linux-kernel - Re: [RFC RFT PATCH 1/4] hv: Leak pages if set_memory

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Date: Fri, 1 Mar 2024 19:12:45 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "wei.liu@...nel.org" <wei.liu@...nel.org>
CC: "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
	"mhklinux@...look.com" <mhklinux@...look.com>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "davem@...emloft.net" <davem@...emloft.net>,
	"haiyangz@...rosoft.com" <haiyangz@...rosoft.com>, "Reshetova, Elena"
	<elena.reshetova@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"pabeni@...hat.com" <pabeni@...hat.com>, "kirill.shutemov@...ux.intel.com"
	<kirill.shutemov@...ux.intel.com>, "kys@...rosoft.com" <kys@...rosoft.com>,
	"Cui, Dexuan" <decui@...rosoft.com>, "kuba@...nel.org" <kuba@...nel.org>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"sathyanarayanan.kuppuswamy@...ux.intel.com"
	<sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [RFC RFT PATCH 1/4] hv: Leak pages if set_memory_encrypted()
 fails

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@...rosoft.com>
> > Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> > Cc: Wei Liu <wei.liu@...nel.org>
> > Cc: Dexuan Cui <decui@...rosoft.com>
> > Cc: linux-hyperv@...r.kernel.org
> > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.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.