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

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Date: Fri, 1 Mar 2024 09:26:38 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com, mhklinux@...look.com,
	linux-hyperv@...r.kernel.org, gregkh@...uxfoundation.org,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, netdev@...r.kernel.org,
	kirill.shutemov@...ux.intel.com, dave.hansen@...ux.intel.com,
	linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
	sathyanarayanan.kuppuswamy@...ux.intel.com,
	elena.reshetova@...el.com
Subject: Re: [RFC RFT PATCH 1/4] hv: Leak pages if set_memory_encrypted()
 fails

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@...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.

Thanks,
Wei.

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