xen: add sysfs node for hypervisor build id

For support of Xen hypervisor live patching the hypervisor build id is
needed. Add a node /sys/hypervisor/properties/buildid containing the
information.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

2 files changed, 38 insertions, 1 deletions

diff --git a/Documentation/ABI/testing/sysfs-hypervisor-xen b/Documentation/ABI/testing/sysfs-hypervisor-xen
index c0edb3fdd6eb..53b7b2ea7515 100644
--- a/Documentation/ABI/testing/sysfs-hypervisor-xen
+++ b/Documentation/ABI/testing/sysfs-hypervisor-xen
@@ -1,5 +1,5 @@
 What:           /sys/hypervisor/guest_type
-Date:           May 2017
+Date:           June 2017
 KernelVersion:  4.13
 Contact:        xen-devel@lists.xenproject.org
 Description:    If running under Xen:
@@ -32,3 +32,12 @@ Description:	If running under Xen:
                 Describes Xen PMU features (as an integer). A set bit indicates
                 that the corresponding feature is enabled. See
                 include/xen/interface/xenpmu.h for available features
+
+What:           /sys/hypervisor/properties/buildid
+Date:           June 2017
+KernelVersion:  4.13
+Contact:        xen-devel@lists.xenproject.org
+Description:    If running under Xen:
+                Build id of the hypervisor, needed for hypervisor live patching.
+                Might return "<denied>" in case of special security settings
+                in the hypervisor.
diff --git a/drivers/xen/sys-hypervisor.c b/drivers/xen/sys-hypervisor.c
index 2f78f84a31e9..9d314bba7c4e 100644
--- a/drivers/xen/sys-hypervisor.c
+++ b/drivers/xen/sys-hypervisor.c
@@ -356,12 +356,40 @@ static ssize_t features_show(struct hyp_sysfs_attr *attr, char *buffer)
 
 HYPERVISOR_ATTR_RO(features);
 
+static ssize_t buildid_show(struct hyp_sysfs_attr *attr, char *buffer)
+{
+        ssize_t ret;
+        struct xen_build_id *buildid;
+
+        ret = HYPERVISOR_xen_version(XENVER_build_id, NULL);
+        if (ret < 0) {
+                if (ret == -EPERM)
+                        ret = sprintf(buffer, "<denied>");
+                return ret;
+        }
+
+        buildid = kmalloc(sizeof(*buildid) + ret, GFP_KERNEL);
+        if (!buildid)
+                return -ENOMEM;
+
+        buildid->len = ret;
+        ret = HYPERVISOR_xen_version(XENVER_build_id, buildid);
+        if (ret > 0)
+                ret = sprintf(buffer, "%s", buildid->buf);
+        kfree(buildid);
+
+        return ret;
+}
+
+HYPERVISOR_ATTR_RO(buildid);
+
 static struct attribute *xen_properties_attrs[] = {
         &capabilities_attr.attr,
         &changeset_attr.attr,
         &virtual_start_attr.attr,
         &pagesize_attr.attr,
         &features_attr.attr,
+        &buildid_attr.attr,
         NULL
 };