Fix: OOT lttng-statedump tracepoints not visible with signed kernels

Users have reported being unable to trace non-signed modules loaded
within a kernel supporting module signature.

Here is the relevant report of this issue to Linux upstream, with a
proposed fix: https://lkml.org/lkml/2014/2/10/747

Work-around the issue for lttng-statedump.ko tracepoints.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/lttng-statedump-impl.c b/lttng-statedump-impl.c
index 0a0d1eb624e1b8f2e41f55141e57b955062211a1..7f903a71f1d3d74b1795ff99c2204ed7653d44a2 100755 (executable)
--- a/lttng-statedump-impl.c
+++ b/lttng-statedump-impl.c
@@ -50,6 +50,7 @@
 #include "wrapper/irqdesc.h"
 #include "wrapper/spinlock.h"
 #include "wrapper/fdtable.h"
+#include "wrapper/tracepoint.h"
 
 #ifdef CONFIG_GENERIC_HARDIRQS
 #include <linux/irq.h>
@@ -423,6 +424,14 @@ int lttng_statedump_start(struct lttng_session *session)
 }
 EXPORT_SYMBOL_GPL(lttng_statedump_start);
 
+static
+int __init lttng_statedump_init(void)
+{
+       return wrapper_lttng_fixup_sig(THIS_MODULE);
+}
+
+module_init(lttng_statedump_init);
+
 MODULE_LICENSE("GPL and additional rights");
 MODULE_AUTHOR("Jean-Hugues Deschenes");
 MODULE_DESCRIPTION("Linux Trace Toolkit Next Generation Statedump");

diff --git a/wrapper/tracepoint.h b/wrapper/tracepoint.h
index 798d785b1accc1ae2a703e509c6aa322aeb76860..60b36856e724e9b04125e6ef0970ed17939c4a63 100644 (file)
--- a/wrapper/tracepoint.h
+++ b/wrapper/tracepoint.h
@@ -25,6 +25,7 @@
 
 #include <linux/version.h>
 #include <linux/tracepoint.h>
+#include <linux/module.h>
 
 #if (LINUX_VERSION_CODE < KERNEL_VERSION(2,6,35))
 
@@ -41,4 +42,55 @@
 
 #endif /* HAVE_KABI_2635_TRACEPOINT */
 
+#ifdef CONFIG_MODULE_SIG
+
+#include <linux/kallsyms.h>
+#include "kallsyms.h"
+
+static inline
+int wrapper_tracepoint_module_notify(struct notifier_block *nb,
+               unsigned long val, struct module *mod)
+{
+       int (*tracepoint_module_notify_sym)(struct notifier_block *nb,
+                       unsigned long val, struct module *mod);
+
+       tracepoint_module_notify_sym =
+               (void *) kallsyms_lookup_funcptr("tracepoint_module_notify");
+       if (tracepoint_module_notify_sym) {
+               return tracepoint_module_notify_sym(nb, val, mod);
+       } else {
+               printk(KERN_WARNING "LTTng: tracepoint_module_notify symbol lookup failed.\n");
+               return -ENOSYS;
+       }
+}
+
+static inline
+int wrapper_lttng_fixup_sig(struct module *mod)
+{
+       int ret = 0;
+
+       /*
+        * This is for module.c confusing force loaded modules with
+        * unsigned modules.
+        */
+       if (!THIS_MODULE->sig_ok &&
+                       THIS_MODULE->taints & (1U << TAINT_FORCED_MODULE)) {
+               THIS_MODULE->taints &= ~(1U << TAINT_FORCED_MODULE);
+               ret = wrapper_tracepoint_module_notify(NULL,
+                               MODULE_STATE_COMING, mod);
+               THIS_MODULE->taints |= (1U << TAINT_FORCED_MODULE);
+       }
+       return ret;
+}
+
+#else /* CONFIG_MODULE_SIG */
+
+static inline
+int wrapper_lttng_fixup_sig(struct module *mod)
+{
+       return 0;
+}
+
+#endif /* #else CONFIG_MODULE_SIG */
+
 #endif /* _LTTNG_WRAPPER_TRACEPOINT_H */