From fbc872c38c8fed31948c85683b5326ee5ab9fccc Mon Sep 17 00:00:00 2001 From: David Vrabel Date: Mon, 11 Jul 2016 15:45:51 +0100 Subject: [PATCH] xen/evtchn: add IOCTL_EVTCHN_RESTRICT IOCTL_EVTCHN_RESTRICT limits the file descriptor to being able to bind to interdomain event channels from a specific domain. Event channels that are already bound continue to work for sending and receiving notifications. This is useful as part of deprivileging a user space PV backend or device model (QEMU). e.g., Once the device model as bound to the ioreq server event channels it can restrict the file handle so an exploited DM cannot use it to create or bind to arbitrary event channels. Signed-off-by: David Vrabel Reviewed-by: Boris Ostrovsky --- drivers/xen/evtchn.c | 40 +++++++++++++++++++++++++++++++++++++++ include/uapi/xen/evtchn.h | 15 +++++++++++++++ 2 files changed, 55 insertions(+) diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c index f4edd6df3df2..7efd1cb9bb40 100644 --- a/drivers/xen/evtchn.c +++ b/drivers/xen/evtchn.c @@ -73,8 +73,12 @@ struct per_user_data { wait_queue_head_t evtchn_wait; struct fasync_struct *evtchn_async_queue; const char *name; + + domid_t restrict_domid; }; +#define UNRESTRICTED_DOMID ((domid_t)-1) + struct user_evtchn { struct rb_node node; struct per_user_data *user; @@ -443,6 +447,10 @@ static long evtchn_ioctl(struct file *file, struct ioctl_evtchn_bind_virq bind; struct evtchn_bind_virq bind_virq; + rc = -EACCES; + if (u->restrict_domid != UNRESTRICTED_DOMID) + break; + rc = -EFAULT; if (copy_from_user(&bind, uarg, sizeof(bind))) break; @@ -468,6 +476,11 @@ static long evtchn_ioctl(struct file *file, if (copy_from_user(&bind, uarg, sizeof(bind))) break; + rc = -EACCES; + if (u->restrict_domid != UNRESTRICTED_DOMID && + u->restrict_domid != bind.remote_domain) + break; + bind_interdomain.remote_dom = bind.remote_domain; bind_interdomain.remote_port = bind.remote_port; rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain, @@ -485,6 +498,10 @@ static long evtchn_ioctl(struct file *file, struct ioctl_evtchn_bind_unbound_port bind; struct evtchn_alloc_unbound alloc_unbound; + rc = -EACCES; + if (u->restrict_domid != UNRESTRICTED_DOMID) + break; + rc = -EFAULT; if (copy_from_user(&bind, uarg, sizeof(bind))) break; @@ -553,6 +570,27 @@ static long evtchn_ioctl(struct file *file, break; } + case IOCTL_EVTCHN_RESTRICT_DOMID: { + struct ioctl_evtchn_restrict_domid ierd; + + rc = -EACCES; + if (u->restrict_domid != UNRESTRICTED_DOMID) + break; + + rc = -EFAULT; + if (copy_from_user(&ierd, uarg, sizeof(ierd))) + break; + + rc = -EINVAL; + if (ierd.domid == 0 || ierd.domid >= DOMID_FIRST_RESERVED) + break; + + u->restrict_domid = ierd.domid; + rc = 0; + + break; + } + default: rc = -ENOSYS; break; @@ -601,6 +639,8 @@ static int evtchn_open(struct inode *inode, struct file *filp) mutex_init(&u->ring_cons_mutex); spin_lock_init(&u->ring_prod_lock); + u->restrict_domid = UNRESTRICTED_DOMID; + filp->private_data = u; return nonseekable_open(inode, filp); diff --git a/include/uapi/xen/evtchn.h b/include/uapi/xen/evtchn.h index 14e833ee4e0b..cb4aa4bb905e 100644 --- a/include/uapi/xen/evtchn.h +++ b/include/uapi/xen/evtchn.h @@ -85,4 +85,19 @@ struct ioctl_evtchn_notify { #define IOCTL_EVTCHN_RESET \ _IOC(_IOC_NONE, 'E', 5, 0) +/* + * Restrict this file descriptor so that it can only be used to bind + * new interdomain events from one domain. + * + * Once a file descriptor has been restricted it cannot be + * de-restricted, and must be closed and re-opened. Event channels + * which were bound before restricting remain bound afterwards, and + * can be notified as usual. + */ +#define IOCTL_EVTCHN_RESTRICT_DOMID \ + _IOC(_IOC_NONE, 'E', 6, sizeof(struct ioctl_evtchn_restrict_domid)) +struct ioctl_evtchn_restrict_domid { + domid_t domid; +}; + #endif /* __LINUX_PUBLIC_EVTCHN_H__ */ -- GitLab