linux-kernel - [PATCH v2 1/6] x86/sgx: Provide indication of life-cycle of EPC pages

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Date:   Mon, 19 Jul 2021 11:20:04 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>
Subject: [PATCH v2 1/6] x86/sgx: Provide indication of life-cycle of EPC pages

SGX EPC pages go through the following life cycle:

	DIRTY ---> FREE ---> IN-USE --\
                    ^                 |
                    \-----------------/

Recovery action for poison for a DIRTY or FREE page is simple. Just
make sure never to allocate the page. IN-USE pages need some extra
handling.

It would be good to use the sgx_epc_page->owner field as an indicator
of where an EPC page is currently in that cycle (owner != NULL means
the EPC page is IN-USE). But there is one caller, sgx_alloc_va_page(),
that calls with NULL.

Make the following changes:

1) Change the type of "owner" to "void *" (it can have other types
   besides "struct sgx_encl_page *).
2) Update sgx_alloc_va_page() to pass in a dummy non-NULL value in
   this case.
3) Add a check to sgx_free_epc_page() to prevent calling with NULL.
4) Reset owner to NULL in sgx_free_epc_page().

Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 arch/x86/kernel/cpu/sgx/encl.c | 2 +-
 arch/x86/kernel/cpu/sgx/main.c | 6 ++++++
 arch/x86/kernel/cpu/sgx/sgx.h  | 2 +-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 001808e3901c..ca328d56d230 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -679,7 +679,7 @@ struct sgx_epc_page *sgx_alloc_va_page(void)
 	struct sgx_epc_page *epc_page;
 	int ret;
 
-	epc_page = sgx_alloc_epc_page(NULL, true);
+	epc_page = sgx_alloc_epc_page("Not NULL!", true);
 	if (IS_ERR(epc_page))
 		return ERR_CAST(epc_page);
 
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 63d3de02bbcc..d61bc1f635a1 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -578,6 +578,11 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
 {
 	struct sgx_epc_page *page;
 
+	if (!owner) {
+		WARN_ON_ONCE(1);
+		return NULL;
+	}
+
 	for ( ; ; ) {
 		page = __sgx_alloc_epc_page();
 		if (!IS_ERR(page)) {
@@ -624,6 +629,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
 
 	spin_lock(&node->lock);
 
+	page->owner = NULL;
 	list_add_tail(&page->list, &node->free_page_list);
 	sgx_nr_free_pages++;
 
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index 4628acec0009..4e1a410b8a62 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -29,7 +29,7 @@
 struct sgx_epc_page {
 	unsigned int section;
 	unsigned int flags;
-	struct sgx_encl_page *owner;
+	void *owner;
 	struct list_head list;
 };
 
-- 
2.29.2