[PATCH RFC 3/3] x86/sgx: Implement EAUG population with MAP_POPULATE

[Jarkko Sakkinen]

With SGX1 an enclave needs to be created with its maximum memory demands
pre-allocated. Pages cannot be added to an enclave after it is initialized.
SGX2 introduces a new function, ENCLS[EAUG] for adding pages to an
initialized enclave.

Add support for dynamically adding pages to an initialized enclave with
mmap() by populating pages with EAUG. Use f_ops->populate() callback to
achieve this behaviour.

Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
---
 arch/x86/kernel/cpu/sgx/driver.c | 129 +++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
index aa9b8b868867..0e97e7476076 100644
--- a/arch/x86/kernel/cpu/sgx/driver.c
+++ b/arch/x86/kernel/cpu/sgx/driver.c
@@ -9,6 +9,7 @@
 #include <asm/traps.h>
 #include "driver.h"
 #include "encl.h"
+#include "encls.h"
 
 u64 sgx_attributes_reserved_mask;
 u64 sgx_xfrm_reserved_mask = ~0x3;
@@ -101,6 +102,133 @@ static int sgx_mmap(struct file *file, struct vm_area_struct *vma)
 	return 0;
 }
 
+static int sgx_encl_augment_page(struct sgx_encl *encl, unsigned long offset)
+{
+	struct sgx_pageinfo pginfo = {0};
+	struct sgx_encl_page *encl_page;
+	struct sgx_epc_page *epc_page;
+	struct sgx_va_page *va_page;
+	u64 secinfo_flags;
+	int ret;
+
+	/*
+	 * Ignore internal permission checking for dynamically added pages.
+	 * They matter only for data added during the pre-initialization phase.
+	 * The enclave decides the permissions by the means of EACCEPT,
+	 * EACCEPTCOPY and EMODPE.
+	 */
+	secinfo_flags = SGX_SECINFO_R | SGX_SECINFO_W | SGX_SECINFO_X;
+	encl_page = sgx_encl_page_alloc(encl, offset, secinfo_flags);
+	if (IS_ERR(encl_page))
+		return PTR_ERR(encl_page);
+
+	epc_page = sgx_alloc_epc_page(encl_page, true);
+	if (IS_ERR(epc_page)) {
+		ret = PTR_ERR(epc_page);
+		goto err_alloc_epc_page;
+	}
+
+	va_page = sgx_encl_grow(encl);
+	if (IS_ERR(va_page)) {
+		ret = PTR_ERR(va_page);
+		goto err_grow;
+	}
+
+	mutex_lock(&encl->lock);
+
+	/*
+	 * Adding to encl->va_pages must be done under encl->lock.  Ditto for
+	 * deleting (via sgx_encl_shrink()) in the error path.
+	 */
+	if (va_page)
+		list_add(&va_page->list, &encl->va_pages);
+
+	/*
+	 * Insert prior to EADD in case of OOM.  EADD modifies MRENCLAVE, i.e.
+	 * can't be gracefully unwound, while failure on EADD/EXTEND is limited
+	 * to userspace errors (or kernel/hardware bugs).
+	 */
+	ret = xa_insert(&encl->page_array, PFN_DOWN(encl_page->desc),
+			encl_page, GFP_KERNEL);
+
+	/*
+	 * If ret == -EBUSY then page was created in another flow while
+	 * running without encl->lock
+	 */
+	if (ret)
+		goto err_xa_insert;
+
+	pginfo.secs = (unsigned long)sgx_get_epc_virt_addr(encl->secs.epc_page);
+	pginfo.addr = encl_page->desc & PAGE_MASK;
+	pginfo.metadata = 0;
+
+	ret = __eaug(&pginfo, sgx_get_epc_virt_addr(epc_page));
+	if (ret)
+		goto err_eaug;
+
+	encl_page->encl = encl;
+	encl_page->epc_page = epc_page;
+	encl_page->type = SGX_PAGE_TYPE_REG;
+	encl->secs_child_cnt++;
+
+	sgx_mark_page_reclaimable(encl_page->epc_page);
+
+	mutex_unlock(&encl->lock);
+
+	return 0;
+
+err_eaug:
+	xa_erase(&encl->page_array, PFN_DOWN(encl_page->desc));
+
+err_xa_insert:
+	sgx_encl_shrink(encl, va_page);
+	mutex_unlock(&encl->lock);
+
+err_grow:
+	sgx_encl_free_epc_page(epc_page);
+
+err_alloc_epc_page:
+	kfree(encl_page);
+
+	return VM_FAULT_SIGBUS;
+}
+
+/*
+ * Add new pages to the enclave sequentially with ENCLS[EAUG]. Note that
+ * sgx_mmap() validates that the given VMA is within the enclave range. Calling
+ * here sgx_encl_may_map() second time would too time consuming.
+ */
+static int sgx_populate(struct file *file, struct vm_area_struct *vma)
+{
+	unsigned long length = vma->vm_end - vma->vm_start;
+	struct sgx_encl *encl = file->private_data;
+	unsigned long start = encl->base - vma->vm_start;
+	unsigned long pos;
+	int ret;
+
+	/* EAUG works only for initialized enclaves. */
+	if (!test_bit(SGX_ENCL_INITIALIZED, &encl->flags))
+		return -EINVAL;
+
+	for (pos = 0 ; pos < length; pos += PAGE_SIZE) {
+		if (signal_pending(current)) {
+			if (!pos)
+				ret = -ERESTARTSYS;
+
+			break;
+		}
+
+		if (need_resched())
+			cond_resched();
+
+		ret = sgx_encl_augment_page(encl, start + pos);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
 static unsigned long sgx_get_unmapped_area(struct file *file,
 					   unsigned long addr,
 					   unsigned long len,
@@ -133,6 +261,7 @@ static const struct file_operations sgx_encl_fops = {
 	.compat_ioctl		= sgx_compat_ioctl,
 #endif
 	.mmap			= sgx_mmap,
+	.populate		= sgx_populate,
 	.get_unmapped_area	= sgx_get_unmapped_area,
 };
 
-- 
2.35.1