Re: [RFC RFT PATCH 1/4] hv: Leak pages if set_memory_encrypted() fails

[Wei Liu]

On Wed, Feb 21, 2024 at 06:10:03PM -0800, Rick Edgecombe wrote:
> 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.
> 
> Hyperv could free decrypted/shared pages if set_memory_encrypted() fails.

"Hyper-V" throughout.

> Leak the pages if this happens.
> 
> 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/hv/connection.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index 3cabeeabb1ca..e39493421bbb 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -315,6 +315,7 @@ int vmbus_connect(void)
>  
>  void vmbus_disconnect(void)
>  {
> +	int ret;
>  	/*
>  	 * First send the unload request to the host.
>  	 */
> @@ -337,11 +338,13 @@ void vmbus_disconnect(void)
>  		vmbus_connection.int_page = NULL;
>  	}
>  
> -	set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[0], 1);
> -	set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[1], 1);
> +	ret = set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[0], 1);
> +	ret |= set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[1], 1);
>  
> -	hv_free_hyperv_page(vmbus_connection.monitor_pages[0]);
> -	hv_free_hyperv_page(vmbus_connection.monitor_pages[1]);
> +	if (!ret) {
> +		hv_free_hyperv_page(vmbus_connection.monitor_pages[0]);
> +		hv_free_hyperv_page(vmbus_connection.monitor_pages[1]);
> +	}

This silently leaks the pages if set_memory_encrypted() fails.  I think
there should print some warning or error messages here.

Thanks,
Wei.

>  	vmbus_connection.monitor_pages[0] = NULL;
>  	vmbus_connection.monitor_pages[1] = NULL;
>  }
> -- 
> 2.34.1
>