ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 91 insertions, 0 deletions

diff --git a/Documentation/security/sak.rst b/Documentation/security/sak.rst
new file mode 100644
index 000000000..260e1d368
--- /dev/null
+++ b/Documentation/security/sak.rst
@@ -0,0 +1,91 @@
+=========================================
+Linux Secure Attention Key (SAK) handling
+=========================================
+
+:Date: 18 March 2001
+:Author: Andrew Morton
+
+An operating system's Secure Attention Key is a security tool which is
+provided as protection against trojan password capturing programs.  It
+is an undefeatable way of killing all programs which could be
+masquerading as login applications.  Users need to be taught to enter
+this key sequence before they log in to the system.
+
+From the PC keyboard, Linux has two similar but different ways of
+providing SAK.  One is the ALT-SYSRQ-K sequence.  You shouldn't use
+this sequence.  It is only available if the kernel was compiled with
+sysrq support.
+
+The proper way of generating a SAK is to define the key sequence using
+``loadkeys``.  This will work whether or not sysrq support is compiled
+into the kernel.
+
+SAK works correctly when the keyboard is in raw mode.  This means that
+once defined, SAK will kill a running X server.  If the system is in
+run level 5, the X server will restart.  This is what you want to
+happen.
+
+What key sequence should you use? Well, CTRL-ALT-DEL is used to reboot
+the machine.  CTRL-ALT-BACKSPACE is magical to the X server.  We'll
+choose CTRL-ALT-PAUSE.
+
+In your rc.sysinit (or rc.local) file, add the command::
+
+	echo "control alt keycode 101 = SAK" | /bin/loadkeys
+
+And that's it!  Only the superuser may reprogram the SAK key.
+
+
+.. note::
+
+  1. Linux SAK is said to be not a "true SAK" as is required by
+     systems which implement C2 level security.  This author does not
+     know why.
+
+
+  2. On the PC keyboard, SAK kills all applications which have
+     /dev/console opened.
+
+     Unfortunately this includes a number of things which you don't
+     actually want killed.  This is because these applications are
+     incorrectly holding /dev/console open.  Be sure to complain to your
+     Linux distributor about this!
+
+     You can identify processes which will be killed by SAK with the
+     command::
+
+	# ls -l /proc/[0-9]*/fd/* | grep console
+	l-wx------    1 root     root           64 Mar 18 00:46 /proc/579/fd/0 -> /dev/console
+
+     Then::
+
+	# ps aux|grep 579
+	root       579  0.0  0.1  1088  436 ?        S    00:43   0:00 gpm -t ps/2
+
+     So ``gpm`` will be killed by SAK.  This is a bug in gpm.  It should
+     be closing standard input.  You can work around this by finding the
+     initscript which launches gpm and changing it thusly:
+
+     Old::
+
+	daemon gpm
+
+     New::
+
+	daemon gpm < /dev/null
+
+     Vixie cron also seems to have this problem, and needs the same treatment.
+
+     Also, one prominent Linux distribution has the following three
+     lines in its rc.sysinit and rc scripts::
+
+	exec 3<&0
+	exec 4>&1
+	exec 5>&2
+
+     These commands cause **all** daemons which are launched by the
+     initscripts to have file descriptors 3, 4 and 5 attached to
+     /dev/console.  So SAK kills them all.  A workaround is to simply
+     delete these lines, but this may cause system management
+     applications to malfunction - test everything well.
+