if (atomic_read(&encl->flags) & SGX_ENCL_INITIALIZED) {
> + ret = -EFAULT;
> + goto err_out;
> + }

That test should be the first thing this function or its caller does.

> + for (i = 0; i < SGX_EINIT_SLEEP_COUNT; i++) {
> + for (j = 0; j < SGX_EINIT_SPIN_COUNT; j++) {

Ew, what's that double-loop for?

It tries to init an enclave a bunch of times. Why does it need to init
more than once?

> + ret = sgx_einit(sigstruct, token, encl->secs.epc_page,
> + mrsigner);
> + if (ret == SGX_UNMASKED_EVENT)
> + continue;
> + else
> + break;
> + }
> +
> + if (ret != SGX_UNMASKED_EVENT)
> + break;
> +
> + msleep_interruptible(SGX_EINIT_SLEEP_TIME);
> +
> + if (signal_pending(current)) {
> + ret = -ERESTARTSYS;
> + goto err_out;
> + }
> + }
> +
> + if (ret & ENCLS_FAULT_FLAG) {
> + if (encls_failed(ret))
> + ENCLS_WARN(ret, "EINIT");
> +
> + sgx_encl_destroy(encl);
> + ret = -EFAULT;
> + } else if (ret) {
> + pr_debug("EINIT returned %d\n", ret);
> + ret = -EPERM;
> + } else {
> + atomic_or(SGX_ENCL_INITIALIZED, &encl->flags);
> + }
> +
> +err_out:
> + mutex_unlock(&encl->lock);
> + return ret;
> +}
> +
> +/**
> + * sgx_ioc_enclave_init - handler for %SGX_IOC_ENCLAVE_INIT
> + *
> + * @filep: open file to /dev/sgx

@encl: pointer to an enclave instance (via ioctl() file pointer)

> + * @arg: userspace pointer to a struct sgx_enclave_init instance
> + *
> + * Flush any outstanding enqueued EADD operations and perform EINIT. The
> + * Launch Enclave Public Key Hash MSRs are rewritten as necessary to match
> + * the enclave's MRSIGNER, which is caculated from the provided sigstruct.
> + *
> + * Return:
> + * 0 on success,
> + * SGX error code on EINIT failure,
> + * -errno otherwise
> + */
> +static long sgx_ioc_enclave_init(struct sgx_encl *encl, void __user *arg)
> +{
> + struct sgx_sigstruct *sigstruct;
> + struct sgx_enclave_init einit;
> + struct page *initp_page;
> + void *token;
> + int ret;
> +
> + if (!(atomic_read(&encl->flags) & SGX_ENCL_CREATED))

Might just as well check the other flags: doing EINIT on an already
initialized enclave - SGX_ENCL_INITIALIZED - is perhaps a nono or
similarly on a SGX_ENCL_DEAD enclave.

And you could do similar sanity checks in the other ioctl functions.

--
Regards/Gruss,
Boris.