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xen/privcmd: add IOCTL_PRIVCMD_RESTRICT
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The purpose if this ioctl is to allow a user of privcmd to restrict its
operation such that it will no longer service arbitrary hypercalls via
IOCTL_PRIVCMD_HYPERCALL, and will check for a matching domid when
servicing IOCTL_PRIVCMD_DM_OP or IOCTL_PRIVCMD_MMAP*. The aim of this
is to limit the attack surface for a compromised device model.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Paul Durrant authored and Boris Ostrovsky committed Feb 14, 2017
1 parent ab520be commit 4610d24
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Showing 2 changed files with 81 additions and 9 deletions.
88 changes: 79 additions & 9 deletions drivers/xen/privcmd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -56,16 +56,25 @@ module_param_named(dm_op_buf_max_size, privcmd_dm_op_buf_max_size, uint,
MODULE_PARM_DESC(dm_op_buf_max_size,
"Maximum size of a dm_op hypercall buffer");

struct privcmd_data {
domid_t domid;
};

static int privcmd_vma_range_is_mapped(
struct vm_area_struct *vma,
unsigned long addr,
unsigned long nr_pages);

static long privcmd_ioctl_hypercall(void __user *udata)
static long privcmd_ioctl_hypercall(struct file *file, void __user *udata)
{
struct privcmd_data *data = file->private_data;
struct privcmd_hypercall hypercall;
long ret;

/* Disallow arbitrary hypercalls if restricted */
if (data->domid != DOMID_INVALID)
return -EPERM;

if (copy_from_user(&hypercall, udata, sizeof(hypercall)))
return -EFAULT;

Expand Down Expand Up @@ -242,8 +251,9 @@ static int mmap_gfn_range(void *data, void *state)
return 0;
}

static long privcmd_ioctl_mmap(void __user *udata)
static long privcmd_ioctl_mmap(struct file *file, void __user *udata)
{
struct privcmd_data *data = file->private_data;
struct privcmd_mmap mmapcmd;
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
Expand All @@ -258,6 +268,10 @@ static long privcmd_ioctl_mmap(void __user *udata)
if (copy_from_user(&mmapcmd, udata, sizeof(mmapcmd)))
return -EFAULT;

/* If restriction is in place, check the domid matches */
if (data->domid != DOMID_INVALID && data->domid != mmapcmd.dom)
return -EPERM;

rc = gather_array(&pagelist,
mmapcmd.num, sizeof(struct privcmd_mmap_entry),
mmapcmd.entry);
Expand Down Expand Up @@ -429,8 +443,10 @@ static int alloc_empty_pages(struct vm_area_struct *vma, int numpgs)

static const struct vm_operations_struct privcmd_vm_ops;

static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
static long privcmd_ioctl_mmap_batch(
struct file *file, void __user *udata, int version)
{
struct privcmd_data *data = file->private_data;
int ret;
struct privcmd_mmapbatch_v2 m;
struct mm_struct *mm = current->mm;
Expand Down Expand Up @@ -459,6 +475,10 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
return -EINVAL;
}

/* If restriction is in place, check the domid matches */
if (data->domid != DOMID_INVALID && data->domid != m.dom)
return -EPERM;

nr_pages = DIV_ROUND_UP(m.num, XEN_PFN_PER_PAGE);
if ((m.num <= 0) || (nr_pages > (LONG_MAX >> PAGE_SHIFT)))
return -EINVAL;
Expand Down Expand Up @@ -603,8 +623,9 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
}
}

static long privcmd_ioctl_dm_op(void __user *udata)
static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
{
struct privcmd_data *data = file->private_data;
struct privcmd_dm_op kdata;
struct privcmd_dm_op_buf *kbufs;
unsigned int nr_pages = 0;
Expand All @@ -616,6 +637,10 @@ static long privcmd_ioctl_dm_op(void __user *udata)
if (copy_from_user(&kdata, udata, sizeof(kdata)))
return -EFAULT;

/* If restriction is in place, check the domid matches */
if (data->domid != DOMID_INVALID && data->domid != kdata.dom)
return -EPERM;

if (kdata.num == 0)
return 0;

Expand Down Expand Up @@ -683,6 +708,23 @@ static long privcmd_ioctl_dm_op(void __user *udata)
return rc;
}

static long privcmd_ioctl_restrict(struct file *file, void __user *udata)
{
struct privcmd_data *data = file->private_data;
domid_t dom;

if (copy_from_user(&dom, udata, sizeof(dom)))
return -EFAULT;

/* Set restriction to the specified domain, or check it matches */
if (data->domid == DOMID_INVALID)
data->domid = dom;
else if (data->domid != dom)
return -EINVAL;

return 0;
}

static long privcmd_ioctl(struct file *file,
unsigned int cmd, unsigned long data)
{
Expand All @@ -691,23 +733,27 @@ static long privcmd_ioctl(struct file *file,

switch (cmd) {
case IOCTL_PRIVCMD_HYPERCALL:
ret = privcmd_ioctl_hypercall(udata);
ret = privcmd_ioctl_hypercall(file, udata);
break;

case IOCTL_PRIVCMD_MMAP:
ret = privcmd_ioctl_mmap(udata);
ret = privcmd_ioctl_mmap(file, udata);
break;

case IOCTL_PRIVCMD_MMAPBATCH:
ret = privcmd_ioctl_mmap_batch(udata, 1);
ret = privcmd_ioctl_mmap_batch(file, udata, 1);
break;

case IOCTL_PRIVCMD_MMAPBATCH_V2:
ret = privcmd_ioctl_mmap_batch(udata, 2);
ret = privcmd_ioctl_mmap_batch(file, udata, 2);
break;

case IOCTL_PRIVCMD_DM_OP:
ret = privcmd_ioctl_dm_op(udata);
ret = privcmd_ioctl_dm_op(file, udata);
break;

case IOCTL_PRIVCMD_RESTRICT:
ret = privcmd_ioctl_restrict(file, udata);
break;

default:
Expand All @@ -717,6 +763,28 @@ static long privcmd_ioctl(struct file *file,
return ret;
}

static int privcmd_open(struct inode *ino, struct file *file)
{
struct privcmd_data *data = kzalloc(sizeof(*data), GFP_KERNEL);

if (!data)
return -ENOMEM;

/* DOMID_INVALID implies no restriction */
data->domid = DOMID_INVALID;

file->private_data = data;
return 0;
}

static int privcmd_release(struct inode *ino, struct file *file)
{
struct privcmd_data *data = file->private_data;

kfree(data);
return 0;
}

static void privcmd_close(struct vm_area_struct *vma)
{
struct page **pages = vma->vm_private_data;
Expand Down Expand Up @@ -785,6 +853,8 @@ static int privcmd_vma_range_is_mapped(
const struct file_operations xen_privcmd_fops = {
.owner = THIS_MODULE,
.unlocked_ioctl = privcmd_ioctl,
.open = privcmd_open,
.release = privcmd_release,
.mmap = privcmd_mmap,
};
EXPORT_SYMBOL_GPL(xen_privcmd_fops);
Expand Down
2 changes: 2 additions & 0 deletions include/uapi/xen/privcmd.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -111,5 +111,7 @@ struct privcmd_dm_op {
_IOC(_IOC_NONE, 'P', 4, sizeof(struct privcmd_mmapbatch_v2))
#define IOCTL_PRIVCMD_DM_OP \
_IOC(_IOC_NONE, 'P', 5, sizeof(struct privcmd_dm_op))
#define IOCTL_PRIVCMD_RESTRICT \
_IOC(_IOC_NONE, 'P', 6, sizeof(domid_t))

#endif /* __LINUX_PUBLIC_PRIVCMD_H__ */

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