From:   Reinette Chatre <reinette.chatre@intel.com>
To:     dave.hansen@linux.intel.com, jarkko@kernel.org, tglx@linutronix.de,
        bp@alien8.de, luto@kernel.org, mingo@redhat.com,
        linux-sgx@vger.kernel.org, x86@kernel.org
Cc:     seanjc@google.com, kai.huang@intel.com, cathy.zhang@intel.com,
        cedric.xing@intel.com, haitao.huang@intel.com,
        mark.shanahan@intel.com, hpa@zytor.com,
        linux-kernel@vger.kernel.org
Subject: [PATCH 16/25] x86/sgx: Support modifying SGX page type
Date:   Wed,  1 Dec 2021 11:23:14 -0800
Message-Id: <c0f04a8f7e1afd9e9319bb9f283db9a3187f7abc.1638381245.git.reinette.chatre@intel.com>
In-Reply-To: <cover.1638381245.git.reinette.chatre@intel.com>
References: <cover.1638381245.git.reinette.chatre@intel.com>
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Every enclave contains one or more Thread Control Structures (TCS). The
TCS contains meta-data used by the hardware to save and restore thread
specific information when entering/exiting the enclave. With SGX1 an
enclave needs to be created with enough TCSs to support the largest
number of threads expecting to use the enclave and enough enclave pages
to meet all its anticipated memory demands. In SGX1 all pages remain in
the enclave until the enclave is unloaded.

Earlier changes added support for the SGX2 feature where pages can be
added dynamically to an initialized enclave.

SGX2 introduces a new function, ENCLS[EMODT], that is used to change
the type of an enclave page from a regular (SGX_PAGE_TYPE_REG) enclave
page to a TCS (SGX_PAGE_TYPE_TCS) page or change the type from a
regular (SGX_PAGE_TYPE_REG) or TCS (SGX_PAGE_TYPE_TCS)
page to a trimmed (SGX_PAGE_TYPE_TRIM) page (setting it up for later
removal).

With the existing support of dynamically adding regular enclave pages
to an initialized enclave and changing the page type to TCS it is
possible to dynamically increase the number of threads supported by an
enclave.

Changing the enclave page type to SGX_PAGE_TYPE_TRIM is the first step
of dynamically removing pages from an initialized enclave. The complete
page removal flow is:
1) Change the type of the pages to be removed to SGX_PAGE_TYPE_TRIM
   using the ioctl introduced here.
2) Approve the page removal by running ENCLU[EACCEPT] from within
   the enclave.
3) Initiate actual page removal using the new ioctl introduced in the
   following patch.

Support changing SGX enclave page types with a new ioctl. With this
ioctl the user specifies a page range and the enclave page type to be
applied to all pages in the provided range. The ioctl itself can return
an error code based on failures encountered by the OS. It is also
possible for SGX specific failures to be encountered.  Add a result
output parameter to communicate the SGX return code. It is
possible for the enclave page type change request to fail on any page
within the provided range. Support partial success by returning
the number of pages that were successfully changed.

After the page type is changed to SGX_PAGE_TYPE_TRIM the page continues
to be accessible from the OS perspective with page table entries and
internal state. The page may be moved to swap. Any invalid access
(any access except ENCLU[EACCEPT]) will encounter a page fault with
SGX flag set in error code until the page is removed. Removal of
trimmed enclave pages on user request will be supported in following
patch. Trimmed enclave pages are also removed when enclave is unloaded.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
 arch/x86/include/uapi/asm/sgx.h |  19 +++
 arch/x86/kernel/cpu/sgx/ioctl.c | 235 ++++++++++++++++++++++++++++++++
 2 files changed, 254 insertions(+)

diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
index 24bebc31e336..f70caccd166c 100644
--- a/arch/x86/include/uapi/asm/sgx.h
+++ b/arch/x86/include/uapi/asm/sgx.h
@@ -31,6 +31,8 @@ enum sgx_page_flags {
 	_IO(SGX_MAGIC, 0x04)
 #define SGX_IOC_PAGE_MODP \
 	_IOWR(SGX_MAGIC, 0x05, struct sgx_page_modp)
+#define SGX_IOC_PAGE_MODT \
+	_IOWR(SGX_MAGIC, 0x06, struct sgx_page_modt)
 
 /**
  * struct sgx_enclave_create - parameter structure for the
@@ -96,6 +98,23 @@ struct sgx_page_modp {
 	__u64 count;
 };
 
+/**
+ * struct sgx_page_modt - parameter structure for the %SGX_IOC_PAGE_MODT ioctl
+ * @offset:	starting page offset (page aligned relative to enclave base
+ *		address defined in SECS)
+ * @length:	length of memory (multiple of the page size)
+ * @type:	new type of pages in range described by @offset and @length
+ * @result:	SGX result code of ENCLS[EMODT] function
+ * @count:	bytes successfully changed (multiple of page size)
+ */
+struct sgx_page_modt {
+	__u64 offset;
+	__u64 length;
+	__u64 type;
+	__u64 result;
+	__u64 count;
+};
+
 struct sgx_enclave_run;
 
 /**
diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index de0bf68ee842..a952d608ab35 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -914,6 +914,238 @@ static long sgx_ioc_page_modp(struct sgx_encl *encl, void __user *arg)
 	return ret;
 }
 
+/**
+ * sgx_page_modt - Modify type of SGX enclave pages
+ * @encl:	Enclave to which the pages belong.
+ * @modt:	Checked parameters from user about which pages need modifying
+ *		and their new type.
+ *
+ * Ability to change the enclave page type supports the following use cases:
+ * * It is possible to add TCS pages to enclave by changing the type of
+ * regular pages (SGX_PAGE_TYPE_REG) to TCS (SGX_PAGE_TYPE_TCS) pages. With
+ * this support the number of threads supported by an initialized enclave
+ * can be increased dynamically.
+ * * Regular or TCS pages can dynamically be removed from an initialized
+ * enclave by changing the page type to SGX_PAGE_TYPE_TRIM. Changing the
+ * page type to SGX_PAGE_TYPE_TRIM marks the page for removal with actual
+ * removal done by handler of %SGX_IOC_PAGE_REMOVE ioctl called after
+ * ENCLU[EACCEPT] is run on SGX_PAGE_TYPE_TRIM page from within the enclave.
+ *
+ * Return:
+ * - 0:		Success
+ * - -errno:	Otherwise
+ */
+static long sgx_page_modt(struct sgx_encl *encl, struct sgx_page_modt *modt)
+{
+	unsigned long max_prot_restore, run_prot_restore;
+	enum sgx_page_type page_type;
+	struct sgx_encl_page *entry;
+	struct sgx_secinfo secinfo;
+	unsigned long prot;
+	unsigned long addr;
+	unsigned long c;
+	void *epc_virt;
+	int ret;
+
+	page_type = modt->type & SGX_PAGE_TYPE_MASK;
+
+	/*
+	 * The only new page types allowed by hardware are PT_TCS and PT_TRIM.
+	 */
+	if (page_type != SGX_PAGE_TYPE_TCS && page_type != SGX_PAGE_TYPE_TRIM)
+		return -EINVAL;
+
+	memset(&secinfo, 0, sizeof(secinfo));
+
+	secinfo.flags = page_type << 8;
+
+	for (c = 0 ; c < modt->length; c += PAGE_SIZE) {
+		addr = encl->base + modt->offset + c;
+
+		mutex_lock(&encl->lock);
+
+		entry = sgx_encl_load_page(encl, addr);
+		if (IS_ERR(entry)) {
+			ret = PTR_ERR(entry) == -EBUSY ? -EAGAIN : -EFAULT;
+			goto out_unlock;
+		}
+
+		/*
+		 * Borrow the logic from the Intel SDM. Regular pages
+		 * (SGX_PAGE_TYPE_REG) can change type to SGX_PAGE_TYPE_TCS
+		 * or SGX_PAGE_TYPE_TRIM but TCS pages can only be trimmed.
+		 * CET pages not supported yet.
+		 */
+		if (!(entry->type == SGX_PAGE_TYPE_REG ||
+		      (entry->type == SGX_PAGE_TYPE_TCS &&
+		       page_type == SGX_PAGE_TYPE_TRIM))) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
+		max_prot_restore = entry->vm_max_prot_bits;
+		run_prot_restore = entry->vm_run_prot_bits;
+
+		/*
+		 * Once a regular page becomes a TCS page it cannot be
+		 * changed back. So the maximum allowed protection reflects
+		 * the TCS page that is always RW from OS perspective but
+		 * will be inaccessible from within enclave. Before doing
+		 * so, do make sure that the new page type continues to
+		 * respect the originally vetted page permissions.
+		 */
+		if (entry->type == SGX_PAGE_TYPE_REG &&
+		    page_type == SGX_PAGE_TYPE_TCS) {
+			if (~entry->vm_max_prot_bits & (VM_READ | VM_WRITE)) {
+				ret = -EPERM;
+				goto out_unlock;
+			}
+			prot = PROT_READ | PROT_WRITE;
+			entry->vm_max_prot_bits = calc_vm_prot_bits(prot, 0);
+			entry->vm_run_prot_bits = entry->vm_max_prot_bits;
+
+			/*
+			 * Prevent page from being reclaimed while mutex
+			 * is released.
+			 */
+			if (sgx_unmark_page_reclaimable(entry->epc_page)) {
+				ret = -EAGAIN;
+				goto out_entry_changed;
+			}
+
+			/*
+			 * Do not keep encl->lock because of dependency on
+			 * mmap_lock acquired in sgx_zap_enclave_ptes().
+			 */
+			mutex_unlock(&encl->lock);
+
+			sgx_zap_enclave_ptes(encl, addr);
+
+			mutex_lock(&encl->lock);
+
+			sgx_mark_page_reclaimable(entry->epc_page);
+		}
+
+		/* Change EPC type */
+		epc_virt = sgx_get_epc_virt_addr(entry->epc_page);
+		ret = __emodt(&secinfo, epc_virt);
+		if (encls_faulted(ret)) {
+			/*
+			 * All possible faults should be avoidable:
+			 * parameters have been checked, will only change
+			 * valid page types, and no concurrent
+			 * SGX1/SGX2 ENCLS instructions since these are
+			 * protected with mutex.
+			 */
+			pr_err_once("EMODT encountered exception %d\n",
+				    ENCLS_TRAPNR(ret));
+			ret = -EFAULT;
+			goto out_entry_changed;
+		}
+		if (encls_failed(ret)) {
+			modt->result = ret;
+			ret = -EFAULT;
+			goto out_entry_changed;
+		}
+
+		epc_virt = sgx_get_epc_virt_addr(encl->secs.epc_page);
+		ret = __etrack(epc_virt);
+		if (ret) {
+			/*
+			 * ETRACK only fails when there is an OS issue. For
+			 * example, two consecutive ETRACK was sent without
+			 * completed IPI between.
+			 */
+			pr_err_once("ETRACK returned %d (0x%x)", ret, ret);
+			/*
+			 * Send IPIs to kick CPUs out of the enclave and
+			 * try ETRACK again.
+			 */
+			on_each_cpu_mask(sgx_encl_cpumask(encl),
+					 sgx_ipi_cb, NULL, 1);
+			ret = __etrack(epc_virt);
+			if (ret) {
+				pr_err_once("ETRACK repeat returned %d (0x%x)",
+					    ret, ret);
+				ret = -EFAULT;
+				goto out_unlock;
+			}
+		}
+		on_each_cpu_mask(sgx_encl_cpumask(encl), sgx_ipi_cb, NULL, 1);
+
+		entry->type = page_type;
+
+		mutex_unlock(&encl->lock);
+	}
+
+	ret = 0;
+	goto out;
+
+out_entry_changed:
+	entry->vm_max_prot_bits = max_prot_restore;
+	entry->vm_run_prot_bits = run_prot_restore;
+out_unlock:
+	mutex_unlock(&encl->lock);
+out:
+	modt->count = c;
+
+	return ret;
+}
+
+/**
+ * sgx_ioc_page_modt() - handler for %SGX_IOC_PAGE_MODT
+ * @encl:	an enclave pointer
+ * @arg:	userspace pointer to a &struct sgx_page_modt instance
+ *
+ * Return:
+ * - 0:		Success
+ * - -errno:	Otherwise
+ */
+static long sgx_ioc_page_modt(struct sgx_encl *encl, void __user *arg)
+{
+	struct sgx_page_modt params;
+	long ret;
+
+	/*
+	 * Ensure that there is a chance the request could succeed:
+	 * (1) SGX2 is required.
+	 * (2) Only pages in an initialized enclave could be modified.
+	 */
+	if (!(cpu_feature_enabled(X86_FEATURE_SGX2)))
+		return -ENODEV;
+
+	if (!test_bit(SGX_ENCL_INITIALIZED, &encl->flags))
+		return -EINVAL;
+
+	/*
+	 * Obtain parameters from user and perform sanity checks.
+	 */
+	if (copy_from_user(&params, arg, sizeof(params)))
+		return -EFAULT;
+
+	if (!IS_ALIGNED(params.offset, PAGE_SIZE))
+		return -EINVAL;
+
+	if (!params.length || params.length & (PAGE_SIZE - 1))
+		return -EINVAL;
+
+	if (params.offset + params.length - PAGE_SIZE >= encl->size)
+		return -EINVAL;
+
+	if (params.type & ~SGX_PAGE_TYPE_MASK)
+		return -EINVAL;
+
+	if (params.result || params.count)
+		return -EINVAL;
+
+	ret = sgx_page_modt(encl, &params);
+
+	if (copy_to_user(arg, &params, sizeof(params)))
+		return -EFAULT;
+
+	return ret;
+}
+
 long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 {
 	struct sgx_encl *encl = filep->private_data;
@@ -938,6 +1170,9 @@ long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 	case SGX_IOC_PAGE_MODP:
 		ret = sgx_ioc_page_modp(encl, (void __user *)arg);
 		break;
+	case SGX_IOC_PAGE_MODT:
+		ret = sgx_ioc_page_modt(encl, (void __user *)arg);
+		break;
 	default:
 		ret = -ENOIOCTLCMD;
 		break;
-- 
2.25.1