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

From: Borislav Petkov <bp@alien8.de>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: x86@kernel.org, linux-sgx@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	Jethro Beekman <jethro@fortanix.com>,
	Haitao Huang <haitao.huang@linux.intel.com>,
	Chunyang Hui <sanqian.hcy@antfin.com>,
	Jordan Hand <jorhand@linux.microsoft.com>,
	Nathaniel McCallum <npmccallum@redhat.com>,
	Seth Moore <sethmo@google.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Suresh Siddha <suresh.b.siddha@intel.com>,
	akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com,
	asapek@google.com, cedric.xing@intel.com,
	chenalexchen@google.com, conradparker@google.com,
	cyhanish@google.com, dave.hansen@intel.com,
	haitao.huang@intel.com, josh@joshtriplett.org,
	kai.huang@intel.com, kai.svahn@intel.com, kmoy@google.com,
	ludloff@google.com, luto@kernel.org, nhorman@redhat.com,
	puiterwijk@redhat.com, rientjes@google.com, tglx@linutronix.de,
	yaozhangx@google.com
Subject: Re: [PATCH v33 11/21] x86/sgx: Linux Enclave Driver
Date: Sat, 27 Jun 2020 19:43:35 +0200
Message-ID: <20200627174335.GC15585@zn.tnic> (raw)
In-Reply-To: <20200617220844.57423-12-jarkko.sakkinen@linux.intel.com>

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.

https://people.kernel.org/tglx/notes-about-netiquette