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ftrace: Introduce PERMANENT ftrace_ops flag

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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>
This commit is contained in:
Miroslav Benes
2019-10-16 13:33:13 +02:00
committed by Steven Rostedt
parent a99d8080aa
commit 7162431dcf
5 changed files with 37 additions and 4 deletions
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3
kernel/livepatch/patch.c
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@@ -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);