[PATCH 4/4] kprobes: Remove core dependency on modules

[Mark Rutland]

From: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

Tracing with kprobes while running a monolithic kernel is currently
impossible because KPROBES depends on MODULES. While this dependency is
necessary when KPROBES_USE_MODULE_ALLOC=y, all the other module-specific
code only exist to handle the case when MODULES=y, and can be hidden
behind ifdeffery.

Add the necessary ifdeffery, and remove the dependency on MODULES=N when
KPROBES_USE_MODULE_ALLOC=n.

Currently this allows kprobes to be used when CONFIG_MODULES=n on arm64
and riscv, and other architectures can enable support by implementing
their own kprobes_alloc_insn_page() and kprobes_free_insn_page() which
do not depend on MODULES.

Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
Link: https://lore.kernel.org/all/20240326012102.27438-1-jarkko@xxxxxxxxxx/
[Mark: Remove execmem changes, depend on !KPROBES_USE_MODULE_ALLOC]
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxx>
---
 arch/Kconfig                |  2 +-
 kernel/kprobes.c            | 12 +++++++++++-
 kernel/trace/trace_kprobe.c | 15 +++++++++++++--
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 85bb59f7b8c07..cf43de9ffb5b9 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -52,7 +52,7 @@ config GENERIC_ENTRY
 
 config KPROBES
 	bool "Kprobes"
-	depends on MODULES
+	depends on MODULES || !KPROBES_USE_MODULE_ALLOC
 	depends on HAVE_KPROBES
 	select KALLSYMS
 	select TASKS_RCU if PREEMPTION
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index fa2ee4e59eca2..7c2f0b504cdcb 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1582,6 +1582,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
 		goto out;
 	}
 
+#ifdef CONFIG_MODULES
 	/* Check if 'p' is probing a module. */
 	*probed_mod = __module_text_address((unsigned long) p->addr);
 	if (*probed_mod) {
@@ -1605,6 +1606,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
 			ret = -ENOENT;
 		}
 	}
+#endif
+
 out:
 	preempt_enable();
 	jump_label_unlock();
@@ -2484,6 +2487,7 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
 	return 0;
 }
 
+#ifdef CONFIG_MODULES
 /* Remove all symbols in given area from kprobe blacklist */
 static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
 {
@@ -2501,6 +2505,7 @@ static void kprobe_remove_ksym_blacklist(unsigned long entry)
 {
 	kprobe_remove_area_blacklist(entry, entry + 1);
 }
+#endif /* CONFIG_MODULES */
 
 int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
 				   char *type, char *sym)
@@ -2566,6 +2571,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
 	return ret ? : arch_populate_kprobe_blacklist();
 }
 
+#ifdef CONFIG_MODULES
 static void add_module_kprobe_blacklist(struct module *mod)
 {
 	unsigned long start, end;
@@ -2662,6 +2668,9 @@ static int kprobes_module_callback(struct notifier_block *nb,
 	mutex_unlock(&kprobe_mutex);
 	return NOTIFY_DONE;
 }
+#else
+#define kprobes_module_callback	(NULL)
+#endif /* CONFIG_MODULES */
 
 static struct notifier_block kprobe_module_nb = {
 	.notifier_call = kprobes_module_callback,
@@ -2726,7 +2735,8 @@ static int __init init_kprobes(void)
 	err = arch_init_kprobes();
 	if (!err)
 		err = register_die_notifier(&kprobe_exceptions_nb);
-	if (!err)
+
+	if (!err && IS_ENABLED(CONFIG_MODULES))
 		err = register_module_notifier(&kprobe_module_nb);
 
 	kprobes_initialized = (err == 0);
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 14099cc17fc9e..c509ba776e679 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -111,6 +111,7 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
 	return strncmp(module_name(mod), name, len) == 0 && name[len] == ':';
 }
 
+#ifdef CONFIG_MODULES
 static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
 {
 	char *p;
@@ -129,6 +130,9 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
 
 	return ret;
 }
+#else
+#define trace_kprobe_module_exist(tk) false /* aka a module never exists */
+#endif /* CONFIG_MODULES */
 
 static bool trace_kprobe_is_busy(struct dyn_event *ev)
 {
@@ -670,6 +674,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
 	return ret;
 }
 
+#ifdef 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)
@@ -699,6 +704,9 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
 
 	return NOTIFY_DONE;
 }
+#else
+#define trace_kprobe_module_callback (NULL)
+#endif /* CONFIG_MODULES */
 
 static struct notifier_block trace_kprobe_module_nb = {
 	.notifier_call = trace_kprobe_module_callback,
@@ -1933,8 +1941,11 @@ static __init int init_kprobe_trace_early(void)
 	if (ret)
 		return ret;
 
-	if (register_module_notifier(&trace_kprobe_module_nb))
-		return -EINVAL;
+	if (IS_ENABLED(CONFIG_MODULES)) {
+		ret = register_module_notifier(&trace_kprobe_module_nb);
+		if (ret)
+			return -EINVAL;
+	}
 
 	return 0;
 }
-- 
2.30.2