From: Michael Kelley <mikelley@microsoft.com>
To: vkuznets <vkuznets@redhat.com>, 163 <freedomsky1986@163.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Wei Liu <wei.liu@kernel.org>,
Tianyu Lan <Tianyu.Lan@microsoft.com>,
KY Srinivasan <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
"Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
Subject: RE: [EXTERNAL] [PATCH 1/5] Drivers: hv: copy from message page only what's needed
Date: Fri, 3 Apr 2020 01:52:52 +0000 [thread overview]
Message-ID: <MW2PR2101MB1052836B9357770FBE0C3825D7C70@MW2PR2101MB1052.namprd21.prod.outlook.com> (raw)
In-Reply-To: <87a73tzwdv.fsf@vitty.brq.redhat.com>
From: Vitaly Kuznetsov <vkuznets@redhat.com> Sent: Thursday, April 2, 2020 9:27 AM
>
> 163 <freedomsky1986@163.com> writes:
>
> > On 4/1/2020 6:36 PM, Vitaly Kuznetsov wrote:
> >> Hyper-V Interrupt Message Page (SIMP) has 16 256-byte slots for
> >> messages. Each message comes with a header (16 bytes) which specifies the
> >> payload length (up to 240 bytes). vmbus_on_msg_dpc(), however, doesn't
> >> look at the real message length and copies the whole slot to a temporary
> >> buffer before passing it to message handlers. This is potentially dangerous
> >> as hypervisor doesn't have to clean the whole slot when putting a new
> >> message there and a message handler can get access to some data which
> >> belongs to a previous message.
> >>
> >> Note, this is not currently a problem because all message handlers are
> >> in-kernel but eventually we may e.g. get this exported to userspace.
> >>
> >> Note also, that this is not a performance critical path: messages (unlike
> >> events) represent rare events so it doesn't really matter (from performance
> >> point of view) if we copy too much.
> >>
> >> Fix the issue by taking into account the real message length. The temporary
> >> buffer allocated by vmbus_on_msg_dpc() remains fixed size for now.
> >>
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> >> ---
> >> drivers/hv/vmbus_drv.c | 3 ++-
> >> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> >> index 029378c27421..2b5572146358 100644
> >> --- a/drivers/hv/vmbus_drv.c
> >> +++ b/drivers/hv/vmbus_drv.c
> >> @@ -1043,7 +1043,8 @@ void vmbus_on_msg_dpc(unsigned long data)
> >> return;
> >>
> >> INIT_WORK(&ctx->work, vmbus_onmessage_work);
> >> - memcpy(&ctx->msg, msg, sizeof(*msg));
> >> + memcpy(&ctx->msg, msg, sizeof(msg->header) +
> >> + msg->header.payload_size);
> >>
> >
> > Hi Vitaly:
> > I think we still need to check whether the payload_size passed from
> > Hyper-V is valid or not here to avoid cross-border issue before doing
> > copying.
>
> Sure,
>
> the header.payload_size must be 0 <= header.payload_size <= 240
>
> I'll add the check.
>
With this change,
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
FWIW, all of this VMbus code, as well as the drivers for the VMbus
synthetic devices, make the fundamental assumption that Hyper-V
is trustworthy and doesn't send any malformed messages. However,
starting this summer we will be submitting changes to "harden" all
of the interactions with Hyper-V to no longer make that assumption.
All relevant fields will be checked before being used so that incorrect
memory references aren't made. This patch is one small step in that
direction. :-)
Michael
next prev parent reply other threads:[~2020-04-03 1:52 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-01 10:36 [PATCH 0/5] Drivers: hv: cleanup VMBus messages handling Vitaly Kuznetsov
2020-04-01 10:36 ` [PATCH 1/5] Drivers: hv: copy from message page only what's needed Vitaly Kuznetsov
2020-04-02 14:46 ` [EXTERNAL] " 163
2020-04-02 16:26 ` Vitaly Kuznetsov
2020-04-03 1:52 ` Michael Kelley [this message]
2020-04-03 7:03 ` Vitaly Kuznetsov
2020-04-01 10:36 ` [PATCH 2/5] Drivers: hv: allocate the exact needed memory for messages Vitaly Kuznetsov
2020-04-03 1:54 ` Michael Kelley
2020-04-01 10:36 ` [PATCH 3/5] Drivers: hv: avoid passing opaque pointer to vmbus_onmessage() Vitaly Kuznetsov
2020-04-03 1:55 ` Michael Kelley
2020-04-01 10:38 ` [PATCH 4/5] Drivers: hv: make sure that 'struct vmbus_channel_message_header' compiles correctly Vitaly Kuznetsov
2020-04-01 10:38 ` [PATCH 5/5] Drivers: hv: check VMBus messages lengths Vitaly Kuznetsov
2020-04-03 2:00 ` Michael Kelley
2020-04-03 7:07 ` Vitaly Kuznetsov
2020-04-03 1:56 ` [PATCH 4/5] Drivers: hv: make sure that 'struct vmbus_channel_message_header' compiles correctly Michael Kelley
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