[PATCH AUTOSEL 6.8 39/43] Drivers: hv: vmbus: Don't free ring buffers that couldn't be re-encrypted

[Sasha Levin]

From: Michael Kelley <mhklinux@xxxxxxxxxxx>

[ Upstream commit 30d18df6567be09c1433e81993e35e3da573ac48 ]

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>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240311161558.1310-6-mhklinux@xxxxxxxxxxx
Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
Message-ID: <20240311161558.1310-6-mhklinux@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 98259b4925029..fb8cd8469328e 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;
-- 
2.43.0