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SubjectRe: [PATCH v13 10/13] x86/sgx: Add sgx_einit() for initializing enclaves
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On Mon, 2018-08-27 at 21:53 +0300, Jarkko Sakkinen wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> Add a function to perform ENCLS(EINIT), which initializes an enclave,
> which can be used by a driver for running enclaves and VMMs.
>
> Writing the LE hash MSRs is extraordinarily expensive, e.g. 3-4x
> slower
> than normal MSRs, so we use a per-cpu cache to track the last known
> value
> of the MSRs to avoid unnecessarily writing the MSRs with the current
> value.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Co-developed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> ---
> arch/x86/include/asm/sgx.h | 2 +
> arch/x86/kernel/cpu/intel_sgx.c | 86
> +++++++++++++++++++++++++++++++--
> 2 files changed, 85 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> index baf30d49b71f..c15c156436be 100644
> --- a/arch/x86/include/asm/sgx.h
> +++ b/arch/x86/include/asm/sgx.h
> @@ -108,6 +108,8 @@ void sgx_free_page(struct sgx_epc_page *page);
> void sgx_page_reclaimable(struct sgx_epc_page *page);
> struct page *sgx_get_backing(struct file *file, pgoff_t index);
> void sgx_put_backing(struct page *backing_page, bool write);
> +int sgx_einit(struct sgx_sigstruct *sigstruct, struct sgx_einittoken
> *token,
> + struct sgx_epc_page *secs_page, u64 lepubkeyhash[4]);
>
> #define ENCLS_FAULT_FLAG 0x40000000UL
> #define ENCLS_FAULT_FLAG_ASM "$0x40000000"
> diff --git a/arch/x86/kernel/cpu/intel_sgx.c
> b/arch/x86/kernel/cpu/intel_sgx.c
> index 1046478a3ab9..fe25e6805680 100644
> --- a/arch/x86/kernel/cpu/intel_sgx.c
> +++ b/arch/x86/kernel/cpu/intel_sgx.c
> @@ -9,6 +9,7 @@
> #include <linux/sched/signal.h>
> #include <linux/shmem_fs.h>
> #include <linux/slab.h>
> +#include <linux/suspend.h>
> #include <asm/sgx.h>
> #include <asm/sgx_pr.h>
>
> @@ -38,6 +39,18 @@ static LIST_HEAD(sgx_active_page_list);
> static DEFINE_SPINLOCK(sgx_active_page_list_lock);
> static struct task_struct *ksgxswapd_tsk;
> static DECLARE_WAIT_QUEUE_HEAD(ksgxswapd_waitq);
> +static struct notifier_block sgx_pm_notifier;
> +static u64 sgx_pm_cnt;
> +
> +/* The cache for the last known values of IA32_SGXLEPUBKEYHASHx MSRs
> for each
> + * CPU. The entries are initialized when they are first used by
> sgx_einit().
> + */
> +struct sgx_lepubkeyhash {
> + u64 msrs[4];
> + u64 pm_cnt;

May I ask why do we need pm_cnt here? In fact why do we need suspend
staff (namely, sgx_pm_cnt above, and related code in this patch) here
in this patch? From the patch commit message I don't see why we need PM
staff here. Please give comment why you need PM staff, or you may
consider to split the PM staff to another patch.

> +};
> +
> +static DEFINE_PER_CPU(struct sgx_lepubkeyhash *,
> sgx_lepubkeyhash_cache);
>
> /**
> * sgx_reclaim_pages - reclaim EPC pages from the consumers
> @@ -328,6 +341,54 @@ void sgx_put_backing(struct page *backing_page,
> bool write)
> }
> EXPORT_SYMBOL_GPL(sgx_put_backing);
>
> +/**
> + * sgx_einit - initialize an enclave
> + * @sigstruct: a pointer to the SIGSTRUCT
> + * @token: a pointer to the EINITTOKEN
> + * @secs_page: a pointer to the SECS EPC page
> + * @lepubkeyhash: the desired value for IA32_SGXLEPUBKEYHASHx
> MSRs
> + *
> + * Try to perform EINIT operation. If the MSRs are writable, they
> are updated
> + * according to @lepubkeyhash.
> + *
> + * Return:
> + * 0 on success,
> + * -errno on failure
> + * SGX error code if EINIT fails
> + */
> +int sgx_einit(struct sgx_sigstruct *sigstruct, struct sgx_einittoken
> *token,
> + struct sgx_epc_page *secs_page, u64 lepubkeyhash[4])
> +{
> + struct sgx_lepubkeyhash __percpu *cache;
> + bool cache_valid;
> + int i, ret;
> +
> + if (!sgx_lc_enabled)
> + return __einit(sigstruct, token,
> sgx_epc_addr(secs_page));
> +
> + cache = per_cpu(sgx_lepubkeyhash_cache, smp_processor_id());
> + if (!cache) {
> + cache = kzalloc(sizeof(struct sgx_lepubkeyhash),
> GFP_KERNEL);
> + if (!cache)
> + return -ENOMEM;
> + }

It seems per-cpu variable is a pointer to struct sgx_lepubkeyhash, and
the actual structure is allocated at the first time the function is
called. May I ask when will it be freed? It seems the free is not in
this patch. Or I am misunderstanding something?

> +
> + cache_valid = cache->pm_cnt == sgx_pm_cnt;
> + cache->pm_cnt = sgx_pm_cnt;
> + preempt_disable();
> + for (i = 0; i < 4; i++) {
> + if (cache_valid && lepubkeyhash[i] == cache-
> >msrs[i])
> + continue;
> +
> + wrmsrl(MSR_IA32_SGXLEPUBKEYHASH0 + i,
> lepubkeyhash[i]);
> + cache->msrs[i] = lepubkeyhash[i];
> + }
> + ret = __einit(sigstruct, token, sgx_epc_addr(secs_page));
> + preempt_enable();
> + return ret;
> +}
> +EXPORT_SYMBOL(sgx_einit);
> +
> static __init int sgx_init_epc_bank(u64 addr, u64 size, unsigned
> long index,
> struct sgx_epc_bank *bank)
> {
> @@ -426,6 +487,15 @@ static __init int sgx_page_cache_init(void)
> return 0;
> }
>
> +static int sgx_pm_notifier_cb(struct notifier_block *nb, unsigned
> long action,
> + void *data)
> +{
> + if (action == PM_SUSPEND_PREPARE || action ==
> PM_HIBERNATION_PREPARE)
> + sgx_pm_cnt++;
> +
> + return NOTIFY_DONE;
> +}
> +
> static __init int sgx_init(void)
> {
> struct task_struct *tsk;
> @@ -452,20 +522,30 @@ static __init int sgx_init(void)
> if (!(fc & FEATURE_CONTROL_SGX_LE_WR))
> pr_info("IA32_SGXLEPUBKEYHASHn MSRs are not
> writable\n");
>
> - ret = sgx_page_cache_init();
> + sgx_pm_notifier.notifier_call = sgx_pm_notifier_cb;
> + ret = register_pm_notifier(&sgx_pm_notifier);
> if (ret)
> return ret;
>
> + ret = sgx_page_cache_init();
> + if (ret)
> + goto out_pm;
> +
> tsk = kthread_run(ksgxswapd, NULL, "ksgxswapd");
> if (IS_ERR(tsk)) {
> - sgx_page_cache_teardown();
> - return PTR_ERR(tsk);
> + ret = PTR_ERR(tsk);
> + goto out_pcache;
> }
> ksgxswapd_tsk = tsk;
>
> sgx_enabled = true;
> sgx_lc_enabled = !!(fc & FEATURE_CONTROL_SGX_LE_WR);
> return 0;
> +out_pcache:
> + sgx_page_cache_teardown();

I don't think this particular 2 lines of code of 'out_pcache' case
should be in this patch?

Thanks,
-Kai

> +out_pm:
> + unregister_pm_notifier(&sgx_pm_notifier);
> + return ret;
> }
>
> arch_initcall(sgx_init);
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