linux-kernel - Re: [PATCH v2 5/5] Drivers: hv: vmbus: Don't free ring buffers that couldn't be re-encrypted

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Date: Tue, 12 Mar 2024 08:16:59 -0700
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: mhklinux@...look.com, rick.p.edgecombe@...el.com, kys@...rosoft.com,
 haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
 gregkh@...uxfoundation.org, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, kirill.shutemov@...ux.intel.com,
 dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org,
 linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
 linux-coco@...ts.linux.dev
Cc: elena.reshetova@...el.com
Subject: Re: [PATCH v2 5/5] Drivers: hv: vmbus: Don't free ring buffers that
 couldn't be re-encrypted


On 3/11/24 9:15 AM, mhkelley58@...il.com wrote:
> From: Michael Kelley <mhklinux@...look.com>
>
> In CoCo VMs 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.
>
> The VMBus ring buffer code could free decrypted/shared pages if
> set_memory_decrypted() fails. Check the decrypted field in the struct
> vmbus_gpadl for the ring buffers to decide whether to free the memory.
>
> Signed-off-by: Michael Kelley <mhklinux@...look.com>
> ---
Looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>  drivers/hv/channel.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> index bb5abdcda18f..47e1bd8de9fc 100644
> --- a/drivers/hv/channel.c
> +++ b/drivers/hv/channel.c
> @@ -153,7 +153,9 @@ void vmbus_free_ring(struct vmbus_channel *channel)
>  	hv_ringbuffer_cleanup(&channel->inbound);
>  
>  	if (channel->ringbuffer_page) {
> -		__free_pages(channel->ringbuffer_page,
> +		/* In a CoCo VM leak the memory if it didn't get re-encrypted */
> +		if (!channel->ringbuffer_gpadlhandle.decrypted)
> +			__free_pages(channel->ringbuffer_page,
>  			     get_order(channel->ringbuffer_pagecount
>  				       << PAGE_SHIFT));
>  		channel->ringbuffer_page = NULL;

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer