linux-kernel - [PATCH v2 2/2] kvm: Device assignment permission checks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20111220143025.30073.36120.stgit@bling.home>
Date:	Tue, 20 Dec 2011 07:30:25 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	avi@...hat.com, kvm@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, jan.kiszka@...mens.com,
	levinsasha928@...il.com
Subject: [PATCH v2 2/2] kvm: Device assignment permission checks

Only allow KVM device assignment to attach to devices which:

 - Are not bridges
 - Have BAR resources (assume others are special devices)
 - The user has permissions to use

Assigning a bridge is a configuration error, it's not supported, and
typically doesn't result in the behavior the user is expecting anyway.
Devices without BAR resources are typically chipset components that
also don't have host drivers.  We don't want users to hold such devices
captive or cause system problems by fencing them off into an iommu
domain.  We determine "permission to use" by testing whether the user
has access to the PCI sysfs resource files.  By default a normal user
will not have access to these files, so it provides a good indication
that an administration agent has granted the user access to the device.

Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
---

 Documentation/virtual/kvm/api.txt |    4 +++
 virt/kvm/assigned-dev.c           |   55 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 58 insertions(+), 1 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index ee2c96b..4df9af4 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1154,6 +1154,10 @@ following flags are specified:
 The KVM_DEV_ASSIGN_ENABLE_IOMMU flag is a mandatory option to ensure
 isolation of the device.  Usages not specifying this flag are deprecated.
 
+Only PCI header type 0 devices with PCI BAR resources are supported by
+device assignment.  The user requesting this ioctl must have read/write
+access to the PCI sysfs resource files associated with the device.
+
 4.49 KVM_DEASSIGN_PCI_DEVICE
 
 Capability: KVM_CAP_DEVICE_DEASSIGNMENT
diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index a251a28..faec641 100644
--- a/virt/kvm/assigned-dev.c
+++ b/virt/kvm/assigned-dev.c
@@ -17,6 +17,7 @@
 #include <linux/pci.h>
 #include <linux/interrupt.h>
 #include <linux/slab.h>
+#include <linux/namei.h>
 #include "irq.h"
 
 static struct kvm_assigned_dev_kernel *kvm_find_assigned_dev(struct list_head *head,
@@ -483,9 +484,11 @@ out:
 static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
 				      struct kvm_assigned_pci_dev *assigned_dev)
 {
-	int r = 0, idx;
+	int r = 0, idx, i;
 	struct kvm_assigned_dev_kernel *match;
 	struct pci_dev *dev;
+	u8 header_type;
+	bool bar_found = false;
 
 	if (!(assigned_dev->flags & KVM_DEV_ASSIGN_ENABLE_IOMMU))
 		return -EINVAL;
@@ -516,6 +519,56 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
 		r = -EINVAL;
 		goto out_free;
 	}
+
+	/* Don't allow bridges to be assigned */
+	pci_read_config_byte(dev, PCI_HEADER_TYPE, &header_type);
+	if ((header_type & PCI_HEADER_TYPE) != PCI_HEADER_TYPE_NORMAL) {
+		r = -EPERM;
+		goto out_put;
+	}
+
+	/* We want to test whether the caller has been granted permissions to
+	 * use this device.  To be able to configure and control the device,
+	 * the user needs access to PCI configuration space and BAR resources.
+	 * These are accessed through PCI sysfs.  PCI config space is often
+	 * passed to the process calling this ioctl via file descriptor, so we
+	 * can't rely on access to that file.  We can check for permissions
+	 * on each of the BAR resource files, which is a pretty clear
+	 * indicator that the user has been granted access to the device. */
+	for (i = PCI_STD_RESOURCES; i <= PCI_STD_RESOURCE_END; i++) {
+		char buf[64];
+		struct path path;
+		struct inode *inode;
+
+		if (!pci_resource_len(dev, i))
+			continue;
+
+		/* Per sysfs-rules, sysfs is always at /sys */
+		snprintf(buf, sizeof(buf), "/sys/bus/pci/devices/%04x:%02x:"
+			 "%02x.%d/resource%d", pci_domain_nr(dev->bus),
+			 dev->bus->number, PCI_SLOT(dev->devfn),
+			 PCI_FUNC(dev->devfn), i);
+
+		r = kern_path(buf, LOOKUP_FOLLOW, &path);
+		if (r)
+			goto out_put;
+
+		inode = path.dentry->d_inode;
+
+		r = inode_permission(inode, MAY_READ | MAY_WRITE | MAY_ACCESS);
+		path_put(&path);
+		if (r)
+			goto out_put;
+
+		bar_found = true;
+	}
+
+	/* If no resources, probably something special */
+	if (!bar_found) {
+		r = -EPERM;
+		goto out_put;
+	}
+
 	if (pci_enable_device(dev)) {
 		printk(KERN_INFO "%s: Could not enable PCI device\n", __func__);
 		r = -EBUSY;

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/