Date:   Thu, 17 Mar 2022 06:12:46 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Cathy Zhang <cathy.zhang@...el.com>
Cc:     linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, ashok.raj@...el.com
Subject: Re: [RFC PATCH v2 01/10] x86/sgx: Introduce mechanism to prevent new
 initializations of EPC pages

On Tue, Mar 15, 2022 at 09:02:51AM +0800, Cathy Zhang wrote:
> == Background ==
> 
> EUPDATESVN is a new SGX instruction which allows enclave attestation
> to include information about updated microcode without a reboot.
> 
> The SGX hardware maintains metadata for each enclave page to help
> enforce its security guarantees. This includes things like a record
> of the enclave to which the page belongs and the type of the page:
> SGX metadata like "VA" or "SECS" pages, or regular enclave pages
> like those that store user data.
> 
> Before an EUPDATESVN operation can be successful, all SGX memory (aka.
> EPC) must be marked as "unused" in the SGX hardware metadata (aka,
> EPCM). The SGX microcode now maintains a reference count of pages
> which are unused to aid in determining when all pages reach the
> "unused" state.
> 
> Both bare-metal and KVM guest EPC must be made unused. To increase
> the chance of a successful EUPDATESVN, the kernel prevents existing
> enclaves from creating new, valid pages and prevents new enclave
> creation (creating an enclave involves initializing a "SECS" page).
> 
> The entire EUPDATESVN process is very slow since it potentially
> affects gigabytes of enclave memory. It can potentially take seconds
> or minutes to complete. Userspace may encounter -EBUSY errors during
> the update and is expected to retry.
> 
> == Patch contents ==
> 
> Introduce mechanism to prevent new initializations of EPC pages.
> 
> Use a flag to indicate when SGX EPC pages are "locked", which means
> it's not allowed to allocate new EPC page for use. Check it in all
> paths that can initialize an EPC page. Use SRCU to ensure that the
> flag is visible across the system before proceeding with an update.
> 
> Add checks to all sites that call SGX instructions that can transition
> pages from unused to initialized to ensure that the SRCU lock is held.
> 
> Signed-off-by: Cathy Zhang <cathy.zhang@...el.com>
> ---
>  arch/x86/kernel/cpu/sgx/encls.h | 10 +++++++
>  arch/x86/kernel/cpu/sgx/sgx.h   |  3 ++
>  arch/x86/kernel/cpu/sgx/encl.c  | 25 +++++++++++++++--
>  arch/x86/kernel/cpu/sgx/ioctl.c | 50 ++++++++++++++++++++++++++++++++-
>  arch/x86/kernel/cpu/sgx/main.c  | 37 ++++++++++++++++++++++++
>  arch/x86/kernel/cpu/sgx/virt.c  | 20 +++++++++++++
>  6 files changed, 142 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
> index 99004b02e2ed..3f1797ec2445 100644
> --- a/arch/x86/kernel/cpu/sgx/encls.h
> +++ b/arch/x86/kernel/cpu/sgx/encls.h
> @@ -139,6 +139,8 @@ static inline bool encls_failed(int ret)
>  /* Initialize an EPC page into an SGX Enclave Control Structure (SECS) page. */
>  static inline int __ecreate(struct sgx_pageinfo *pginfo, void *secs)
>  {
> +	lockdep_assert_held(&sgx_lock_epc_srcu);
> +
>  	return __encls_2(ECREATE, pginfo, secs);
>  }
>  
> @@ -154,6 +156,8 @@ static inline int __eextend(void *secs, void *addr)
>   */
>  static inline int __eadd(struct sgx_pageinfo *pginfo, void *addr)
>  {
> +	lockdep_assert_held(&sgx_lock_epc_srcu);
> +
>  	return __encls_2(EADD, pginfo, addr);
>  }
>  
> @@ -191,6 +195,8 @@ static inline int __etrack(void *addr)
>  static inline int __eldu(struct sgx_pageinfo *pginfo, void *addr,
>  			 void *va)
>  {
> +	lockdep_assert_held(&sgx_lock_epc_srcu);
> +
>  	return __encls_ret_3(ELDU, pginfo, addr, va);
>  }
>  
> @@ -205,6 +211,8 @@ static inline int __epa(void *addr)
>  {
>  	unsigned long rbx = SGX_PAGE_TYPE_VA;
>  
> +	lockdep_assert_held(&sgx_lock_epc_srcu);
> +
>  	return __encls_2(EPA, rbx, addr);
>  }
>  
> @@ -230,6 +238,8 @@ static inline int __emodt(struct sgx_secinfo *secinfo, void *addr)
>  /* Zero a page of EPC memory and add it to an initialized enclave. */
>  static inline int __eaug(struct sgx_pageinfo *pginfo, void *addr)
>  {
> +	lockdep_assert_held(&sgx_lock_epc_srcu);
> +
>  	return __encls_2(EAUG, pginfo, addr);
>  }
>  
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 85cbf103b0dd..dc8cb58100e3 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -104,4 +104,7 @@ static inline int __init sgx_vepc_init(void)
>  
>  void sgx_update_lepubkeyhash(u64 *lepubkeyhash);
>  
> +extern struct srcu_struct sgx_lock_epc_srcu;
> +bool sgx_epc_is_locked(void);
> +
>  #endif /* _X86_SGX_H */
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index a0255d41e075..d2b428992910 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -264,6 +264,7 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
>  	unsigned long phys_addr;
>  	struct sgx_encl *encl;
>  	vm_fault_t ret;
> +	int srcu_idx;
>  
>  	encl = vma->vm_private_data;
>  
> @@ -275,6 +276,12 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
>  	if (unlikely(!encl))
>  		return VM_FAULT_SIGBUS;
>  
> +	srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +	if (sgx_epc_is_locked()) {
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +		return VM_FAULT_SIGBUS;
> +	}
> +
>  	/*
>  	 * The page_array keeps track of all enclave pages, whether they
>  	 * are swapped out or not. If there is no entry for this page and
> @@ -283,14 +290,18 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
>  	 * enclave that will be checked for right away.
>  	 */
>  	if (cpu_feature_enabled(X86_FEATURE_SGX2) &&
> -	    (!xa_load(&encl->page_array, PFN_DOWN(addr))))
> -		return sgx_encl_eaug_page(vma, encl, addr);
> +	    (!xa_load(&encl->page_array, PFN_DOWN(addr)))) {
> +		ret = sgx_encl_eaug_page(vma, encl, addr);
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +		return ret;
> +	}
>  
>  	mutex_lock(&encl->lock);
>  
>  	entry = sgx_encl_load_page(encl, addr);
>  	if (IS_ERR(entry)) {
>  		mutex_unlock(&encl->lock);
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  
>  		if (PTR_ERR(entry) == -EBUSY)
>  			return VM_FAULT_NOPAGE;
> @@ -315,12 +326,14 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
>  				  vm_get_page_prot(page_prot_bits));
>  	if (ret != VM_FAULT_NOPAGE) {
>  		mutex_unlock(&encl->lock);
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  
>  		return VM_FAULT_SIGBUS;
>  	}
>  
>  	sgx_encl_test_and_clear_young(vma->vm_mm, entry);
>  	mutex_unlock(&encl->lock);
> +	srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  
>  	return VM_FAULT_NOPAGE;
>  }
> @@ -513,6 +526,7 @@ static int sgx_vma_access(struct vm_area_struct *vma, unsigned long addr,
>  	struct sgx_encl_page *entry = NULL;
>  	char data[sizeof(unsigned long)];
>  	unsigned long align;
> +	int srcu_idx;
>  	int offset;
>  	int cnt;
>  	int ret = 0;
> @@ -529,6 +543,12 @@ static int sgx_vma_access(struct vm_area_struct *vma, unsigned long addr,
>  		return -EFAULT;
>  
>  	for (i = 0; i < len; i += cnt) {
> +		srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +		if (sgx_epc_is_locked()) {
> +			ret = -EBUSY;
> +			goto out;
> +		}
> +
>  		entry = sgx_encl_reserve_page(encl, (addr + i) & PAGE_MASK);
>  		if (IS_ERR(entry)) {
>  			ret = PTR_ERR(entry);
> @@ -555,6 +575,7 @@ static int sgx_vma_access(struct vm_area_struct *vma, unsigned long addr,
>  
>  out:
>  		mutex_unlock(&encl->lock);
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  
>  		if (ret)
>  			break;
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index d8c3c07badb3..da3b569a10bd 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -147,6 +147,7 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
>  static long sgx_ioc_enclave_create(struct sgx_encl *encl, void __user *arg)
>  {
>  	struct sgx_enclave_create create_arg;
> +	int srcu_idx;
>  	void *secs;
>  	int ret;
>  
> @@ -162,9 +163,18 @@ static long sgx_ioc_enclave_create(struct sgx_encl *encl, void __user *arg)
>  
>  	if (copy_from_user(secs, (void __user *)create_arg.src, PAGE_SIZE))
>  		ret = -EFAULT;
> -	else
> +	else {
> +		srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +		if (sgx_epc_is_locked()) {
> +			srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +			return -EBUSY;
> +		}
> +
>  		ret = sgx_encl_create(encl, secs);
>  
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +	}
> +
>  	kfree(secs);
>  	return ret;
>  }
> @@ -444,6 +454,7 @@ static long sgx_ioc_enclave_add_pages(struct sgx_encl *encl, void __user *arg)
>  	struct sgx_enclave_add_pages add_arg;
>  	struct sgx_secinfo secinfo;
>  	unsigned long c;
> +	int srcu_idx;
>  	int ret;
>  
>  	if (!test_bit(SGX_ENCL_CREATED, &encl->flags) ||
> @@ -477,8 +488,18 @@ static long sgx_ioc_enclave_add_pages(struct sgx_encl *encl, void __user *arg)
>  		if (need_resched())
>  			cond_resched();
>  
> +		srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +		if (sgx_epc_is_locked()) {
> +			ret = -EBUSY;
> +			srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +			break;
> +		}
> +
>  		ret = sgx_encl_add_page(encl, add_arg.src + c, add_arg.offset + c,
>  					&secinfo, add_arg.flags);
> +
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +
>  		if (ret)
>  			break;
>  	}
> @@ -952,6 +973,7 @@ static long sgx_enclave_restrict_perm(struct sgx_encl *encl,
>  	unsigned long addr;
>  	unsigned long c;
>  	void *epc_virt;
> +	int srcu_idx;
>  	int ret;
>  
>  	memset(&secinfo, 0, sizeof(secinfo));
> @@ -960,6 +982,12 @@ static long sgx_enclave_restrict_perm(struct sgx_encl *encl,
>  	vm_prot = vm_prot_from_secinfo(secinfo_perm);
>  
>  	for (c = 0 ; c < modp->length; c += PAGE_SIZE) {
> +		srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +		if (sgx_epc_is_locked()) {
> +			srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +			return -EBUSY;
> +		}
> +
>  		addr = encl->base + modp->offset + c;
>  
>  		sgx_direct_reclaim();
> @@ -1049,6 +1077,7 @@ static long sgx_enclave_restrict_perm(struct sgx_encl *encl,
>  
>  		sgx_mark_page_reclaimable(entry->epc_page);
>  		mutex_unlock(&encl->lock);
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  	}
>  
>  	ret = 0;
> @@ -1060,6 +1089,7 @@ static long sgx_enclave_restrict_perm(struct sgx_encl *encl,
>  	sgx_mark_page_reclaimable(entry->epc_page);
>  out_unlock:
>  	mutex_unlock(&encl->lock);
> +	srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  out:
>  	modp->count = c;
>  
> @@ -1143,6 +1173,7 @@ static long sgx_enclave_modt(struct sgx_encl *encl,
>  	unsigned long addr;
>  	unsigned long c;
>  	void *epc_virt;
> +	int srcu_idx;
>  	int ret;
>  
>  	/*
> @@ -1156,6 +1187,12 @@ static long sgx_enclave_modt(struct sgx_encl *encl,
>  	secinfo.flags = page_type << 8;
>  
>  	for (c = 0 ; c < modt->length; c += PAGE_SIZE) {
> +		srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +		if (sgx_epc_is_locked()) {
> +			srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +			return -EBUSY;
> +		}
> +
>  		addr = encl->base + modt->offset + c;
>  
>  		sgx_direct_reclaim();
> @@ -1255,6 +1292,7 @@ static long sgx_enclave_modt(struct sgx_encl *encl,
>  		entry->type = page_type;
>  
>  		mutex_unlock(&encl->lock);
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  	}
>  
>  	ret = 0;
> @@ -1265,6 +1303,7 @@ static long sgx_enclave_modt(struct sgx_encl *encl,
>  	entry->vm_run_prot_bits = run_prot_restore;
>  out_unlock:
>  	mutex_unlock(&encl->lock);
> +	srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  out:
>  	modt->count = c;
>  
> @@ -1350,12 +1389,19 @@ static long sgx_encl_remove_pages(struct sgx_encl *encl,
>  	unsigned long addr;
>  	unsigned long c;
>  	void *epc_virt;
> +	int srcu_idx;
>  	int ret;
>  
>  	memset(&secinfo, 0, sizeof(secinfo));
>  	secinfo.flags = SGX_SECINFO_R | SGX_SECINFO_W | SGX_SECINFO_X;
>  
>  	for (c = 0 ; c < params->length; c += PAGE_SIZE) {
> +		srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +		if (sgx_epc_is_locked()) {
> +			srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +			return -EBUSY;
> +		}
> +
>  		addr = encl->base + params->offset + c;
>  
>  		sgx_direct_reclaim();
> @@ -1411,6 +1457,7 @@ static long sgx_encl_remove_pages(struct sgx_encl *encl,
>  		kfree(entry);
>  
>  		mutex_unlock(&encl->lock);
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  	}
>  
>  	ret = 0;
> @@ -1418,6 +1465,7 @@ static long sgx_encl_remove_pages(struct sgx_encl *encl,
>  
>  out_unlock:
>  	mutex_unlock(&encl->lock);
> +	srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  out:
>  	params->count = c;
>  
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 545da16bb3ea..99c86b77ca8f 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -23,6 +23,17 @@ static int sgx_nr_epc_sections;
>  static struct task_struct *ksgxd_tsk;
>  static DECLARE_WAIT_QUEUE_HEAD(ksgxd_waitq);
>  static DEFINE_XARRAY(sgx_epc_address_space);
> +/*
> + * The flag sgx_epc_locked prevents any new SGX flows that
> + * may attempt to allocate a new EPC page.
> + */
> +static bool __rcu sgx_epc_locked;
> +/*
> + * By synchronizing around sgx_epc_locked SRCU ensures that any executing
> + * SGX flows have completed before proceeding with an SVN update. New SGX flows
> + * will be prevented from starting during an SVN update.
> + */
> +DEFINE_SRCU(sgx_lock_epc_srcu);
>  
>  /*
>   * These variables are part of the state of the reclaimer, and must be accessed
> @@ -378,6 +389,8 @@ void sgx_direct_reclaim(void)
>  
>  static int ksgxd(void *p)
>  {
> +	int srcu_idx;
> +
>  	set_freezable();
>  
>  	/*
> @@ -398,9 +411,15 @@ static int ksgxd(void *p)
>  				     kthread_should_stop() ||
>  				     sgx_should_reclaim(SGX_NR_HIGH_PAGES));
>  
> +		srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +		if (sgx_epc_is_locked())
> +			goto maybe_resched;
> +
>  		if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
>  			sgx_reclaim_pages();
>  
> +maybe_resched:
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  		cond_resched();
>  	}
>  
> @@ -943,3 +962,21 @@ static int __init sgx_init(void)
>  }
>  
>  device_initcall(sgx_init);
> +
> +static void sgx_lock_epc(void)
> +{
> +	sgx_epc_locked = true;
> +	synchronize_srcu(&sgx_lock_epc_srcu);
> +}
> +
> +static void sgx_unlock_epc(void)
> +{
> +	sgx_epc_locked = false;
> +	synchronize_srcu(&sgx_lock_epc_srcu);
> +}
> +
> +bool sgx_epc_is_locked(void)
> +{
> +	lockdep_assert_held(&sgx_lock_epc_srcu);
> +	return sgx_epc_locked;
> +}
> diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
> index 6a77a14eee38..e953816d7c8b 100644
> --- a/arch/x86/kernel/cpu/sgx/virt.c
> +++ b/arch/x86/kernel/cpu/sgx/virt.c
> @@ -75,10 +75,21 @@ static vm_fault_t sgx_vepc_fault(struct vm_fault *vmf)
>  {
>  	struct vm_area_struct *vma = vmf->vma;
>  	struct sgx_vepc *vepc = vma->vm_private_data;
> +	int srcu_idx;
>  	int ret;
>  
>  	mutex_lock(&vepc->lock);
> +	srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +
> +	if (sgx_epc_is_locked()) {
> +		ret = -EBUSY;
> +		goto out_unlock;
> +	}
> +
>  	ret = __sgx_vepc_fault(vepc, vma, vmf->address);
> +
> +out_unlock:
> +	srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
>  	mutex_unlock(&vepc->lock);
>  
>  	if (!ret)
> @@ -331,6 +342,7 @@ int __init sgx_vepc_init(void)
>  int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
>  		     int *trapnr)
>  {
> +	int srcu_idx;
>  	int ret;
>  
>  	/*
> @@ -347,6 +359,12 @@ int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
>  	if (WARN_ON_ONCE(!access_ok(secs, PAGE_SIZE)))
>  		return -EINVAL;
>  
> +	srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> +	if (sgx_epc_is_locked()) {
> +		srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +		return -EBUSY;
> +	}
> +
>  	__uaccess_begin();
>  	ret = __ecreate(pageinfo, (void *)secs);
>  	__uaccess_end();
> @@ -356,6 +374,8 @@ int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
>  		return -EFAULT;
>  	}
>  
> +	srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> +
>  	/* ECREATE doesn't return an error code, it faults or succeeds. */
>  	WARN_ON_ONCE(ret);
>  	return 0;
> -- 
> 2.17.1
> 

This series is broken. It does not apply on top of tip/x86/sgx. Also you
forgot CC to me.

BR, Jarkko

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