[RFC RFT PATCH 3/4] hv_nstvsc: Don't free decrypted memory

Rick Edgecombe
2024-02-22T02:10:45Z

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.

hv_nstvsc could free decrypted/shared pages if set_memory_decrypted()
fails. Check the decrypted field in the gpadl before freeing in order to
not leak the memory.

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/net/hyperv/netvsc.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index a6fcbda64ecc..2b6ec979a62f 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -154,8 +154,11 @@ static void free_netvsc_device(struct rcu_head *head)
int i;

kfree(nvdev->extension);
- vfree(nvdev->recv_buf);
- vfree(nvdev->send_buf);
+
+ if (!nvdev->recv_buf_gpadl_handle.decrypted)
+ vfree(nvdev->recv_buf);
+ if (!nvdev->send_buf_gpadl_handle.decrypted)
+ vfree(nvdev->send_buf);
bitmap_free(nvdev->send_section_map);

for (i = 0; i < VRSS_CHANNEL_MAX; i++) {
--
2.34.1