[PATCH v2 4/4] kprobes: Remove core dependency on modules

Mark Rutland
2024-04-03T15:02:11Z

From: Jarkko Sakkinen <jarkko@kernel.org>

Tracing with kprobes while running a monolithic kernel is currently
impossible because KPROBES depends on MODULES. While this dependency is
necessary when HAVE_KPROBES_ALLOC=n and the core kprobes code allocates
memory using module_alloc(), 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=y when
HAVE_KPROBES_ALLOC=y.

As of this patch kprobes can be used when MODULES=n on arm64 and
riscv. All other architectures still depend on MODULES, either by virtue
of the core dependency on MODULES when HAVE_KPROBES_ALLOC=n, or by
virtue of an explciit dependency on MODULES in arch code.

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@kernel.org>
Link: https://lore.kernel.org/lkml/20240326134616.7691-1-jarkko@kernel.org/
[Mark: Remove execmem changes, depend on HAVE_KPROBES_ALLOC]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Will Deacon <will@kernel.org>
---
arch/Kconfig | 2 +-
kernel/kprobes.c | 46 ++++++++++++++++++++++---------------
kernel/trace/trace_kprobe.c | 15 ++++++++++--
3 files changed, 41 insertions(+), 22 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 85bb59f7b8c07..0df2c88547b3c 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -52,7 +52,7 @@ config GENERIC_ENTRY

config KPROBES
bool "Kprobes"
- depends on MODULES
+ depends on MODULES || HAVE_KPROBES_ALLOC
depends on HAVE_KPROBES
select KALLSYMS
select TASKS_RCU if PREEMPTION
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index fa2ee4e59eca2..ec4493a41b505 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1594,6 +1594,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
goto out;
}

+#ifdef CONFIG_MODULES
/*
* If the module freed '.init.text', we couldn't insert
* kprobes in there.
@@ -1604,7 +1605,9 @@ static int check_kprobe_address_safe(struct kprobe *p,
*probed_mod = NULL;
ret = -ENOENT;
}
+#endif /* CONFIG_MODULES */
}
+
out:
preempt_enable();
jump_label_unlock();
@@ -2484,24 +2487,6 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
return 0;
}

-/* Remove all symbols in given area from kprobe blacklist */
-static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
-{
- struct kprobe_blacklist_entry *ent, *n;
-
- list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
- if (ent->start_addr < start || ent->start_addr >= end)
- continue;
- list_del(&ent->list);
- kfree(ent);
- }
-}
-
-static void kprobe_remove_ksym_blacklist(unsigned long entry)
-{
- kprobe_remove_area_blacklist(entry, entry + 1);
-}
-
int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
char *type, char *sym)
{
@@ -2566,6 +2551,25 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
return ret ? : arch_populate_kprobe_blacklist();
}

+#ifdef CONFIG_MODULES
+/* Remove all symbols in given area from kprobe blacklist */
+static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
+{
+ struct kprobe_blacklist_entry *ent, *n;
+
+ list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
+ if (ent->start_addr < start || ent->start_addr >= end)
+ continue;
+ list_del(&ent->list);
+ kfree(ent);
+ }
+}
+
+static void kprobe_remove_ksym_blacklist(unsigned long entry)
+{
+ kprobe_remove_area_blacklist(entry, entry + 1);
+}
+
static void add_module_kprobe_blacklist(struct module *mod)
{
unsigned long start, end;
@@ -2662,6 +2666,9 @@ 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 +2733,8 @@ 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