[RFC][PATCH 3/4] kprobes: Allow kprobes with CONFIG_MODULES=n

[Calvin Owens <jcalvinowens@gmail.com>]

If something like this is merged down the road, it can go in at leisure
once the module_alloc change is in: it's a one-way dependency.

Signed-off-by: Calvin Owens <jcalvinowens@gmail.com>
---
 arch/Kconfig                |  2 +-
 kernel/kprobes.c            | 22 ++++++++++++++++++++++
 kernel/trace/trace_kprobe.c | 11 +++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index cfc24ced16dd..e60ce984d095 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -52,8 +52,8 @@ config GENERIC_ENTRY
 
 config KPROBES
 	bool "Kprobes"
-	depends on MODULES
 	depends on HAVE_KPROBES
+	select MODULE_ALLOC
 	select KALLSYMS
 	select TASKS_RCU if PREEMPTION
 	help
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 9d9095e81792..194270e17d57 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1556,8 +1556,12 @@ static bool is_cfi_preamble_symbol(unsigned long addr)
 		str_has_prefix("__pfx_", symbuf);
 }
 
+#if IS_ENABLED(CONFIG_MODULES)
 static int check_kprobe_address_safe(struct kprobe *p,
 				     struct module **probed_mod)
+#else
+static int check_kprobe_address_safe(struct kprobe *p)
+#endif
 {
 	int ret;
 
@@ -1580,6 +1584,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
 		goto out;
 	}
 
+#if IS_ENABLED(CONFIG_MODULES)
 	/* Check if 'p' is probing a module. */
 	*probed_mod = __module_text_address((unsigned long) p->addr);
 	if (*probed_mod) {
@@ -1603,6 +1608,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
 			ret = -ENOENT;
 		}
 	}
+#endif
+
 out:
 	preempt_enable();
 	jump_label_unlock();
@@ -1614,7 +1621,9 @@ int register_kprobe(struct kprobe *p)
 {
 	int ret;
 	struct kprobe *old_p;
+#if IS_ENABLED(CONFIG_MODULES)
 	struct module *probed_mod;
+#endif
 	kprobe_opcode_t *addr;
 	bool on_func_entry;
 
@@ -1633,7 +1642,11 @@ int register_kprobe(struct kprobe *p)
 	p->nmissed = 0;
 	INIT_LIST_HEAD(&p->list);
 
+#if IS_ENABLED(CONFIG_MODULES)
 	ret = check_kprobe_address_safe(p, &probed_mod);
+#else
+	ret = check_kprobe_address_safe(p);
+#endif
 	if (ret)
 		return ret;
 
@@ -1676,8 +1689,10 @@ int register_kprobe(struct kprobe *p)
 out:
 	mutex_unlock(&kprobe_mutex);
 
+#if IS_ENABLED(CONFIG_MODULES)
 	if (probed_mod)
 		module_put(probed_mod);
+#endif
 
 	return ret;
 }
@@ -2482,6 +2497,7 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
 	return 0;
 }
 
+#if IS_ENABLED(CONFIG_MODULES)
 /* Remove all symbols in given area from kprobe blacklist */
 static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
 {
@@ -2499,6 +2515,7 @@ static void kprobe_remove_ksym_blacklist(unsigned long entry)
 {
 	kprobe_remove_area_blacklist(entry, entry + 1);
 }
+#endif
 
 int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
 				   char *type, char *sym)
@@ -2564,6 +2581,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
 	return ret ? : arch_populate_kprobe_blacklist();
 }
 
+#if IS_ENABLED(CONFIG_MODULES)
 static void add_module_kprobe_blacklist(struct module *mod)
 {
 	unsigned long start, end;
@@ -2665,6 +2683,7 @@ static struct notifier_block kprobe_module_nb = {
 	.notifier_call = kprobes_module_callback,
 	.priority = 0
 };
+#endif /* IS_ENABLED(CONFIG_MODULES) */
 
 void kprobe_free_init_mem(void)
 {
@@ -2724,8 +2743,11 @@ static int __init init_kprobes(void)
 	err = arch_init_kprobes();
 	if (!err)
 		err = register_die_notifier(&kprobe_exceptions_nb);
+
+#if IS_ENABLED(CONFIG_MODULES)
 	if (!err)
 		err = register_module_notifier(&kprobe_module_nb);
+#endif
 
 	kprobes_initialized = (err == 0);
 	kprobe_sysctls_init();
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index c4c6e0e0068b..dd4598f775b9 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -102,6 +102,7 @@ static nokprobe_inline bool trace_kprobe_has_gone(struct trace_kprobe *tk)
 	return kprobe_gone(&tk->rp.kp);
 }
 
+#if IS_ENABLED(CONFIG_MODULES)
 static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
 						 struct module *mod)
 {
@@ -129,6 +130,12 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
 
 	return ret;
 }
+#else
+static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
+{
+	return true;
+}
+#endif
 
 static bool trace_kprobe_is_busy(struct dyn_event *ev)
 {
@@ -670,6 +677,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
 	return ret;
 }
 
+#if IS_ENABLED(CONFIG_MODULES)
 /* Module notifier call back, checking event on the module */
 static int trace_kprobe_module_callback(struct notifier_block *nb,
 				       unsigned long val, void *data)
@@ -704,6 +712,7 @@ static struct notifier_block trace_kprobe_module_nb = {
 	.notifier_call = trace_kprobe_module_callback,
 	.priority = 1	/* Invoked after kprobe module callback */
 };
+#endif /* IS_ENABLED(CONFIG_MODULES) */
 
 static int count_symbols(void *data, unsigned long unused)
 {
@@ -1897,8 +1906,10 @@ static __init int init_kprobe_trace_early(void)
 	if (ret)
 		return ret;
 
+#if IS_ENABLED(CONFIG_MODULES)
 	if (register_module_notifier(&trace_kprobe_module_nb))
 		return -EINVAL;
+#endif
 
 	return 0;
 }
-- 
2.43.0