Drivers: hv: vmbus: Track decrypted status in vmbus_gpadl

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.

In order to make sure callers of vmbus_establish_gpadl() and
vmbus_teardown_gpadl() don't return decrypted/shared pages to
allocators, add a field in struct vmbus_gpadl to keep track of the
decryption status of the buffers. This will allow the callers to
know if they should free or leak the pages.

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/20240311161558.1310-3-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20240311161558.1310-3-mhklinux@outlook.com>

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index adbf674355b2b8a472c03bd60092960cb0c742cf..98259b4925029217b9f1b3fa6c7399f6a984ff24 100644 (file)
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -436,9 +436,18 @@ static int __vmbus_establish_gpadl(struct vmbus_channel *channel,
                (atomic_inc_return(&vmbus_connection.next_gpadl_handle) - 1);
 
        ret = create_gpadl_header(type, kbuffer, size, send_offset, &msginfo);
-       if (ret)
+       if (ret) {
+               gpadl->decrypted = false;
                return ret;
+       }
 
+       /*
+        * Set the "decrypted" flag to true for the set_memory_decrypted()
+        * success case. In the failure case, the encryption state of the
+        * memory is unknown. Leave "decrypted" as true to ensure the
+        * memory will be leaked instead of going back on the free list.
+        */
+       gpadl->decrypted = true;
        ret = set_memory_decrypted((unsigned long)kbuffer,
                                   PFN_UP(size));
        if (ret) {
@@ -527,9 +536,15 @@ cleanup:
 
        kfree(msginfo);
 
-       if (ret)
-               set_memory_encrypted((unsigned long)kbuffer,
-                                    PFN_UP(size));
+       if (ret) {
+               /*
+                * If set_memory_encrypted() fails, the decrypted flag is
+                * left as true so the memory is leaked instead of being
+                * put back on the free list.
+                */
+               if (!set_memory_encrypted((unsigned long)kbuffer, PFN_UP(size)))
+                       gpadl->decrypted = false;
+       }
 
        return ret;
 }
@@ -850,6 +865,8 @@ post_msg_err:
        if (ret)
                pr_warn("Fail to set mem host visibility in GPADL teardown %d.\n", ret);
 
+       gpadl->decrypted = ret;
+
        return ret;
 }
 EXPORT_SYMBOL_GPL(vmbus_teardown_gpadl);

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 6ef0557b4bff8ed5d14bc18391d356913136c23c..96ceb4095425eb39aa8145fda63cc1d859fb56f5 100644 (file)
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -832,6 +832,7 @@ struct vmbus_gpadl {
        u32 gpadl_handle;
        u32 size;
        void *buffer;
+       bool decrypted;
 };
 
 struct vmbus_channel {