linux-kernel - RE: [RFC RFT PATCH 3/4] hv_nstvsc: Don't free decrypted memory

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Date: Fri, 1 Mar 2024 19:01:08 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>, "kys@...rosoft.com"
	<kys@...rosoft.com>, "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
	"wei.liu@...nel.org" <wei.liu@...nel.org>, "decui@...rosoft.com"
	<decui@...rosoft.com>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "gregkh@...uxfoundation.org"
	<gregkh@...uxfoundation.org>, "davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>, "kuba@...nel.org"
	<kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "sathyanarayanan.kuppuswamy@...ux.intel.com"
	<sathyanarayanan.kuppuswamy@...ux.intel.com>, "elena.reshetova@...el.com"
	<elena.reshetova@...el.com>
Subject: RE: [RFC RFT PATCH 3/4] hv_nstvsc: Don't free decrypted memory

From: Rick Edgecombe <rick.p.edgecombe@...el.com> Sent: Wednesday, February 21, 2024 6:10 PM
> 

"Subject:" prefix should be hv_netvsc:

> On TDX it is possible for the untrusted host to cause

Same comment about TDX vs. CoCo VM.

> 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.
> 
> hv_nstvsc could free decrypted/shared pages if set_memory_decrypted()

s/hv_nstvsc/hv_netvsc/

> fails. Check the decrypted field in the gpadl before freeing in order to
> not leak the memory.
> 
> 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/net/hyperv/netvsc.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
> index a6fcbda64ecc..2b6ec979a62f 100644
> --- a/drivers/net/hyperv/netvsc.c
> +++ b/drivers/net/hyperv/netvsc.c
> @@ -154,8 +154,11 @@ static void free_netvsc_device(struct rcu_head
> *head)
>  	int i;
> 
>  	kfree(nvdev->extension);
> -	vfree(nvdev->recv_buf);
> -	vfree(nvdev->send_buf);
> +
> +	if (!nvdev->recv_buf_gpadl_handle.decrypted)
> +		vfree(nvdev->recv_buf);
> +	if (!nvdev->send_buf_gpadl_handle.decrypted)
> +		vfree(nvdev->send_buf);
>  	bitmap_free(nvdev->send_section_map);
> 
>  	for (i = 0; i < VRSS_CHANNEL_MAX; i++) {
> --
> 2.34.1