RE: [RFC RFT PATCH 4/4] uio_hv_generic: Don't free decrypted memory

Michael Kelley
2024-03-01T19:01:25Z

From: Rick Edgecombe <rick.p.edgecombe@intel.com> Sent: Wednesday, February 21, 2024 6:10 PM
>
> On TDX it is possible for the untrusted host to cause

Same comment about TDX vs. CoCo VM.

> 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.
>
> uio_hv_generic 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/uio/uio_hv_generic.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/uio/uio_hv_generic.c b/drivers/uio/uio_hv_generic.c
> index 20d9762331bd..6be3462b109f 100644
> --- a/drivers/uio/uio_hv_generic.c
> +++ b/drivers/uio/uio_hv_generic.c
> @@ -181,12 +181,14 @@ hv_uio_cleanup(struct hv_device *dev, struct
> hv_uio_private_data *pdata)
> {
> if (pdata->send_gpadl.gpadl_handle) {
> vmbus_teardown_gpadl(dev->channel, &pdata->send_gpadl);
> - vfree(pdata->send_buf);
> + if (!pdata->send_gpadl.decrypted)
> + vfree(pdata->send_buf);
> }
>
> if (pdata->recv_gpadl.gpadl_handle) {
> vmbus_teardown_gpadl(dev->channel, &pdata->recv_gpadl);
> - vfree(pdata->recv_buf);
> + if (!pdata->recv_gpadl.decrypted)
> + vfree(pdata->recv_buf);
> }
> }
>
> @@ -295,7 +297,8 @@ hv_uio_probe(struct hv_device *dev,
> ret = vmbus_establish_gpadl(channel, pdata->recv_buf,
> RECV_BUFFER_SIZE, &pdata->recv_gpadl);
> if (ret) {
> - vfree(pdata->recv_buf);
> + if (!pdata->recv_gpadl.decrypted)
> + vfree(pdata->recv_buf);
> goto fail_close;
> }
>
> @@ -317,7 +320,8 @@ hv_uio_probe(struct hv_device *dev,
> ret = vmbus_establish_gpadl(channel, pdata->send_buf,
> SEND_BUFFER_SIZE, &pdata->send_gpadl);
> if (ret) {
> - vfree(pdata->send_buf);
> + if (!pdata->send_gpadl.decrypted)
> + vfree(pdata->send_buf);
> goto fail_close;
> }
>
> --
> 2.34.1