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

Wei Liu
2024-03-01T09:26:41Z

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@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/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
>