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From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Wei Hu <weh@microsoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Rob Herring <robh@kernel.org>,
        Krzysztof Wilczynski <kw@linux.com>,
        Bjorn Helgaas <bhelgaas@google.com>
CC:     "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [RFC PATCH 3/4] Drivers: hv: vmbus: Introduce
 vmbus_sendpacket_getid()
Thread-Topic: [RFC PATCH 3/4] Drivers: hv: vmbus: Introduce
 vmbus_sendpacket_getid()
Thread-Index: AQHYQrIr8owmhjFajEK7f8RcR8eP46zZ6ThQ
Date:   Thu, 31 Mar 2022 19:47:32 +0000
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References: <20220328144244.100228-1-parri.andrea@gmail.com>
 <20220328144244.100228-4-parri.andrea@gmail.com>
In-Reply-To: <20220328144244.100228-4-parri.andrea@gmail.com>
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From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Monday, March=
 28, 2022 7:43 AM
>=20
> The function can be used to send a VMbus packet and retrieve the
> corresponding transaction ID.  It will be used by hv_pci.
>=20
> No functional change.
>=20
> Suggested-by: Michael Kelley <mikelley@microsoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> ---
>  drivers/hv/channel.c      | 38 ++++++++++++++++++++++++++++++++------
>  drivers/hv/hyperv_vmbus.h |  2 +-
>  drivers/hv/ring_buffer.c  |  4 +++-
>  include/linux/hyperv.h    |  7 +++++++
>  4 files changed, 43 insertions(+), 8 deletions(-)
>=20
> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> index a253eee3aeb1a..3eaa41c7ce15f 100644
> --- a/drivers/hv/channel.c
> +++ b/drivers/hv/channel.c
> @@ -1022,11 +1022,13 @@ void vmbus_close(struct vmbus_channel *channel)
>  EXPORT_SYMBOL_GPL(vmbus_close);
>=20
>  /**
> - * vmbus_sendpacket() - Send the specified buffer on the given channel
> + * vmbus_sendpacket_getid() - Send the specified buffer on the given cha=
nnel
>   * @channel: Pointer to vmbus_channel structure
>   * @buffer: Pointer to the buffer you want to send the data from.
>   * @bufferlen: Maximum size of what the buffer holds.
>   * @requestid: Identifier of the request
> + * @trans_id: Identifier of the transaction associated to this request, =
if
> + *            the send is successful; undefined, otherwise.
>   * @type: Type of packet that is being sent e.g. negotiate, time
>   *	  packet etc.
>   * @flags: 0 or VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED
> @@ -1036,8 +1038,8 @@ EXPORT_SYMBOL_GPL(vmbus_close);
>   *
>   * Mainly used by Hyper-V drivers.
>   */
> -int vmbus_sendpacket(struct vmbus_channel *channel, void *buffer,
> -			   u32 bufferlen, u64 requestid,
> +int vmbus_sendpacket_getid(struct vmbus_channel *channel, void *buffer,
> +			   u32 bufferlen, u64 requestid, u64 *trans_id,
>  			   enum vmbus_packet_type type, u32 flags)
>  {
>  	struct vmpacket_descriptor desc;
> @@ -1063,7 +1065,31 @@ int vmbus_sendpacket(struct vmbus_channel *channel=
,
> void *buffer,
>  	bufferlist[2].iov_base =3D &aligned_data;
>  	bufferlist[2].iov_len =3D (packetlen_aligned - packetlen);
>=20
> -	return hv_ringbuffer_write(channel, bufferlist, num_vecs, requestid);
> +	return hv_ringbuffer_write(channel, bufferlist, num_vecs, requestid, tr=
ans_id);
> +}
> +EXPORT_SYMBOL(vmbus_sendpacket_getid);
> +
> +/**
> + * vmbus_sendpacket() - Send the specified buffer on the given channel
> + * @channel: Pointer to vmbus_channel structure
> + * @buffer: Pointer to the buffer you want to send the data from.
> + * @bufferlen: Maximum size of what the buffer holds.
> + * @requestid: Identifier of the request
> + * @type: Type of packet that is being sent e.g. negotiate, time
> + *	  packet etc.
> + * @flags: 0 or VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED
> + *
> + * Sends data in @buffer directly to Hyper-V via the vmbus.
> + * This will send the data unparsed to Hyper-V.
> + *
> + * Mainly used by Hyper-V drivers.
> + */
> +int vmbus_sendpacket(struct vmbus_channel *channel, void *buffer,
> +		     u32 bufferlen, u64 requestid,
> +		     enum vmbus_packet_type type, u32 flags)
> +{
> +	return vmbus_sendpacket_getid(channel, buffer, bufferlen,
> +				      requestid, NULL, type, flags);
>  }
>  EXPORT_SYMBOL(vmbus_sendpacket);
>=20
> @@ -1122,7 +1148,7 @@ int vmbus_sendpacket_pagebuffer(struct vmbus_channe=
l
> *channel,
>  	bufferlist[2].iov_base =3D &aligned_data;
>  	bufferlist[2].iov_len =3D (packetlen_aligned - packetlen);
>=20
> -	return hv_ringbuffer_write(channel, bufferlist, 3, requestid);
> +	return hv_ringbuffer_write(channel, bufferlist, 3, requestid, NULL);
>  }
>  EXPORT_SYMBOL_GPL(vmbus_sendpacket_pagebuffer);
>=20
> @@ -1160,7 +1186,7 @@ int vmbus_sendpacket_mpb_desc(struct vmbus_channel
> *channel,
>  	bufferlist[2].iov_base =3D &aligned_data;
>  	bufferlist[2].iov_len =3D (packetlen_aligned - packetlen);
>=20
> -	return hv_ringbuffer_write(channel, bufferlist, 3, requestid);
> +	return hv_ringbuffer_write(channel, bufferlist, 3, requestid, NULL);
>  }
>  EXPORT_SYMBOL_GPL(vmbus_sendpacket_mpb_desc);
>=20
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index 3a1f007b678a0..64c0b9cbe183b 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -181,7 +181,7 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info
> *ring_info);
>=20
>  int hv_ringbuffer_write(struct vmbus_channel *channel,
>  			const struct kvec *kv_list, u32 kv_count,
> -			u64 requestid);
> +			u64 requestid, u64 *trans_id);
>=20
>  int hv_ringbuffer_read(struct vmbus_channel *channel,
>  		       void *buffer, u32 buflen, u32 *buffer_actual_len,
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 71efacb909659..c8561c80c460c 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -283,7 +283,7 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info
> *ring_info)
>  /* Write to the ring buffer. */
>  int hv_ringbuffer_write(struct vmbus_channel *channel,
>  			const struct kvec *kv_list, u32 kv_count,
> -			u64 requestid)
> +			u64 requestid, u64 *trans_id)
>  {
>  	int i;
>  	u32 bytes_avail_towrite;
> @@ -354,6 +354,8 @@ int hv_ringbuffer_write(struct vmbus_channel *channel=
,
>  	}
>  	desc =3D hv_get_ring_buffer(outring_info) + old_write;
>  	desc->trans_id =3D (rqst_id =3D=3D VMBUS_NO_RQSTOR) ? requestid : rqst_=
id;
> +	if (trans_id)
> +		*trans_id =3D desc->trans_id;

This line should *not* read the trans_id out of the ring buffer, since that
memory is shared with the Hyper-V host and subject to being maliciously
changed by the host.  Need to set *trans_id only from local variables, and
somehow ensure the compiler doesn't generate code that reads the value
from the ring buffer.  Maybe mark the desc->trans_id field as volatile, or =
cast
it as such?  Or does WRITE_ONCE() work when setting it?

Michael

>=20
>  	/* Set previous packet start */
>  	prev_indices =3D hv_get_ring_bufferindices(outring_info);
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index fe2e0179ed51e..a7cb596d893b1 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1161,6 +1161,13 @@ extern int vmbus_open(struct vmbus_channel *channe=
l,
>=20
>  extern void vmbus_close(struct vmbus_channel *channel);
>=20
> +extern int vmbus_sendpacket_getid(struct vmbus_channel *channel,
> +				  void *buffer,
> +				  u32 bufferLen,
> +				  u64 requestid,
> +				  u64 *trans_id,
> +				  enum vmbus_packet_type type,
> +				  u32 flags);
>  extern int vmbus_sendpacket(struct vmbus_channel *channel,
>  				  void *buffer,
>  				  u32 bufferLen,
> --
> 2.25.1