[PATCH] x86/sgx: fix a NULL pointer

[Haitao Huang <haitao.huang@linux.intel.com>]

Under heavy load, the SGX EPC reclaimer (ksgxd) may reclaim the SECS EPC
page for an enclave and set encl->secs.epc_page to NULL. But the SECS
EPC page is used for EAUG in the SGX #PF handler without checking for
NULL and reloading.

Fix this by checking if SECS is loaded before EAUG and loading it if it was
reclaimed.

Fixes: 5a90d2c3f5ef ("x86/sgx: Support adding of pages to an initialized enclave")
Cc: stable@vger.kernel.org
Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
---
 arch/x86/kernel/cpu/sgx/encl.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 2a0e90fe2abc..2ab544da1664 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -235,6 +235,16 @@ static struct sgx_epc_page *sgx_encl_eldu(struct sgx_encl_page *encl_page,
 	return epc_page;
 }
 
+static struct sgx_epc_page *sgx_encl_load_secs(struct sgx_encl *encl)
+{
+	struct sgx_epc_page *epc_page = encl->secs.epc_page;
+
+	if (!epc_page)
+		epc_page = sgx_encl_eldu(&encl->secs, NULL);
+
+	return epc_page;
+}
+
 static struct sgx_encl_page *__sgx_encl_load_page(struct sgx_encl *encl,
 						  struct sgx_encl_page *entry)
 {
@@ -248,11 +258,9 @@ static struct sgx_encl_page *__sgx_encl_load_page(struct sgx_encl *encl,
 		return entry;
 	}
 
-	if (!(encl->secs.epc_page)) {
-		epc_page = sgx_encl_eldu(&encl->secs, NULL);
-		if (IS_ERR(epc_page))
-			return ERR_CAST(epc_page);
-	}
+	epc_page = sgx_encl_load_secs(encl);
+	if (IS_ERR(epc_page))
+		return ERR_CAST(epc_page);
 
 	epc_page = sgx_encl_eldu(entry, encl->secs.epc_page);
 	if (IS_ERR(epc_page))
@@ -339,6 +347,13 @@ static vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
 
 	mutex_lock(&encl->lock);
 
+	epc_page = sgx_encl_load_secs(encl);
+	if (IS_ERR(epc_page)) {
+		if (PTR_ERR(epc_page) == -EBUSY)
+			vmret =  VM_FAULT_NOPAGE;
+		goto err_out_unlock;
+	}
+
 	epc_page = sgx_alloc_epc_page(encl_page, false);
 	if (IS_ERR(epc_page)) {
 		if (PTR_ERR(epc_page) == -EBUSY)
-- 
2.25.1