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

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Date:   Tue, 06 Nov 2018 08:40:00 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org, linux-sgx@...r.kernel.org
Cc:     dave.hansen@...el.com, nhorman@...hat.com, npmccallum@...hat.com,
        serge.ayoun@...el.com, shay.katz-zamir@...el.com,
        haitao.huang@...el.com, andriy.shevchenko@...ux.intel.com,
        tglx@...utronix.de, kai.svahn@...el.com,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v16 18/22] platform/x86: Intel SGX driver

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.
> 
> 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?  Could 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?  A 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;
> +};