From 7162431dcf72032835d369c8d7b51311df407938 Mon Sep 17 00:00:00 2001 From: Miroslav Benes Date: Wed, 16 Oct 2019 13:33:13 +0200 Subject: [PATCH] ftrace: Introduce PERMANENT ftrace_ops flag 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 Reviewed-by: Kamalesh Babulal Signed-off-by: Miroslav Benes Signed-off-by: Steven Rostedt (VMware) --- Documentation/trace/ftrace-uses.rst | 8 ++++++++ Documentation/trace/ftrace.rst | 4 +++- include/linux/ftrace.h | 3 +++ kernel/livepatch/patch.c | 3 ++- kernel/trace/ftrace.c | 23 +++++++++++++++++++++-- 5 files changed, 37 insertions(+), 4 deletions(-) diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst index 1fbc698..740bd02 100644 --- a/Documentation/trace/ftrace-uses.rst +++ b/Documentation/trace/ftrace-uses.rst @@ -170,6 +170,14 @@ FTRACE_OPS_FL_RCU 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 ================================== diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index e3060ee..d2b5657 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -2976,7 +2976,9 @@ Note, the proc sysctl ftrace_enable is a big on/off switch for the 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. diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index 8a8cb3c..8385caf 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -142,6 +142,8 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops); * 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, @@ -160,6 +162,7 @@ enum { 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 diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c index bd43537..b552cf2 100644 --- a/kernel/livepatch/patch.c +++ b/kernel/livepatch/patch.c @@ -196,7 +196,8 @@ static int klp_patch_func(struct klp_func *func) 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); diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index f296d89..89e9128 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -326,6 +326,8 @@ int __register_ftrace_function(struct ftrace_ops *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; @@ -6754,6 +6756,18 @@ int unregister_ftrace_function(struct ftrace_ops *ops) } 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, @@ -6771,8 +6785,6 @@ ftrace_enable_sysctl(struct ctl_table *table, int write, if (ret || !write || (last_ftrace_enabled == !!ftrace_enabled)) goto out; - last_ftrace_enabled = !!ftrace_enabled; - if (ftrace_enabled) { /* we are starting ftrace again */ @@ -6783,12 +6795,19 @@ ftrace_enable_sysctl(struct ctl_table *table, int write, 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; -- 2.7.4