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

Edgecombe, Rick P
2024-03-01T19:12:50Z

On Fri, 2024-03-01 at 09:26 +0000, Wei Liu wrote:
> > Hyperv could free decrypted/shared pages if set_memory_encrypted()
> > fails.
>
> "Hyper-V" throughout.

Ok.

>
> > 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.

Another patch will warn in CPA for the particular case:
https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/mm

Do we want a warning in the caller too? It is more robust to other
types of failures in the future I guess.