kprobes, extable: Identify kprobes trampolines as kernel text area

Improve __kernel_text_address()/kernel_text_address() to return
true if the given address is on a kprobe's instruction slot
trampoline.

This can help stacktraces to determine the address is on a
text area or not.

To implement this atomically in is_kprobe_*_slot(), also change
the insn_cache page list to an RCU list.

This changes timings a bit (it delays page freeing to the RCU garbage
collection phase), but none of that is in the hot path.

Note: this change can add small overhead to stack unwinders because
it adds 2 additional checks to __kernel_text_address(). However, the
impact should be very small, because kprobe_insn_pages list has 1 entry
per 256 probes(on x86, on arm/arm64 it will be 1024 probes),
and kprobe_optinsn_pages has 1 entry per 32 probes(on x86).
In most use cases, the number of kprobe events may be less
than 20, which means that is_kprobe_*_slot() will check just one entry.

Tested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/148388747896.6869.6354262871751682264.stgit@devbox
[ Improved the changelog and coding style. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 29 insertions, 1 deletions

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 8f6849084248..16ddfb8b304a 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -278,9 +278,13 @@ struct kprobe_insn_cache {
 	int nr_garbage;
 };
 
+#ifdef __ARCH_WANT_KPROBES_INSN_SLOT
 extern kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c);
 extern void __free_insn_slot(struct kprobe_insn_cache *c,
 			     kprobe_opcode_t *slot, int dirty);
+/* sleep-less address checking routine  */
+extern bool __is_insn_slot_addr(struct kprobe_insn_cache *c,
+				unsigned long addr);
 
 #define DEFINE_INSN_CACHE_OPS(__name)					\
 extern struct kprobe_insn_cache kprobe_##__name##_slots;		\
@@ -294,6 +298,18 @@ static inline void free_##__name##_slot(kprobe_opcode_t *slot, int dirty)\
 {									\
 	__free_insn_slot(&kprobe_##__name##_slots, slot, dirty);	\
 }									\
+									\
+static inline bool is_kprobe_##__name##_slot(unsigned long addr)	\
+{									\
+	return __is_insn_slot_addr(&kprobe_##__name##_slots, addr);	\
+}
+#else /* __ARCH_WANT_KPROBES_INSN_SLOT */
+#define DEFINE_INSN_CACHE_OPS(__name)					\
+static inline bool is_kprobe_##__name##_slot(unsigned long addr)	\
+{									\
+	return 0;							\
+}
+#endif
 
 DEFINE_INSN_CACHE_OPS(insn);
 
@@ -330,7 +346,6 @@ extern int proc_kprobes_optimization_handler(struct ctl_table *table,
 					     int write, void __user *buffer,
 					     size_t *length, loff_t *ppos);
 #endif
-
 #endif /* CONFIG_OPTPROBES */
 #ifdef CONFIG_KPROBES_ON_FTRACE
 extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
@@ -481,6 +496,19 @@ static inline int enable_jprobe(struct jprobe *jp)
 	return enable_kprobe(&jp->kp);
 }
 
+#ifndef CONFIG_KPROBES
+static inline bool is_kprobe_insn_slot(unsigned long addr)
+{
+	return false;
+}
+#endif
+#ifndef CONFIG_OPTPROBES
+static inline bool is_kprobe_optinsn_slot(unsigned long addr)
+{
+	return false;
+}
+#endif
+
 #ifdef CONFIG_KPROBES
 /*
  * Blacklist ganerating macro. Specify functions which is not probed