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BACKPORT: ftrace: Introduce PERMANENT ftrace_ops flag

Browse source 
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>
Change-Id: Id2f8f2048541715ea66e0ac742e257fbff945e8b
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Sorayukii <sorayukii69@gmail.com>
This commit is contained in:
Miroslav Benes 2019-10-16 13:33:13 +02:00 • committed by Sorayukii
commit d9fbeaed58
3 changed files with 27 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

4
include/linux/ftrace.h
View file

@ -117,6 +117,9 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
* for any of the functions that this ops will be registered for, then
* this ops will fail to register or set_filter_ip.
* 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.
* PERMANENT - Set when the ops is permanent and should not be affected by
* ftrace_enabled.
*/
enum {
FTRACE_OPS_FL_ENABLED = 1 << 0,
@ -135,6 +138,7 @@ enum {
FTRACE_OPS_FL_IPMODIFY = 1 << 13,
FTRACE_OPS_FL_PID = 1 << 14,
FTRACE_OPS_FL_RCU = 1 << 15,
FTRACE_OPS_FL_PERMANENT = 1 << 16,
};
#ifdef CONFIG_DYNAMIC_FTRACE

3
kernel/livepatch/core.c
View file

@ -407,7 +407,8 @@ static int klp_enable_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);

23
kernel/trace/ftrace.c
View file

@ -407,6 +407,8 @@ static 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;
@ -5721,6 +5723,18 @@ 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,
@ -5738,8 +5752,6 @@ 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 */
@ -5749,12 +5761,19 @@ 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;