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, 119 insertions, 0 deletions

diff --git a/tools/objtool/klp-symid.c b/tools/objtool/klp-symid.c
new file mode 100644
index 000000000..b19f76dff
--- /dev/null
+++ b/tools/objtool/klp-symid.c
@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Emit the .klp.symid table which allows "objtool klp diff" to reliably
+ * disambiguate duplicate-named local symbols in vmlinux.
+ *
+ * Livepatch identifies a duplicate-named symbol by its position (sympos)
+ * among the same-named kallsyms entries, counted in ascending address order
+ * in the final linked vmlinux.  That order can't be derived from vmlinux.o
+ * alone: the final link reorders sub-sections (.text.unlikely*, .data..*,
+ * etc).
+ *
+ * Bridge the gap with a table which survives the final link: a single
+ * non-alloc section containing an array of { id, addr } entries, where
+ * 'id' is a unique counter identifier and 'addr' has a relocation to the
+ * symbol.  The linker copies 'id' verbatim and resolves 'addr' to the symbol's
+ * final address.
+ *
+ * The table is only emitted for vmlinux.o, and only when klp-build asks for it
+ * with KLP_SYMIDS=1, which adds --klp-symids to the vmlinux.o objtool run.
+ *
+ * It can't survive --gc-sections, which sweeps the whole section; klp-build
+ * rejects CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.
+ */
+#include <linux/string.h>
+
+#include <objtool/objtool.h>
+#include <objtool/warn.h>
+#include <objtool/endianness.h>
+#include <objtool/klp.h>
+
+static const char * const discarded_secs[] = {
+	".discard",
+	".exitcall.exit",
+	".modinfo",
+	".no_trim_symbol",
+	"__tracepoint_check",
+};
+
+static bool discarded_sec(struct section *sec)
+{
+	if (!(sec->sh.sh_flags & SHF_ALLOC))
+		return true;
+
+	for (int i = 0; i < ARRAY_SIZE(discarded_secs); i++)
+		if (strstarts(sec->name, discarded_secs[i]))
+			return true;
+
+	return false;
+}
+
+static bool symid_needed(struct elf *elf, struct symbol *sym)
+{
+	struct symbol *s;
+
+	if (!is_local_sym(sym) || is_undef_sym(sym))
+		return false;
+
+	if (!is_func_sym(sym) && !is_object_sym(sym))
+		return false;
+
+	if (is_prefix_func(sym))
+		return false;
+
+	if (discarded_sec(sym->sec))
+		return false;
+
+	for_each_sym_by_name(elf, sym->name, s) {
+		if (s == sym || is_sec_sym(s) || is_file_sym(s) || is_undef_sym(s))
+			continue;
+		return true;
+	}
+
+	return false;
+}
+
+int klp_create_symid_sections(struct objtool_file *file)
+{
+	struct elf *elf = file->elf;
+	struct klp_symid *symids;
+	struct section *sec;
+	struct symbol *sym;
+	u64 nr = 0, i = 0;
+
+	if (!str_ends_with(objname, "vmlinux.o"))
+		return 0;
+
+	for_each_sym(elf, sym)
+		if (symid_needed(elf, sym))
+			nr++;
+
+	if (!nr)
+		return 0;
+
+	sec = elf_create_section(elf, KLP_SYMID_SEC, 0, sizeof(struct klp_symid),
+				 SHT_PROGBITS, 8, 0);
+	if (!sec)
+		return -1;
+
+	symids = elf_add_data(elf, sec, NULL, nr * sizeof(struct klp_symid));
+	if (!symids)
+		return -1;
+
+	for_each_sym(elf, sym) {
+		if (!symid_needed(elf, sym))
+			continue;
+
+		symids[i].id = bswap_if_needed(elf, i);
+
+		if (!elf_create_reloc(elf, sec,
+				      i * sizeof(struct klp_symid) +
+				      offsetof(struct klp_symid, addr),
+				      sym, 0, R_ABS64))
+			return -1;
+
+		i++;
+	}
+
+	return 0;
+}