[PATCH 1/4] x86/sgx: Ensure enclave state is visible before marking it created

[Sean Christopherson <sean.j.christopherson@intel.com>]

Add a memory barrier pair to ensure all enclave state is visible in
memory prior to SGX_ENCL_CREATED being set.  Without the barries, adding
pages and/or initializing the enclaves could theoretically consume stale
data.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kernel/cpu/sgx/ioctl.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index 911ff3b0f061..7134d68aecb3 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -163,6 +163,15 @@ static struct sgx_encl_page *sgx_encl_page_alloc(struct sgx_encl *encl,
 	return encl_page;
 }
 
+static bool is_encl_created(struct sgx_encl *encl)
+{
+	bool created = encl->flags & SGX_ENCL_CREATED;
+
+	/* Pairs with smp_wmb() in sgx_encl_create(). */
+	smp_rmb();
+	return created;
+}
+
 static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
 {
 	unsigned long encl_size = secs->size + PAGE_SIZE;
@@ -231,8 +240,9 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
 	/*
 	 * Set SGX_ENCL_CREATED only after the enclave is fully prepped.  This
 	 * allows other flows to check if the enclave has been created without
-	 * taking encl->lock.
+	 * taking encl->lock.  Pairs with smp_rmb() in is_encl_created().
 	 */
+	smp_wmb();
 	encl->flags |= SGX_ENCL_CREATED;
 
 	mutex_unlock(&encl->lock);
@@ -478,7 +488,7 @@ static long sgx_ioc_enclave_add_page(struct file *filep, void __user *arg)
 	struct sgx_enclave_add_page addp;
 	struct sgx_secinfo secinfo;
 
-	if (!(encl->flags & SGX_ENCL_CREATED))
+	if (!is_encl_created(encl))
 		return -EINVAL;
 
 	if (copy_from_user(&addp, arg, sizeof(addp)))
@@ -611,7 +621,7 @@ static long sgx_ioc_enclave_init(struct file *filep, void __user *arg)
 	struct page *initp_page;
 	int ret;
 
-	if (!(encl->flags & SGX_ENCL_CREATED))
+	if (!is_encl_created(encl))
 		return -EINVAL;
 
 	if (copy_from_user(&einit, arg, sizeof(einit)))
-- 
2.22.0