livepatch: introduce shadow variable API

[linux-2.6-microblaze.git] / samples / livepatch / livepatch-shadow-fix2.c

diff --git a/samples/livepatch/livepatch-shadow-fix2.c b/samples/livepatch/livepatch-shadow-fix2.c
new file mode 100644 (file)
index 0000000..53c1794
--- /dev/null
+++ b/samples/livepatch/livepatch-shadow-fix2.c
@@ -0,0 +1,168 @@
+/*
+ * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * livepatch-shadow-fix2.c - Shadow variables, livepatch demo
+ *
+ * Purpose
+ * -------
+ *
+ * Adds functionality to livepatch-shadow-mod's in-flight data
+ * structures through a shadow variable.  The livepatch patches a
+ * routine that periodically inspects data structures, incrementing a
+ * per-data-structure counter, creating the counter if needed.
+ *
+ *
+ * Usage
+ * -----
+ *
+ * This module is not intended to be standalone.  See the "Usage"
+ * section of livepatch-shadow-mod.c.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/livepatch.h>
+#include <linux/slab.h>
+
+/* Shadow variable enums */
+#define SV_LEAK                1
+#define SV_COUNTER     2
+
+struct dummy {
+       struct list_head list;
+       unsigned long jiffies_expire;
+};
+
+bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
+{
+       int *shadow_count;
+       int count;
+
+       /*
+        * Patch: handle in-flight dummy structures, if they do not
+        * already have a SV_COUNTER shadow variable, then attach a
+        * new one.
+        */
+       count = 0;
+       shadow_count = klp_shadow_get_or_alloc(d, SV_COUNTER,
+                                              &count, sizeof(count),
+                                              GFP_NOWAIT);
+       if (shadow_count)
+               *shadow_count += 1;
+
+       return time_after(jiffies, d->jiffies_expire);
+}
+
+void livepatch_fix2_dummy_free(struct dummy *d)
+{
+       void **shadow_leak, *leak;
+       int *shadow_count;
+
+       /* Patch: copy the memory leak patch from the fix1 module. */
+       shadow_leak = klp_shadow_get(d, SV_LEAK);
+       if (shadow_leak) {
+               leak = *shadow_leak;
+               klp_shadow_free(d, SV_LEAK);
+               kfree(leak);
+               pr_info("%s: dummy @ %p, prevented leak @ %p\n",
+                        __func__, d, leak);
+       } else {
+               pr_info("%s: dummy @ %p leaked!\n", __func__, d);
+       }
+
+       /*
+        * Patch: fetch the SV_COUNTER shadow variable and display
+        * the final count.  Detach the shadow variable.
+        */
+       shadow_count = klp_shadow_get(d, SV_COUNTER);
+       if (shadow_count) {
+               pr_info("%s: dummy @ %p, check counter = %d\n",
+                       __func__, d, *shadow_count);
+               klp_shadow_free(d, SV_COUNTER);
+       }
+
+       kfree(d);
+}
+
+static struct klp_func funcs[] = {
+       {
+               .old_name = "dummy_check",
+               .new_func = livepatch_fix2_dummy_check,
+       },
+       {
+               .old_name = "dummy_free",
+               .new_func = livepatch_fix2_dummy_free,
+       }, { }
+};
+
+static struct klp_object objs[] = {
+       {
+               .name = "livepatch_shadow_mod",
+               .funcs = funcs,
+       }, { }
+};
+
+static struct klp_patch patch = {
+       .mod = THIS_MODULE,
+       .objs = objs,
+};
+
+static int livepatch_shadow_fix2_init(void)
+{
+       int ret;
+
+       if (!klp_have_reliable_stack() && !patch.immediate) {
+               /*
+                * WARNING: Be very careful when using 'patch.immediate' in
+                * your patches.  It's ok to use it for simple patches like
+                * this, but for more complex patches which change function
+                * semantics, locking semantics, or data structures, it may not
+                * be safe.  Use of this option will also prevent removal of
+                * the patch.
+                *
+                * See Documentation/livepatch/livepatch.txt for more details.
+                */
+               patch.immediate = true;
+               pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");
+       }
+
+       ret = klp_register_patch(&patch);
+       if (ret)
+               return ret;
+       ret = klp_enable_patch(&patch);
+       if (ret) {
+               WARN_ON(klp_unregister_patch(&patch));
+               return ret;
+       }
+       return 0;
+}
+
+static void livepatch_shadow_fix2_exit(void)
+{
+       /* Cleanup any existing SV_COUNTER shadow variables */
+       klp_shadow_free_all(SV_COUNTER);
+
+       WARN_ON(klp_unregister_patch(&patch));
+}
+
+module_init(livepatch_shadow_fix2_init);
+module_exit(livepatch_shadow_fix2_exit);
+MODULE_LICENSE("GPL");
+MODULE_INFO(livepatch, "Y");