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From: Rick Edgecombe <rick.p.edgecombe@intel.com>
To: kys@microsoft.com,
	haiyangz@microsoft.com,
	wei.liu@kernel.org,
	decui@microsoft.com,
	mhklinux@outlook.com,
	linux-hyperv@vger.kernel.org,
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Cc: sathyanarayanan.kuppuswamy@linux.intel.com,
	elena.reshetova@intel.com,
	rick.p.edgecombe@intel.com
Subject: [RFC RFT PATCH 1/4] hv: Leak pages if set_memory_encrypted() fails
Date: Wed, 21 Feb 2024 18:10:03 -0800
Message-Id: <20240222021006.2279329-2-rick.p.edgecombe@intel.com>
In-Reply-To: <20240222021006.2279329-1-rick.p.edgecombe@intel.com>
References: <20240222021006.2279329-1-rick.p.edgecombe@intel.com>
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On TDX 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.

Hyperv could free decrypted/shared pages if set_memory_encrypted() fails.
Leak the pages if this happens.

Only compile tested.

Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: linux-hyperv@vger.kernel.org
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 drivers/hv/connection.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 3cabeeabb1ca..e39493421bbb 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -315,6 +315,7 @@ int vmbus_connect(void)
 
 void vmbus_disconnect(void)
 {
+	int ret;
 	/*
 	 * First send the unload request to the host.
 	 */
@@ -337,11 +338,13 @@ 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);
+	ret = set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[0], 1);
+	ret |= set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[1], 1);
 
-	hv_free_hyperv_page(vmbus_connection.monitor_pages[0]);
-	hv_free_hyperv_page(vmbus_connection.monitor_pages[1]);
+	if (!ret) {
+		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;
 }
-- 
2.34.1