[PATCH 2/3] xen/privcmd: Add IOCTL_PRIVCMD_DM_OP

[Paul Durrant]

Recently a new dm_op[1] hypercall was added to Xen to provide a mechanism
for restricting device emulators (such as QEMU) to a limited set of
hypervisor operations, and being able to audit those operations in the
kernel of the domain in which they run.

This patch adds IOCTL_PRIVCMD_DM_OP as gateway for __HYPERVISOR_dm_op,
bouncing the callers buffers through kernel memory to allow the address
ranges to be audited (and negating the need to bounce through locked
memory in user-space).

[1] http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=524a98c2

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
---
 arch/x86/include/asm/xen/hypercall.h |   7 ++
 drivers/xen/privcmd.c                | 122 +++++++++++++++++++++++++++++++++++
 include/uapi/xen/privcmd.h           |  13 ++++
 include/xen/interface/hvm/dm_op.h    |  32 +++++++++
 include/xen/interface/xen.h          |   1 +
 5 files changed, 175 insertions(+)
 create mode 100644 include/xen/interface/hvm/dm_op.h

diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
index a12a047..f6d20f6 100644
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -472,6 +472,13 @@ HYPERVISOR_xenpmu_op(unsigned int op, void *arg)
 	return _hypercall2(int, xenpmu_op, op, arg);
 }
 
+static inline int
+HYPERVISOR_dm_op(
+	domid_t dom, unsigned int nr_bufs, void *bufs)
+{
+	return _hypercall3(int, dm_op, dom, nr_bufs, bufs);
+}
+
 static inline void
 MULTI_fpu_taskswitch(struct multicall_entry *mcl, int set)
 {
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index b4e5e27..31c43f4 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -32,6 +32,7 @@
 #include <xen/xen.h>
 #include <xen/privcmd.h>
 #include <xen/interface/xen.h>
+#include <xen/interface/hvm/dm_op.h>
 #include <xen/features.h>
 #include <xen/page.h>
 #include <xen/xen-ops.h>
@@ -548,6 +549,123 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
 	goto out;
 }
 
+static int bounce_in(struct privcmd_dm_op_buf kbufs[], void *kptr[],
+	unsigned int num)
+{
+	unsigned int i;
+	int rc = 0;
+
+	for (i = 0; i < num; i++) {
+		kptr[i] = kzalloc(kbufs[i].size, GFP_KERNEL);
+		if (!kptr[i]) {
+			rc = -ENOMEM;
+			break;
+		}
+
+		if (copy_from_user(kptr[i], kbufs[i].uptr, kbufs[i].size)) {
+			rc = -EFAULT;
+			break;
+		}
+	}
+
+	return rc;
+}
+
+static int bounce_out(struct privcmd_dm_op_buf kbufs[], void *kptr[],
+	unsigned int num)
+{
+	unsigned int i;
+	int rc = 0;
+
+	for (i = 0; i < num; i++)
+		if (copy_to_user(kbufs[i].uptr, kptr[i], kbufs[i].size))
+			rc = -EFAULT;
+
+	return rc;
+}
+
+static void free_kptr(void *kptr[], unsigned int num)
+{
+	unsigned int i;
+
+	if (!kptr)
+		return;
+
+	for (i = 0; i < num; i++)
+		kfree(kptr[i]);
+
+	kfree(kptr);
+}
+
+static long privcmd_ioctl_dm_op(void __user *udata)
+{
+	struct privcmd_dm_op kdata;
+	struct privcmd_dm_op_buf *kbufs;
+	void **kptr = NULL;
+	struct xen_dm_op_buf *xbufs = NULL;
+	unsigned int i;
+	long rc;
+
+	if (copy_from_user(&kdata, udata, sizeof(kdata)))
+		return -EFAULT;
+
+	if (kdata.num == 0)
+		return 0;
+
+	/*
+	 * Set a tolerable upper limit on the number of buffers
+	 * without being overly restrictive, since we can't easily
+	 * predict what future dm_ops may require.
+	 */
+	if (kdata.num * sizeof(*kbufs) > PAGE_SIZE)
+		return -EINVAL;
+
+	kbufs = kcalloc(kdata.num, sizeof(*kbufs), GFP_KERNEL);
+	if (!kbufs)
+		return -ENOMEM;
+
+	if (copy_from_user(kbufs, kdata.ubufs,
+			   sizeof(*kbufs) * kdata.num)) {
+		rc = -EFAULT;
+		goto out;
+	}
+
+	kptr = kcalloc(kdata.num, sizeof(*kptr), GFP_KERNEL);
+	if (!kptr) {
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	rc = bounce_in(kbufs, kptr, kdata.num);
+	if (rc)
+		goto out;
+
+	xbufs = kcalloc(kdata.num, sizeof(*xbufs), GFP_KERNEL);
+	if (!xbufs) {
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	for (i = 0; i < kdata.num; i++) {
+		set_xen_guest_handle(xbufs[i].h, kptr[i]);
+		xbufs[i].size = kbufs[i].size;
+	}
+
+	xen_preemptible_hcall_begin();
+	rc = HYPERVISOR_dm_op(kdata.dom, kdata.num, xbufs);
+	xen_preemptible_hcall_end();
+
+	if (!rc)
+		rc = bounce_out(kbufs, kptr, kdata.num);
+
+out:
+	kfree(xbufs);
+	free_kptr(kptr, kdata.num);
+	kfree(kbufs);
+
+	return rc;
+}
+
 static long privcmd_ioctl(struct file *file,
 			  unsigned int cmd, unsigned long data)
 {
@@ -571,6 +689,10 @@ static long privcmd_ioctl(struct file *file,
 		ret = privcmd_ioctl_mmap_batch(udata, 2);
 		break;
 
+	case IOCTL_PRIVCMD_DM_OP:
+		ret = privcmd_ioctl_dm_op(udata);
+		break;
+
 	default:
 		break;
 	}
diff --git a/include/uapi/xen/privcmd.h b/include/uapi/xen/privcmd.h
index 7ddeeda..f8c5d75 100644
--- a/include/uapi/xen/privcmd.h
+++ b/include/uapi/xen/privcmd.h
@@ -77,6 +77,17 @@ struct privcmd_mmapbatch_v2 {
 	int __user *err;  /* array of error codes */
 };
 
+struct privcmd_dm_op_buf {
+	void __user *uptr;
+	size_t size;
+};
+
+struct privcmd_dm_op {
+	domid_t dom;
+	__u16 num;
+	const struct privcmd_dm_op_buf __user *ubufs;
+};
+
 /*
  * @cmd: IOCTL_PRIVCMD_HYPERCALL
  * @arg: &privcmd_hypercall_t
@@ -98,5 +109,7 @@ struct privcmd_mmapbatch_v2 {
 	_IOC(_IOC_NONE, 'P', 3, sizeof(struct privcmd_mmapbatch))
 #define IOCTL_PRIVCMD_MMAPBATCH_V2				\
 	_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))
 
 #endif /* __LINUX_PUBLIC_PRIVCMD_H__ */
diff --git a/include/xen/interface/hvm/dm_op.h b/include/xen/interface/hvm/dm_op.h
new file mode 100644
index 0000000..ee9e480
--- /dev/null
+++ b/include/xen/interface/hvm/dm_op.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2016, Citrix Systems Inc
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef __XEN_PUBLIC_HVM_DM_OP_H__
+#define __XEN_PUBLIC_HVM_DM_OP_H__
+
+struct xen_dm_op_buf {
+	GUEST_HANDLE(void) h;
+	xen_ulong_t size;
+};
+DEFINE_GUEST_HANDLE_STRUCT(xen_dm_op_buf);
+
+#endif /* __XEN_PUBLIC_HVM_DM_OP_H__ */
diff --git a/include/xen/interface/xen.h b/include/xen/interface/xen.h
index 1b0d189..4f4830e 100644
--- a/include/xen/interface/xen.h
+++ b/include/xen/interface/xen.h
@@ -81,6 +81,7 @@
 #define __HYPERVISOR_tmem_op              38
 #define __HYPERVISOR_xc_reserved_op       39 /* reserved for XenClient */
 #define __HYPERVISOR_xenpmu_op            40
+#define __HYPERVISOR_dm_op                41
 
 /* Architecture-specific hypercall definitions. */
 #define __HYPERVISOR_arch_0               48
-- 
2.1.4