Livepatch uses ftrace for redirection to new patched functions. It means
that if ftrace is disabled, all live patched functions are disabled as
well. Toggling global 'ftrace_enabled' sysctl thus affect it directly.
It is not a problem per se, because only administrator can set sysctl
values, but it still may be surprising.
Introduce PERMANENT ftrace_ops flag to amend this. If the
FTRACE_OPS_FL_PERMANENT is set on any ftrace ops, the tracing cannot be
disabled by disabling ftrace_enabled. Equally, a callback with the flag
set cannot be registered if ftrace_enabled is disabled.
Link: http://lkml.kernel.org/r/20191016113316.13415-2-mbenes@suse.cz
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
a callback may be executed and RCU synchronization will not protect
it.
+FTRACE_OPS_FL_PERMANENT
+ If this is set on any ftrace ops, then the tracing cannot disabled by
+ writing 0 to the proc sysctl ftrace_enabled. Equally, a callback with
+ the flag set cannot be registered if ftrace_enabled is 0.
+
+ Livepatch uses it not to lose the function redirection, so the system
+ stays protected.
+
Filtering which functions to trace
==================================
function tracer. By default it is enabled (when function tracing is
enabled in the kernel). If it is disabled, all function tracing is
disabled. This includes not only the function tracers for ftrace, but
-also for any other uses (perf, kprobes, stack tracing, profiling, etc).
+also for any other uses (perf, kprobes, stack tracing, profiling, etc). It
+cannot be disabled if there is a callback with FTRACE_OPS_FL_PERMANENT set
+registered.
Please disable this with care.
* PID - Is affected by set_ftrace_pid (allows filtering on those pids)
* RCU - Set when the ops can only be called when RCU is watching.
* TRACE_ARRAY - The ops->private points to a trace_array descriptor.
+ * PERMANENT - Set when the ops is permanent and should not be affected by
+ * ftrace_enabled.
*/
enum {
FTRACE_OPS_FL_ENABLED = 1 << 0,
FTRACE_OPS_FL_PID = 1 << 13,
FTRACE_OPS_FL_RCU = 1 << 14,
FTRACE_OPS_FL_TRACE_ARRAY = 1 << 15,
+ FTRACE_OPS_FL_PERMANENT = 1 << 16,
};
#ifdef CONFIG_DYNAMIC_FTRACE
ops->fops.func = klp_ftrace_handler;
ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
FTRACE_OPS_FL_DYNAMIC |
- FTRACE_OPS_FL_IPMODIFY;
+ FTRACE_OPS_FL_IPMODIFY |
+ FTRACE_OPS_FL_PERMANENT;
list_add(&ops->node, &klp_ops);
if (ops->flags & FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED)
ops->flags |= FTRACE_OPS_FL_SAVE_REGS;
#endif
+ if (!ftrace_enabled && (ops->flags & FTRACE_OPS_FL_PERMANENT))
+ return -EBUSY;
if (!core_kernel_data((unsigned long)ops))
ops->flags |= FTRACE_OPS_FL_DYNAMIC;
}
EXPORT_SYMBOL_GPL(unregister_ftrace_function);
+static bool is_permanent_ops_registered(void)
+{
+ struct ftrace_ops *op;
+
+ do_for_each_ftrace_op(op, ftrace_ops_list) {
+ if (op->flags & FTRACE_OPS_FL_PERMANENT)
+ return true;
+ } while_for_each_ftrace_op(op);
+
+ return false;
+}
+
int
ftrace_enable_sysctl(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
if (ret || !write || (last_ftrace_enabled == !!ftrace_enabled))
goto out;
- last_ftrace_enabled = !!ftrace_enabled;
-
if (ftrace_enabled) {
/* we are starting ftrace again */
ftrace_startup_sysctl();
} else {
+ if (is_permanent_ops_registered()) {
+ ftrace_enabled = true;
+ ret = -EBUSY;
+ goto out;
+ }
+
/* stopping ftrace calls (just send to ftrace_stub) */
ftrace_trace_function = ftrace_stub;
ftrace_shutdown_sysctl();
}
+ last_ftrace_enabled = !!ftrace_enabled;
out:
mutex_unlock(&ftrace_lock);
return ret;