[PATCH v3 17/17] x86/sgx: Fix pages in the BLOCKED state ending up to the free pool

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

A blocked page can end up legitly to the free pool if pinning fails because
we interpret that as an EWB failure and simply put it to the free pool.
This corrupts the EPC page allocator.

Fix the bug by pinning the backing storage when picking the victim pages. A
clean rollback can still be done when the memory allocation fails as pages
can be still returned back to the enclave.

This in effect removes any other failure cases from sgx_encl_ewb() other
than EPCM conflict when the host has went through a sleep cycle. In that
case putting a page back to the free pool is perfectly fine because it is
uninitialized.

Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Shay Katz-zamir <shay.katz-zamir@intel.com>
Cc: Serge Ayoun <serge.ayoun@intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
---
 arch/x86/kernel/cpu/sgx/reclaim.c | 95 ++++++++++++++++++-------------
 1 file changed, 57 insertions(+), 38 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/reclaim.c b/arch/x86/kernel/cpu/sgx/reclaim.c
index 7d628a1388e2..d6e580e55456 100644
--- a/arch/x86/kernel/cpu/sgx/reclaim.c
+++ b/arch/x86/kernel/cpu/sgx/reclaim.c
@@ -206,32 +206,24 @@ static void sgx_reclaimer_block(struct sgx_epc_page *epc_page)
 
 static int __sgx_encl_ewb(struct sgx_encl *encl, struct sgx_epc_page *epc_page,
 			  struct sgx_va_page *va_page, unsigned int va_offset,
-			  unsigned int page_index)
+			  struct sgx_backing *backing)
 {
 	struct sgx_pageinfo pginfo;
-	struct sgx_backing b;
 	int ret;
 
-	ret = sgx_encl_get_backing(encl, page_index, &b);
-	if (ret)
-		return ret;
-
 	pginfo.addr = 0;
-	pginfo.contents = (unsigned long)kmap_atomic(b.contents);
-	pginfo.metadata = (unsigned long)kmap_atomic(b.pcmd) + b.pcmd_offset;
 	pginfo.secs = 0;
+
+	pginfo.contents = (unsigned long)kmap_atomic(backing->contents);
+	pginfo.metadata = (unsigned long)kmap_atomic(backing->pcmd) +
+			  backing->pcmd_offset;
+
 	ret = __ewb(&pginfo, sgx_epc_addr(epc_page),
 		    sgx_epc_addr(va_page->epc_page) + va_offset);
-	kunmap_atomic((void *)(unsigned long)(pginfo.metadata - b.pcmd_offset));
-	kunmap_atomic((void *)(unsigned long)pginfo.contents);
 
-	if (!ret) {
-		set_page_dirty(b.pcmd);
-		set_page_dirty(b.contents);
-	}
-
-	put_page(b.pcmd);
-	put_page(b.contents);
+	kunmap_atomic((void *)(unsigned long)(pginfo.metadata -
+					      backing->pcmd_offset));
+	kunmap_atomic((void *)(unsigned long)pginfo.contents);
 
 	return ret;
 }
@@ -265,7 +257,7 @@ static const cpumask_t *sgx_encl_ewb_cpumask(struct sgx_encl *encl)
 }
 
 static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
-			 unsigned int page_index)
+			 struct sgx_backing *backing)
 {
 	struct sgx_encl_page *encl_page = epc_page->owner;
 	struct sgx_encl *encl = encl_page->encl;
@@ -281,8 +273,7 @@ static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
 	if (sgx_va_page_full(va_page))
 		list_move_tail(&va_page->list, &encl->va_pages);
 
-	ret = __sgx_encl_ewb(encl, epc_page, va_page, va_offset,
-			     page_index);
+	ret = __sgx_encl_ewb(encl, epc_page, va_page, va_offset, backing);
 	if (ret == SGX_NOT_TRACKED) {
 		ret = __etrack(sgx_epc_addr(encl->secs.epc_page));
 		if (ret) {
@@ -292,7 +283,7 @@ static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
 		}
 
 		ret = __sgx_encl_ewb(encl, epc_page, va_page, va_offset,
-				     page_index);
+				     backing);
 		if (ret == SGX_NOT_TRACKED) {
 			/*
 			 * Slow path, send IPIs to kick cpus out of the
@@ -304,7 +295,7 @@ static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
 			on_each_cpu_mask(sgx_encl_ewb_cpumask(encl),
 					 sgx_ipi_cb, NULL, 1);
 			ret = __sgx_encl_ewb(encl, epc_page, va_page,
-					     va_offset, page_index);
+					     va_offset, backing);
 		}
 	}
 
@@ -314,15 +305,20 @@ static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
 
 		sgx_encl_destroy(encl);
 	} else {
+		set_page_dirty(backing->pcmd);
+		set_page_dirty(backing->contents);
+
 		encl_page->desc |= va_offset;
 		encl_page->va_page = va_page;
 	}
 }
 
-static void sgx_reclaimer_write(struct sgx_epc_page *epc_page)
+static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
+				struct sgx_backing *backing)
 {
 	struct sgx_encl_page *encl_page = epc_page->owner;
 	struct sgx_encl *encl = encl_page->encl;
+	struct sgx_backing secs_backing;
 	int ret;
 
 	mutex_lock(&encl->lock);
@@ -331,7 +327,7 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page)
 		ret = __eremove(sgx_epc_addr(epc_page));
 		WARN(ret, "EREMOVE returned %d\n", ret);
 	} else {
-		sgx_encl_ewb(epc_page, SGX_ENCL_PAGE_INDEX(encl_page));
+		sgx_encl_ewb(epc_page, backing);
 	}
 
 	encl_page->epc_page = NULL;
@@ -340,10 +336,17 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page)
 	if (!encl->secs_child_cnt &&
 	    (atomic_read(&encl->flags) &
 	     (SGX_ENCL_DEAD | SGX_ENCL_INITIALIZED))) {
-		sgx_encl_ewb(encl->secs.epc_page, PFN_DOWN(encl->size));
-		sgx_free_page(encl->secs.epc_page);
+		ret = sgx_encl_get_backing(encl, PFN_DOWN(encl->size),
+					   &secs_backing);
+		if (!ret) {
+			sgx_encl_ewb(encl->secs.epc_page, &secs_backing);
+			sgx_free_page(encl->secs.epc_page);
+
+			encl->secs.epc_page = NULL;
 
-		encl->secs.epc_page = NULL;
+			put_page(secs_backing.pcmd);
+			put_page(secs_backing.contents);
+		}
 	}
 
 	mutex_unlock(&encl->lock);
@@ -351,17 +354,21 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page)
 
 /**
  * sgx_reclaim_pages() - Reclaim EPC pages from the consumers
- * Takes a fixed chunk of pages from the global list of consumed EPC pages and
- * tries to swap them. Only the pages that are either being freed by the
- * consumer or actively used are skipped.
+ *
+ * Take a fixed number of pages from the head of the active page pool and
+ * reclaim them to the enclave's private shmem files. Skip the pages, which
+ * have been accessed since the last scan. Move those pages to the tail of
+ * active page pool so that the pages get scanned in LRU like fashion.
  */
 void sgx_reclaim_pages(void)
 {
-	struct sgx_epc_page *chunk[SGX_NR_TO_SCAN + 1];
+	struct sgx_epc_page *chunk[SGX_NR_TO_SCAN];
+	struct sgx_backing backing[SGX_NR_TO_SCAN];
 	struct sgx_epc_section *section;
 	struct sgx_encl_page *encl_page;
 	struct sgx_epc_page *epc_page;
 	int cnt = 0;
+	int ret;
 	int i;
 
 	spin_lock(&sgx_active_page_list_lock);
@@ -388,13 +395,21 @@ void sgx_reclaim_pages(void)
 		epc_page = chunk[i];
 		encl_page = epc_page->owner;
 
-		if (sgx_can_reclaim(epc_page)) {
-			mutex_lock(&encl_page->encl->lock);
-			encl_page->desc |= SGX_ENCL_PAGE_RECLAIMED;
-			mutex_unlock(&encl_page->encl->lock);
-			continue;
-		}
+		if (!sgx_can_reclaim(epc_page))
+			goto skip;
 
+		ret = sgx_encl_get_backing(encl_page->encl,
+					   SGX_ENCL_PAGE_INDEX(encl_page),
+					   &backing[i]);
+		if (ret)
+			goto skip;
+
+		mutex_lock(&encl_page->encl->lock);
+		encl_page->desc |= SGX_ENCL_PAGE_RECLAIMED;
+		mutex_unlock(&encl_page->encl->lock);
+		continue;
+
+skip:
 		kref_put(&encl_page->encl->refcount, sgx_encl_release);
 
 		spin_lock(&sgx_active_page_list_lock);
@@ -416,7 +431,11 @@ void sgx_reclaim_pages(void)
 			continue;
 
 		encl_page = epc_page->owner;
-		sgx_reclaimer_write(epc_page);
+		sgx_reclaimer_write(epc_page, &backing[i]);
+
+		put_page(backing->pcmd);
+		put_page(backing->contents);
+
 		kref_put(&encl_page->encl->refcount, sgx_encl_release);
 		epc_page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
 
-- 
2.20.1