linux-kernel - [PATCH] x86/sgx: fix a NULL pointer

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Message-Id: <20230717181732.84039-1-haitao.huang@linux.intel.com>
Date:   Mon, 17 Jul 2023 11:17:32 -0700
From:   Haitao Huang <haitao.huang@...ux.intel.com>
To:     jarkko@...nel.org, dave.hansen@...ux.intel.com,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:     kai.huang@...el.com, reinette.chatre@...el.com,
        kristen@...ux.intel.com, seanjc@...gle.com, stable@...r.kernel.org
Subject: [PATCH] x86/sgx: fix a NULL pointer

Under heavy load, the SGX EPC reclaimers (current ksgxd or future EPC
cgroup worker) 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 load it if it was
reclaimed.

Fixes: 5a90d2c3f5ef8 ("x86/sgx: Support adding of pages to an initialized enclave")
Cc: stable@...r.kernel.org
Signed-off-by: Haitao Huang <haitao.huang@...ux.intel.com>
---
 arch/x86/kernel/cpu/sgx/encl.c | 25 ++++++++++++++++++++-----
 arch/x86/kernel/cpu/sgx/main.c |  4 ++++
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 2a0e90fe2abc..d39e502bb7b0 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)
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 166692f2d501..4662a364ce62 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -257,6 +257,10 @@ 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