linux-kernel - [PATCH v2 1/5] Drivers: hv: vmbus: Leak pages if set_memory

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Date: Mon, 11 Mar 2024 09:15:54 -0700
From: mhkelley58@...il.com
To: rick.p.edgecombe@...el.com,
	kys@...rosoft.com,
	haiyangz@...rosoft.com,
	wei.liu@...nel.org,
	decui@...rosoft.com,
	gregkh@...uxfoundation.org,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	kirill.shutemov@...ux.intel.com,
	dave.hansen@...ux.intel.com,
	linux-kernel@...r.kernel.org,
	linux-hyperv@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-coco@...ts.linux.dev
Cc: sathyanarayanan.kuppuswamy@...ux.intel.com,
	elena.reshetova@...el.com
Subject: [PATCH v2 1/5] Drivers: hv: vmbus: Leak pages if set_memory_encrypted() fails

From: Rick Edgecombe <rick.p.edgecombe@...el.com>

In CoCo VMs it is possible for the untrusted host to cause
set_memory_encrypted() or set_memory_decrypted() to fail such that an
error is returned and the resulting memory is shared. Callers need to
take care to handle these errors to avoid returning decrypted (shared)
memory to the page allocator, which could lead to functional or security
issues.

VMBus code could free decrypted pages if set_memory_encrypted()/decrypted()
fails. Leak the pages if this happens.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Signed-off-by: Michael Kelley <mhklinux@...look.com>
---
 drivers/hv/connection.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 3cabeeabb1ca..f001ae880e1d 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -237,8 +237,17 @@ int vmbus_connect(void)
 				vmbus_connection.monitor_pages[0], 1);
 	ret |= set_memory_decrypted((unsigned long)
 				vmbus_connection.monitor_pages[1], 1);
-	if (ret)
+	if (ret) {
+		/*
+		 * If set_memory_decrypted() fails, the encryption state
+		 * of the memory is unknown. So leak the memory instead
+		 * of risking returning decrypted memory to the free list.
+		 * For simplicity, always handle both pages the same.
+		 */
+		vmbus_connection.monitor_pages[0] = NULL;
+		vmbus_connection.monitor_pages[1] = NULL;
 		goto cleanup;
+	}
 
 	/*
 	 * Set_memory_decrypted() will change the memory contents if
@@ -337,13 +346,19 @@ void vmbus_disconnect(void)
 		vmbus_connection.int_page = NULL;
 	}
 
-	set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[0], 1);
-	set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[1], 1);
+	if (vmbus_connection.monitor_pages[0]) {
+		if (!set_memory_encrypted(
+			(unsigned long)vmbus_connection.monitor_pages[0], 1))
+			hv_free_hyperv_page(vmbus_connection.monitor_pages[0]);
+		vmbus_connection.monitor_pages[0] = NULL;
+	}
 
-	hv_free_hyperv_page(vmbus_connection.monitor_pages[0]);
-	hv_free_hyperv_page(vmbus_connection.monitor_pages[1]);
-	vmbus_connection.monitor_pages[0] = NULL;
-	vmbus_connection.monitor_pages[1] = NULL;
+	if (vmbus_connection.monitor_pages[1]) {
+		if (!set_memory_encrypted(
+			(unsigned long)vmbus_connection.monitor_pages[1], 1))
+			hv_free_hyperv_page(vmbus_connection.monitor_pages[1]);
+		vmbus_connection.monitor_pages[1] = NULL;
+	}
 }
 
 /*
-- 
2.25.1