[PATCH v7 1/2] kprobes: Implement trampoline memory allocator for tracing
Jarkko Sakkinen
jarkko at kernel.org
Tue Mar 26 06:46:15 PDT 2024
Tracing with kprobes while running a monolithic kernel is currently
impossible because CONFIG_KPROBES depends on CONFIG_MODULES.
Introduce alloc_execmem() and free_execmem() for allocating executable
memory. If an arch implements these functions, it can mark this up with
the HAVE_ALLOC_EXECMEM kconfig flag.
The second new kconfig flag is ALLOC_EXECMEM, which can be selected if
either MODULES is selected or HAVE_ALLOC_EXECMEM is support by the arch. If
HAVE_ALLOC_EXECMEM is not supported by an arch, module_alloc() and
module_memfree() are used as a fallback, thus retaining backwards
compatibility to earlier kernel versions.
This will allow architecture to enable kprobes traces without requiring
to enable module.
The support can be implemented with four easy steps:
1. Implement alloc_execmem().
2. Implement free_execmem().
3. Edit arch/<arch>/Makefile.
4. Set HAVE_ALLOC_EXECMEM in arch/<arch>/Kconfig.
Link: https://lore.kernel.org/all/20240325115632.04e37297491cadfbbf382767@kernel.org/
Suggested-by: Masami Hiramatsu <mhiramat at kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko at kernel.org>
---
v7:
- Use "depends on" for ALLOC_EXECMEM instead of "select"
- Reduced and narrowed CONFIG_MODULES checks further in kprobes.c.
v6:
- Use null pointer for notifiers and register the module notifier only if
IS_ENABLED(CONFIG_MODULES) is set.
- Fixed typo in the commit message and wrote more verbose description
of the feature.
v5:
- alloc_execmem() was missing GFP_KERNEL parameter. The patch set did
compile because 2/2 had the fixup (leaked there when rebasing the
patch set).
v4:
- Squashed a couple of unrequired CONFIG_MODULES checks.
- See https://lore.kernel.org/all/D034M18D63EC.2Y11D954YSZYK@kernel.org/
v3:
- A new patch added.
- For IS_DEFINED() I need advice as I could not really find that many
locations where it would be applicable.
---
arch/Kconfig | 17 +++++++++++-
include/linux/execmem.h | 13 +++++++++
kernel/kprobes.c | 53 ++++++++++++++++++++++---------------
kernel/trace/trace_kprobe.c | 15 +++++++++--
4 files changed, 73 insertions(+), 25 deletions(-)
create mode 100644 include/linux/execmem.h
diff --git a/arch/Kconfig b/arch/Kconfig
index a5af0edd3eb8..5e9735f60f3c 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
+ depends on ALLOC_EXECMEM
select KALLSYMS
select TASKS_RCU if PREEMPTION
help
@@ -215,6 +215,21 @@ config HAVE_OPTPROBES
config HAVE_KPROBES_ON_FTRACE
bool
+config HAVE_ALLOC_EXECMEM
+ bool
+ help
+ Architectures that select this option are capable of allocating trampoline
+ executable memory for tracing subsystems, indepedently of the kernel module
+ subsystem.
+
+config ALLOC_EXECMEM
+ bool "Executable (trampoline) memory allocation"
+ default y
+ depends on MODULES || HAVE_ALLOC_EXECMEM
+ help
+ Select this for executable (trampoline) memory. Can be enabled when either
+ module allocator or arch-specific allocator is available.
+
config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
bool
help
diff --git a/include/linux/execmem.h b/include/linux/execmem.h
new file mode 100644
index 000000000000..ae2ff151523a
--- /dev/null
+++ b/include/linux/execmem.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_EXECMEM_H
+#define _LINUX_EXECMEM_H
+
+#ifdef CONFIG_HAVE_ALLOC_EXECMEM
+void *alloc_execmem(unsigned long size, gfp_t gfp);
+void free_execmem(void *region);
+#else
+#define alloc_execmem(size, gfp) module_alloc(size)
+#define free_execmem(region) module_memfree(region)
+#endif
+
+#endif /* _LINUX_EXECMEM_H */
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 9d9095e81792..13bef5de315c 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -44,6 +44,7 @@
#include <asm/cacheflush.h>
#include <asm/errno.h>
#include <linux/uaccess.h>
+#include <linux/execmem.h>
#define KPROBE_HASH_BITS 6
#define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
@@ -113,17 +114,17 @@ enum kprobe_slot_state {
void __weak *alloc_insn_page(void)
{
/*
- * Use module_alloc() so this page is within +/- 2GB of where the
+ * Use alloc_execmem() so this page is within +/- 2GB of where the
* kernel image and loaded module images reside. This is required
* for most of the architectures.
* (e.g. x86-64 needs this to handle the %rip-relative fixups.)
*/
- return module_alloc(PAGE_SIZE);
+ return alloc_execmem(PAGE_SIZE, GFP_KERNEL);
}
static void free_insn_page(void *page)
{
- module_memfree(page);
+ free_execmem(page);
}
struct kprobe_insn_cache kprobe_insn_slots = {
@@ -1592,6 +1593,7 @@ 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.
@@ -1602,7 +1604,9 @@ static int check_kprobe_address_safe(struct kprobe *p,
*probed_mod = NULL;
ret = -ENOENT;
}
+#endif /* CONFIG_MODULES */
}
+
out:
preempt_enable();
jump_label_unlock();
@@ -2482,24 +2486,6 @@ 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)
{
@@ -2564,6 +2550,25 @@ 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;
@@ -2660,6 +2665,9 @@ 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,
@@ -2724,7 +2732,8 @@ 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 c4c6e0e0068b..13ea0d0994d5 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,
@@ -1897,8 +1905,11 @@ 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;
}
--
2.44.0
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