[PATCH RFC] kprobes: Remove MODULES dependency

Jarkko Sakkinen
2020-07-09T23:45:47Z

Remove MODULES dependency and migrate from module_alloc to vmalloc().
According to Andi, the history with this dependency is that kprobes
originally required custom LKM's, which does not hold today anymore.

Right now one has to compile LKM support only to enable kprobes. With
this change applied, it is somewhat easier to create custom test
kernel's with a proper debugging capabilities, thus making Linux more
developer friendly.

Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
---
arch/Kconfig | 1 -
arch/x86/kernel/kprobes/core.c | 5 +++--
kernel/kprobes.c | 22 ++++++++++++++++++++--
kernel/trace/trace_kprobe.c | 12 ++++++++++++
4 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 8cc35dc556c7..bb59cdf335ab 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -61,7 +61,6 @@ config OPROFILE_NMI_TIMER

config KPROBES
bool "Kprobes"
- depends on MODULES
depends on HAVE_KPROBES
select KALLSYMS
help
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index ada39ddbc922..dc7b8d6fd20d 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -42,6 +42,7 @@
#include <linux/moduleloader.h>
#include <linux/vmalloc.h>
#include <linux/pgtable.h>
+#include <linux/vmalloc.h>

#include <asm/text-patching.h>
#include <asm/cacheflush.h>
@@ -423,7 +424,7 @@ void *alloc_insn_page(void)
{
void *page;

- page = module_alloc(PAGE_SIZE);
+ page = vmalloc(PAGE_SIZE);
if (!page)
return NULL;

@@ -446,7 +447,7 @@ void *alloc_insn_page(void)
/* Recover page to RW mode before releasing it */
void free_insn_page(void *page)
{
- module_memfree(page);
+ vfree(page);
}

static int arch_copy_kprobe(struct kprobe *p)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 4a904cc56d68..02680642ea11 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -35,6 +35,7 @@
#include <linux/ftrace.h>
#include <linux/cpu.h>
#include <linux/jump_label.h>
+#include <linux/vmalloc.h>

#include <asm/sections.h>
#include <asm/cacheflush.h>
@@ -111,12 +112,12 @@ enum kprobe_slot_state {

void __weak *alloc_insn_page(void)
{
- return module_alloc(PAGE_SIZE);
+ return vmalloc(PAGE_SIZE);
}

void __weak free_insn_page(void *page)
{
- module_memfree(page);
+ vfree(page);
}

struct kprobe_insn_cache kprobe_insn_slots = {
@@ -563,8 +564,11 @@ static void kprobe_optimizer(struct work_struct *work)
mutex_lock(&kprobe_mutex);
cpus_read_lock();
mutex_lock(&text_mutex);
+
+#ifdef CONFIG_MODULES
/* Lock modules while optimizing kprobes */
mutex_lock(&module_mutex);
+#endif

/*
* Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
@@ -589,7 +593,9 @@ static void kprobe_optimizer(struct work_struct *work)
/* Step 4: Free cleaned kprobes after quiesence period */
do_free_cleaned_kprobes();

+#ifdef CONFIG_MODULES
mutex_unlock(&module_mutex);
+#endif
mutex_unlock(&text_mutex);
cpus_read_unlock();

@@ -739,6 +745,7 @@ static int reuse_unused_kprobe(struct kprobe *ap)
return 0;
}

+#ifdef CONFIG_MODULE
/* Remove optimized instructions */
static void kill_optimized_kprobe(struct kprobe *p)
{
@@ -764,6 +771,7 @@ static void kill_optimized_kprobe(struct kprobe *p)
/* Don't touch the code, because it is already freed. */
arch_remove_optimized_kprobe(op);
}
+#endif

static inline
void __prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
@@ -1608,6 +1616,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
goto out;
}

+#ifdef CONFIG_MODULE
/*
* If the module freed .init.text, we couldn't insert
* kprobes in there.
@@ -1618,6 +1627,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
*probed_mod = NULL;
ret = -ENOENT;
}
+#endif
}
out:
preempt_enable();
@@ -2090,6 +2100,7 @@ NOKPROBE_SYMBOL(pre_handler_kretprobe);

#endif /* CONFIG_KRETPROBES */

+#ifdef CONFIG_MODULE
/* Set the kprobe gone and remove its instruction buffer. */
static void kill_kprobe(struct kprobe *p)
{
@@ -2114,6 +2125,7 @@ static void kill_kprobe(struct kprobe *p)
*/
arch_remove_kprobe(p);
}
+#endif

/* Disable one kprobe */
int disable_kprobe(struct kprobe *kp)
@@ -2214,6 +2226,7 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
return 0;
}

+#ifdef CONFIG_MODULE
/* Remove all symbols in given area from kprobe blacklist */
static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
{
@@ -2231,6 +2244,7 @@ static void kprobe_remove_ksym_blacklist(unsigned long entry)
{
kprobe_remove_area_blacklist(entry, entry + 1);
}
+#endif

int __init __weak arch_populate_kprobe_blacklist(void)
{
@@ -2274,6 +2288,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
return ret ? : arch_populate_kprobe_blacklist();
}

+#ifdef CONFIG_MODULE
static void add_module_kprobe_blacklist(struct module *mod)
{
unsigned long start, end;
@@ -2375,6 +2390,7 @@ static struct notifier_block kprobe_module_nb = {
.notifier_call = kprobes_module_callback,
.priority = 0
};
+#endif /* CONFIG_MODULE */

/* Markers of _kprobe_blacklist section */
extern unsigned long __start_kprobe_blacklist[];
@@ -2425,8 +2441,10 @@ static int __init init_kprobes(void)
err = arch_init_kprobes();
if (!err)
err = register_die_notifier(&kprobe_exceptions_nb);
+#ifdef CONFIG_MODULE
if (!err)
err = register_module_notifier(&kprobe_module_nb);
+#endif

kprobes_initialized = (err == 0);

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index aefb6065b508..30969b38fce8 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -103,6 +103,7 @@ static nokprobe_inline bool trace_kprobe_has_gone(struct trace_kprobe *tk)
return !!(kprobe_gone(&tk->rp.kp));
}

+#ifdef CONFIG_MODULE
static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
struct module *mod)
{
@@ -110,7 +111,9 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
const char *name = trace_kprobe_symbol(tk);
return strncmp(mod->name, name, len) == 0 && name[len] == ':';
}
+#endif

+#ifdef CONFIG_MODULE
static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
{
char *p;
@@ -129,6 +132,7 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)

return ret;
}
+#endif

static bool trace_kprobe_is_busy(struct dyn_event *ev)
{
@@ -608,10 +612,12 @@ static int append_trace_kprobe(struct trace_kprobe *tk, struct trace_kprobe *to)

/* Register k*probe */
ret = __register_trace_kprobe(tk);
+#ifdef CONFIG_MODULE
if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
ret = 0;
}
+#endif

if (ret)
trace_probe_unlink(&tk->tp);
@@ -651,10 +657,12 @@ static int register_trace_kprobe(struct trace_kprobe *tk)

/* Register k*probe */
ret = __register_trace_kprobe(tk);
+#ifdef CONFIG_MODULE
if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
ret = 0;
}
+#endif

if (ret < 0)
unregister_kprobe_event(tk);
@@ -666,6 +674,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
return ret;
}

+#ifdef CONFIG_MODULE
/* Module notifier call back, checking event on the module */
static int trace_kprobe_module_callback(struct notifier_block *nb,
unsigned long val, void *data)
@@ -700,6 +709,7 @@ static struct notifier_block trace_kprobe_module_nb = {
.notifier_call = trace_kprobe_module_callback,
.priority = 1 /* Invoked after kprobe module callback */
};
+#endif

/* Convert certain expected symbols into '_' when generating event names */
static inline void sanitize_event_name(char *name)
@@ -1891,8 +1901,10 @@ static __init int init_kprobe_trace_early(void)
if (ret)
return ret;

+#ifdef CONFIG_MODULE
if (register_module_notifier(&trace_kprobe_module_nb))
return -EINVAL;
+#endif

return 0;
}
--
2.25.1