[PATCH] Drivers: hv: vmbus: Leak pages if set_memory_encrypted() fails

[libo.chen.cn@windriver.com]

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

commit 03f5a999adba ("Drivers: hv: vmbus: Leak pages if set_memory_encrypted() fails")

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@intel.com>
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/r/20240311161558.1310-2-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20240311161558.1310-2-mhklinux@outlook.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

CVE-2024-36913
Signed-off-by: Libo Chen <libo.chen.cn@windriver.com>
---
This commit is backporting 03f5a999adba to the branch linux-5.15.y to 
solve the CVE-2024-36913. Please merge this commit to linux-5.15.y.
 
 drivers/hv/connection.c | 41 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 47fb412eafd3..8283e7ba156e 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -19,6 +19,7 @@
 #include <linux/vmalloc.h>
 #include <linux/hyperv.h>
 #include <linux/export.h>
+#include <linux/set_memory.h>
 #include <asm/mshyperv.h>
 
 #include "hyperv_vmbus.h"
@@ -216,6 +217,29 @@ int vmbus_connect(void)
 		goto cleanup;
 	}
 
+	ret = set_memory_decrypted((unsigned long)
+				vmbus_connection.monitor_pages[0], 1);
+	ret |= set_memory_decrypted((unsigned long)
+				vmbus_connection.monitor_pages[1], 1);
+	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
+	 * decryption occurs, so zero monitor pages here.
+	 */
+	memset(vmbus_connection.monitor_pages[0], 0x00, HV_HYP_PAGE_SIZE);
+	memset(vmbus_connection.monitor_pages[1], 0x00, HV_HYP_PAGE_SIZE);
+
 	msginfo = kzalloc(sizeof(*msginfo) +
 			  sizeof(struct vmbus_channel_initiate_contact),
 			  GFP_KERNEL);
@@ -303,10 +327,19 @@ void vmbus_disconnect(void)
 		vmbus_connection.int_page = NULL;
 	}
 
-	hv_free_hyperv_page((unsigned long)vmbus_connection.monitor_pages[0]);
-	hv_free_hyperv_page((unsigned long)vmbus_connection.monitor_pages[1]);
-	vmbus_connection.monitor_pages[0] = NULL;
-	vmbus_connection.monitor_pages[1] = NULL;
+	if (vmbus_connection.monitor_pages[0]) {
+		if (!set_memory_encrypted(
+			(unsigned long)vmbus_connection.monitor_pages[0], 1))
+			hv_free_hyperv_page((unsigned long)vmbus_connection.monitor_pages[0]);
+		vmbus_connection.monitor_pages[0] = NULL;
+	}
+
+	if (vmbus_connection.monitor_pages[1]) {
+		if (!set_memory_encrypted(
+			(unsigned long)vmbus_connection.monitor_pages[1], 1))
+			hv_free_hyperv_page((unsigned long)vmbus_connection.monitor_pages[1]);
+		vmbus_connection.monitor_pages[1] = NULL;
+	}
 }
 
 /*
-- 
2.25.1