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

[Michael Kelley]

From: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> 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@xxxxxxxxxxxxx>
> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> Cc: Wei Liu <wei.liu@xxxxxxxxxx>
> Cc: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Cc: linux-hyperv@xxxxxxxxxxxxxxx
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
>  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