[PATCH v3 17/28] x86/sgx: fix a NULL pointer

Haitao Huang
2023-07-12T23:03:19Z

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

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

Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
---
arch/x86/kernel/cpu/sgx/encl.c | 30 +++++++++++++++++++++++-------
arch/x86/kernel/cpu/sgx/main.c | 4 ++++
2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index c321c848baa9..028d1b9d6572 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -235,6 +235,19 @@ 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);
+ if (!IS_ERR(epc_page))
+ sgx_record_epc_page(epc_page, SGX_EPC_OWNER_ENCL_PAGE |
+ SGX_EPC_PAGE_UNRECLAIMABLE);
+ }
+ return epc_page;
+}
+
static struct sgx_encl_page *__sgx_encl_load_page(struct sgx_encl *encl,
struct sgx_encl_page *entry)
{
@@ -248,13 +261,9 @@ 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);
- sgx_record_epc_page(epc_page, SGX_EPC_OWNER_ENCL_PAGE |
- SGX_EPC_PAGE_UNRECLAIMABLE);
- }
+ 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))
@@ -342,6 +351,13 @@ 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)
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 9ea487469e4c..68c89d575abc 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -265,6 +265,10 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,

mutex_lock(&encl->lock);

+ /* Should not be possible */
+ if (WARN_ON(!(encl->secs.epc_page)))
+ goto out;
+
sgx_encl_ewb(epc_page, backing);
encl_page->epc_page = NULL;
encl->secs_child_cnt--;
--
2.25.1