Re: [PATCH v16 18/22] platform/x86: Intel SGX driver

[Sean Christopherson]

On Tue, 2018-11-06 at 15:45 +0200, Jarkko Sakkinen wrote:
> Intel Software Guard eXtensions (SGX) is a set of CPU instructions that
> can be used by applications to set aside private regions of code and
> data. The code outside the enclave is disallowed to access the memory
> inside the enclave by the CPU access control.
>Â
> SGX driver provides a ioctl API for loading and initializing enclaves.
> Address range for enclaves is reserved with mmap() and they are
> destroyed with munmap(). Enclave construction, measurement and
> initialization is done with the provided the ioctl API.

...

> +struct sgx_encl {
> +	unsigned int flags;
> +	uint64_t attributes;
> +	uint64_t xfrm;
> +	unsigned int page_cnt;
> +	unsigned int secs_child_cnt;
> +	struct mutex lock;
> +	struct mm_struct *mm;
> +	struct file *backing;

Is there any particular reason why the kernel manages the backing for
the enclave and the PCMDs?ÂÂCould we have userspace provide the backing
either through the ECREATE ioctl() or maybe a completely new ioctl(),
e.g. to give userspace the option to back the enclave with a NVDIMM
instead of RAM? ÂA separate ioctl() with control flags might give us
some flexibility in the future, e.g. maybe there are use cases where
userspace would prefer to kill enclaves rather than swap EPC.

> +	struct kref refcount;
> +	unsigned long base;
> +	unsigned long size;
> +	unsigned long ssaframesize;
> +	struct radix_tree_root page_tree;
> +	struct list_head add_page_reqs;
> +	struct work_struct add_page_work;
> +	struct sgx_encl_page secs;
> +	struct pid *tgid;
> +	struct mmu_notifier mmu_notifier;
> +	struct notifier_block pm_notifier;
> +};