[PATCH v2 5/5] Drivers: hv: vmbus: Don't free ring buffers that couldn't be re-encrypted

[mhkelley58]

From: Michael Kelley <mhklinux@xxxxxxxxxxx>

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.

The VMBus ring buffer code could free decrypted/shared pages if
set_memory_decrypted() fails. Check the decrypted field in the struct
vmbus_gpadl for the ring buffers to decide whether to free the memory.

Signed-off-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
---
 drivers/hv/channel.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index bb5abdcda18f..47e1bd8de9fc 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -153,7 +153,9 @@ void vmbus_free_ring(struct vmbus_channel *channel)
 	hv_ringbuffer_cleanup(&channel->inbound);
 
 	if (channel->ringbuffer_page) {
-		__free_pages(channel->ringbuffer_page,
+		/* In a CoCo VM leak the memory if it didn't get re-encrypted */
+		if (!channel->ringbuffer_gpadlhandle.decrypted)
+			__free_pages(channel->ringbuffer_page,
 			     get_order(channel->ringbuffer_pagecount
 				       << PAGE_SHIFT));
 		channel->ringbuffer_page = NULL;
-- 
2.25.1