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Subject[PATCH V4 03/13] kprobes: Add symbols for kprobe insn pages
Date
Symbols are needed for tools to describe instruction addresses. Pages
allocated for kprobe's purposes need symbols to be created for them.
Add such symbols to be visible via /proc/kallsyms.

Note: kprobe insn pages are not used if ftrace is configured. To see the
effect of this patch, the kernel must be configured with:

# CONFIG_FUNCTION_TRACER is not set
CONFIG_KPROBES=y

and for optimised kprobes:

CONFIG_OPTPROBES=y

Example on x86:

# perf probe __schedule
Added new event:
probe:__schedule (on __schedule)
# cat /proc/kallsyms | grep '\[__builtin__kprobes\]'
ffffffffc00d4000 t kprobe_insn_page [__builtin__kprobes]
ffffffffc00d6000 t kprobe_optinsn_page [__builtin__kprobes]

Note: This patch adds "__builtin__kprobes" as a module name in
/proc/kallsyms for symbols for pages allocated for kprobes' purposes, even
though "__builtin__kprobes" is not a module.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
include/linux/kprobes.h | 15 ++++++++++++++
kernel/kallsyms.c | 37 +++++++++++++++++++++++++++++----
kernel/kprobes.c | 45 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 93 insertions(+), 4 deletions(-)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 04bdaf01112c..62d682f47b5e 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -242,6 +242,7 @@ struct kprobe_insn_cache {
struct mutex mutex;
void *(*alloc)(void); /* allocate insn page */
void (*free)(void *); /* free insn page */
+ const char *sym; /* symbol for insn pages */
struct list_head pages; /* list of kprobe_insn_page */
size_t insn_size; /* size of instruction slot */
int nr_garbage;
@@ -272,6 +273,8 @@ static inline bool is_kprobe_##__name##_slot(unsigned long addr) \
{ \
return __is_insn_slot_addr(&kprobe_##__name##_slots, addr); \
}
+#define KPROBE_INSN_PAGE_SYM "kprobe_insn_page"
+#define KPROBE_OPTINSN_PAGE_SYM "kprobe_optinsn_page"
#else /* __ARCH_WANT_KPROBES_INSN_SLOT */
#define DEFINE_INSN_CACHE_OPS(__name) \
static inline bool is_kprobe_##__name##_slot(unsigned long addr) \
@@ -373,6 +376,13 @@ void dump_kprobe(struct kprobe *kp);
void *alloc_insn_page(void);
void free_insn_page(void *page);

+int kprobe_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+ char *sym);
+int kprobe_cache_get_kallsym(struct kprobe_insn_cache *c, unsigned int *symnum,
+ unsigned long *value, char *type, char *sym);
+
+int arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
+ char *type, char *sym);
#else /* !CONFIG_KPROBES: */

static inline int kprobes_built_in(void)
@@ -435,6 +445,11 @@ static inline bool within_kprobe_blacklist(unsigned long addr)
{
return true;
}
+static inline int kprobe_get_kallsym(unsigned int symnum, unsigned long *value,
+ char *type, char *sym)
+{
+ return -ERANGE;
+}
#endif /* CONFIG_KPROBES */
static inline int disable_kretprobe(struct kretprobe *rp)
{
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 136ce049c4ad..4a93511e6243 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -24,6 +24,7 @@
#include <linux/slab.h>
#include <linux/filter.h>
#include <linux/ftrace.h>
+#include <linux/kprobes.h>
#include <linux/compiler.h>

/*
@@ -438,6 +439,7 @@ struct kallsym_iter {
loff_t pos_arch_end;
loff_t pos_mod_end;
loff_t pos_ftrace_mod_end;
+ loff_t pos_bpf_end;
unsigned long value;
unsigned int nameoff; /* If iterating in core kernel symbols. */
char type;
@@ -497,11 +499,33 @@ static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)

static int get_ksymbol_bpf(struct kallsym_iter *iter)
{
+ int ret;
+
strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
iter->exported = 0;
- return bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
- &iter->value, &iter->type,
- iter->name) < 0 ? 0 : 1;
+ ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
+ &iter->value, &iter->type,
+ iter->name);
+ if (ret < 0) {
+ iter->pos_bpf_end = iter->pos;
+ return 0;
+ }
+
+ return 1;
+}
+
+/*
+ * This uses "__builtin__kprobes" as a module name for symbols for pages
+ * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
+ * module.
+ */
+static int get_ksymbol_kprobe(struct kallsym_iter *iter)
+{
+ strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
+ iter->exported = 0;
+ return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
+ &iter->value, &iter->type,
+ iter->name) < 0 ? 0 : 1;
}

/* Returns space to next name. */
@@ -528,6 +552,7 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
iter->pos_arch_end = 0;
iter->pos_mod_end = 0;
iter->pos_ftrace_mod_end = 0;
+ iter->pos_bpf_end = 0;
}
}

@@ -552,7 +577,11 @@ static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
get_ksymbol_ftrace_mod(iter))
return 1;

- return get_ksymbol_bpf(iter);
+ if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
+ get_ksymbol_bpf(iter))
+ return 1;
+
+ return get_ksymbol_kprobe(iter);
}

/* Returns false if pos at or past end of file. */
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 2625c241ac00..229d1b596690 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -118,6 +118,7 @@ struct kprobe_insn_cache kprobe_insn_slots = {
.mutex = __MUTEX_INITIALIZER(kprobe_insn_slots.mutex),
.alloc = alloc_insn_page,
.free = free_insn_page,
+ .sym = KPROBE_INSN_PAGE_SYM,
.pages = LIST_HEAD_INIT(kprobe_insn_slots.pages),
.insn_size = MAX_INSN_SIZE,
.nr_garbage = 0,
@@ -296,6 +297,7 @@ struct kprobe_insn_cache kprobe_optinsn_slots = {
.mutex = __MUTEX_INITIALIZER(kprobe_optinsn_slots.mutex),
.alloc = alloc_insn_page,
.free = free_insn_page,
+ .sym = KPROBE_OPTINSN_PAGE_SYM,
.pages = LIST_HEAD_INIT(kprobe_optinsn_slots.pages),
/* .insn_size is initialized later */
.nr_garbage = 0,
@@ -2179,6 +2181,49 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
return 0;
}

+int kprobe_cache_get_kallsym(struct kprobe_insn_cache *c, unsigned int *symnum,
+ unsigned long *value, char *type, char *sym)
+{
+ struct kprobe_insn_page *kip;
+ int ret = -ERANGE;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(kip, &c->pages, list) {
+ if ((*symnum)--)
+ continue;
+ strlcpy(sym, c->sym, KSYM_NAME_LEN);
+ *type = 't';
+ *value = (unsigned long)kip->insns;
+ ret = 0;
+ break;
+ }
+ rcu_read_unlock();
+
+ return ret;
+}
+
+int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
+ char *type, char *sym)
+{
+ return -ERANGE;
+}
+
+int kprobe_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+ char *sym)
+{
+#ifdef __ARCH_WANT_KPROBES_INSN_SLOT
+ if (!kprobe_cache_get_kallsym(&kprobe_insn_slots, &symnum, value, type, sym))
+ return 0;
+#ifdef CONFIG_OPTPROBES
+ if (!kprobe_cache_get_kallsym(&kprobe_optinsn_slots, &symnum, value, type, sym))
+ return 0;
+#endif
+#endif
+ if (!arch_kprobe_get_kallsym(&symnum, value, type, sym))
+ return 0;
+ return -ERANGE;
+}
+
int __init __weak arch_populate_kprobe_blacklist(void)
{
return 0;
--
2.17.1
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