kprobes: unify insn caches

The current kpropes insn caches allocate memory areas for insn slots
with module_alloc().  The assumption is that the kernel image and module
area are both within the same +/- 2GB memory area.

This however is not true for s390 where the kernel image resides within
the first 2GB (DMA memory area), but the module area is far away in the
vmalloc area, usually somewhere close below the 4TB area.

For new pc relative instructions s390 needs insn slots that are within
+/- 2GB of each area.  That way we can patch displacements of
pc-relative instructions within the insn slots just like x86 and
powerpc.

The module area works already with the normal insn slot allocator,
however there is currently no way to get insn slots that are within the
first 2GB on s390 (aka DMA area).

Therefore this patch set modifies the kprobes insn slot cache code in
order to allow to specify a custom allocator for the insn slot cache
pages.  In addition architecure can now have private insn slot caches
withhout the need to modify common code.

Patch 1 unifies and simplifies the current insn and optinsn caches
        implementation. This is a preparation which allows to add more
        insn caches in a simple way.

Patch 2 adds the possibility to specify a custom allocator.

Patch 3 makes s390 use the new insn slot mechanisms and adds support for
        pc-relative instructions with long displacements.

This patch (of 3):

The two insn caches (insn, and optinsn) each have an own mutex and
alloc/free functions (get_[opt]insn_slot() / free_[opt]insn_slot()).

Since there is the need for yet another insn cache which satifies dma
allocations on s390, unify and simplify the current implementation:

- Move the per insn cache mutex into struct kprobe_insn_cache.
- Move the alloc/free functions to kprobe.h so they are simply
  wrappers for the generic __get_insn_slot/__free_insn_slot functions.
  The implementation is done with a DEFINE_INSN_CACHE_OPS() macro
  which provides the alloc/free functions for each cache if needed.
- move the struct kprobe_insn_cache to kprobe.h which allows to generate
  architecture specific insn slot caches outside of the core kprobes
  code.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 28 insertions, 4 deletions

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index ca1d27a0d6a6..077f65321b5e 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -264,10 +264,34 @@ extern void arch_arm_kprobe(struct kprobe *p);
 extern void arch_disarm_kprobe(struct kprobe *p);
 extern int arch_init_kprobes(void);
 extern void show_registers(struct pt_regs *regs);
-extern kprobe_opcode_t *get_insn_slot(void);
-extern void free_insn_slot(kprobe_opcode_t *slot, int dirty);
 extern void kprobes_inc_nmissed_count(struct kprobe *p);
 
+struct kprobe_insn_cache {
+        struct mutex mutex;
+        struct list_head pages; /* list of kprobe_insn_page */
+        size_t insn_size;       /* size of instruction slot */
+        int nr_garbage;
+};
+
+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);
+
+#define DEFINE_INSN_CACHE_OPS(__name)                                   \
+extern struct kprobe_insn_cache kprobe_##__name##_slots;                \
+                                                                        \
+static inline kprobe_opcode_t *get_##__name##_slot(void)                \
+{                                                                       \
+        return __get_insn_slot(&kprobe_##__name##_slots);               \
+}                                                                       \
+                                                                        \
+static inline void free_##__name##_slot(kprobe_opcode_t *slot, int dirty)\
+{                                                                       \
+        __free_insn_slot(&kprobe_##__name##_slots, slot, dirty);        \
+}                                                                       \
+
+DEFINE_INSN_CACHE_OPS(insn);
+
 #ifdef CONFIG_OPTPROBES
 /*
  * Internal structure for direct jump optimized probe
@@ -287,13 +311,13 @@ extern void arch_optimize_kprobes(struct list_head *oplist);
 extern void arch_unoptimize_kprobes(struct list_head *oplist,
                                     struct list_head *done_list);
 extern void arch_unoptimize_kprobe(struct optimized_kprobe *op);
-extern kprobe_opcode_t *get_optinsn_slot(void);
-extern void free_optinsn_slot(kprobe_opcode_t *slot, int dirty);
 extern int arch_within_optimized_kprobe(struct optimized_kprobe *op,
                                         unsigned long addr);
 
 extern void opt_pre_handler(struct kprobe *p, struct pt_regs *regs);
 
+DEFINE_INSN_CACHE_OPS(optinsn);
+
 #ifdef CONFIG_SYSCTL
 extern int sysctl_kprobes_optimization;
 extern int proc_kprobes_optimization_handler(struct ctl_table *table,