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From:   "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
To:     linux-kernel@vger.kernel.org
Cc:     "K . Y . Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        linux-hyperv@vger.kernel.org,
        Tianyu Lan <Tianyu.Lan@microsoft.com>,
        Saruhan Karademir <skarade@microsoft.com>,
        Juan Vazquez <juvazq@microsoft.com>,
        "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
Subject: [PATCH v2 2/4] Drivers: hv: vmbus: Restrict vmbus_devices on isolated guests
Date:   Tue, 26 Jan 2021 12:56:39 +0100
Message-Id: <20210126115641.2527-3-parri.andrea@gmail.com>
In-Reply-To: <20210126115641.2527-1-parri.andrea@gmail.com>
References: <20210126115641.2527-1-parri.andrea@gmail.com>
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Only the VSCs or ICs that have been hardened and that are critical for
the successful adoption of Confidential VMs should be allowed if the
guest is running isolated.  This change reduces the footprint of the
code that will be exercised by Confidential VMs and hence the exposure
to bugs and vulnerabilities.

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
---
 drivers/hv/channel_mgmt.c | 36 ++++++++++++++++++++++++++++++++++++
 include/linux/hyperv.h    |  1 +
 2 files changed, 37 insertions(+)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 68950a1e4b638..774ee19e3e90d 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -31,101 +31,118 @@ const struct vmbus_device vmbus_devs[] = {
 	{ .dev_type = HV_IDE,
 	  HV_IDE_GUID,
 	  .perf_device = true,
+	  .allowed_in_isolated = false,
 	},
 
 	/* SCSI */
 	{ .dev_type = HV_SCSI,
 	  HV_SCSI_GUID,
 	  .perf_device = true,
+	  .allowed_in_isolated = true,
 	},
 
 	/* Fibre Channel */
 	{ .dev_type = HV_FC,
 	  HV_SYNTHFC_GUID,
 	  .perf_device = true,
+	  .allowed_in_isolated = false,
 	},
 
 	/* Synthetic NIC */
 	{ .dev_type = HV_NIC,
 	  HV_NIC_GUID,
 	  .perf_device = true,
+	  .allowed_in_isolated = true,
 	},
 
 	/* Network Direct */
 	{ .dev_type = HV_ND,
 	  HV_ND_GUID,
 	  .perf_device = true,
+	  .allowed_in_isolated = false,
 	},
 
 	/* PCIE */
 	{ .dev_type = HV_PCIE,
 	  HV_PCIE_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 
 	/* Synthetic Frame Buffer */
 	{ .dev_type = HV_FB,
 	  HV_SYNTHVID_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 
 	/* Synthetic Keyboard */
 	{ .dev_type = HV_KBD,
 	  HV_KBD_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 
 	/* Synthetic MOUSE */
 	{ .dev_type = HV_MOUSE,
 	  HV_MOUSE_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 
 	/* KVP */
 	{ .dev_type = HV_KVP,
 	  HV_KVP_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 
 	/* Time Synch */
 	{ .dev_type = HV_TS,
 	  HV_TS_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = true,
 	},
 
 	/* Heartbeat */
 	{ .dev_type = HV_HB,
 	  HV_HEART_BEAT_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = true,
 	},
 
 	/* Shutdown */
 	{ .dev_type = HV_SHUTDOWN,
 	  HV_SHUTDOWN_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = true,
 	},
 
 	/* File copy */
 	{ .dev_type = HV_FCOPY,
 	  HV_FCOPY_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 
 	/* Backup */
 	{ .dev_type = HV_BACKUP,
 	  HV_VSS_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 
 	/* Dynamic Memory */
 	{ .dev_type = HV_DM,
 	  HV_DM_GUID,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 
 	/* Unknown GUID */
 	{ .dev_type = HV_UNKNOWN,
 	  .perf_device = false,
+	  .allowed_in_isolated = false,
 	},
 };
 
@@ -903,6 +920,20 @@ find_primary_channel_by_offer(const struct vmbus_channel_offer_channel *offer)
 	return channel;
 }
 
+static bool vmbus_is_valid_device(const guid_t *guid)
+{
+	u16 i;
+
+	if (!hv_is_isolation_supported())
+		return true;
+
+	for (i = 0; i < ARRAY_SIZE(vmbus_devs); i++) {
+		if (guid_equal(guid, &vmbus_devs[i].guid))
+			return vmbus_devs[i].allowed_in_isolated;
+	}
+	return false;
+}
+
 /*
  * vmbus_onoffer - Handler for channel offers from vmbus in parent partition.
  *
@@ -917,6 +948,11 @@ static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
 
 	trace_vmbus_onoffer(offer);
 
+	if (!vmbus_is_valid_device(&offer->offer.if_type)) {
+		atomic_dec(&vmbus_connection.offer_in_progress);
+		return;
+	}
+
 	oldchannel = find_primary_channel_by_offer(offer);
 
 	if (oldchannel != NULL) {
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index f0d48a368f131..e3426f8c12db9 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -789,6 +789,7 @@ struct vmbus_device {
 	u16  dev_type;
 	guid_t guid;
 	bool perf_device;
+	bool allowed_in_isolated;
 };
 
 #define VMBUS_DEFAULT_MAX_PKT_SIZE 4096
-- 
2.25.1