tracepoint: Fix tracepoint array element size mismatch

commit 46e0c9be206f ("kernel: tracepoints: add support for relative
references") changes the layout of the __tracepoint_ptrs section on
architectures supporting relative references. However, it does so
without turning struct tracepoint * const into const int elsewhere in
the tracepoint code, which has the following side-effect:

Setting mod->num_tracepoints is done in by module.c:

    mod->tracepoints_ptrs = section_objs(info, "__tracepoints_ptrs",
                                         sizeof(*mod->tracepoints_ptrs),
                                         &mod->num_tracepoints);

Basically, since sizeof(*mod->tracepoints_ptrs) is a pointer size
(rather than sizeof(int)), num_tracepoints is erroneously set to half the
size it should be on 64-bit arch. So a module with an odd number of
tracepoints misses the last tracepoint due to effect of integer
division.

So in the module going notifier:

        for_each_tracepoint_range(mod->tracepoints_ptrs,
                mod->tracepoints_ptrs + mod->num_tracepoints,
                tp_module_going_check_quiescent, NULL);

the expression (mod->tracepoints_ptrs + mod->num_tracepoints) actually
evaluates to something within the bounds of the array, but miss the
last tracepoint if the number of tracepoints is odd on 64-bit arch.

Fix this by introducing a new typedef: tracepoint_ptr_t, which
is either "const int" on architectures that have PREL32 relocations,
or "struct tracepoint * const" on architectures that does not have
this feature.

Also provide a new tracepoint_ptr_defer() static inline to
encapsulate deferencing this type rather than duplicate code and
ugly idefs within the for_each_tracepoint_range() implementation.

This issue appears in 4.19-rc kernels, and should ideally be fixed
before the end of the rc cycle.

Acked-by: Ard Biesheuvel <[email protected]>
Acked-by: Jessica Yu <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Cc: Michael Ellerman <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: James Morris <[email protected]>
Cc: James Morris <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Nicolas Pitre <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Russell King <[email protected]>
Cc: "Serge E. Hallyn" <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Mathieu Desnoyers <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

diff --git a/include/linux/module.h b/include/linux/module.h
index f807f15bebbe732b466d45d8d603991b4a1aa3ef..e19ae08c7fb84fb8c0172639324f5f80cfeb6ea5 100644 (file)
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -20,6 +20,7 @@
 #include <linux/export.h>
 #include <linux/rbtree_latch.h>
 #include <linux/error-injection.h>
+#include <linux/tracepoint-defs.h>
 
 #include <linux/percpu.h>
 #include <asm/module.h>
@@ -430,7 +431,7 @@ struct module {
 
 #ifdef CONFIG_TRACEPOINTS
        unsigned int num_tracepoints;
-       struct tracepoint * const *tracepoints_ptrs;
+       tracepoint_ptr_t *tracepoints_ptrs;
 #endif
 #ifdef HAVE_JUMP_LABEL
        struct jump_entry *jump_entries;

diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
index 22c5a46e969394bfeae34e834c69f497d370dce0..49ba9cde7e4bb5e1b6b66f4f94912a65df971906 100644 (file)
--- a/include/linux/tracepoint-defs.h
+++ b/include/linux/tracepoint-defs.h
@@ -35,6 +35,12 @@ struct tracepoint {
        struct tracepoint_func __rcu *funcs;
 };
 
+#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
+typedef const int tracepoint_ptr_t;
+#else
+typedef struct tracepoint * const tracepoint_ptr_t;
+#endif
+
 struct bpf_raw_event_map {
        struct tracepoint       *tp;
        void                    *bpf_func;

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 041f7e56a2894f3f800fc470d8a5bccaffc58b88..538ba1a58f5b25c13a51d96da996a058e9511dde 100644 (file)
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -99,6 +99,29 @@ extern void syscall_unregfunc(void);
 #define TRACE_DEFINE_ENUM(x)
 #define TRACE_DEFINE_SIZEOF(x)
 
+#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
+static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
+{
+       return offset_to_ptr(p);
+}
+
+#define __TRACEPOINT_ENTRY(name)                                       \
+       asm("   .section \"__tracepoints_ptrs\", \"a\"          \n"     \
+           "   .balign 4                                       \n"     \
+           "   .long   __tracepoint_" #name " - .              \n"     \
+           "   .previous                                       \n")
+#else
+static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
+{
+       return *p;
+}
+
+#define __TRACEPOINT_ENTRY(name)                                        \
+       static tracepoint_ptr_t __tracepoint_ptr_##name __used           \
+       __attribute__((section("__tracepoints_ptrs"))) =                 \
+               &__tracepoint_##name
+#endif
+
 #endif /* _LINUX_TRACEPOINT_H */
 
 /*
@@ -253,19 +276,6 @@ extern void syscall_unregfunc(void);
                return static_key_false(&__tracepoint_##name.key);      \
        }
 
-#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
-#define __TRACEPOINT_ENTRY(name)                                       \
-       asm("   .section \"__tracepoints_ptrs\", \"a\"          \n"     \
-           "   .balign 4                                       \n"     \
-           "   .long   __tracepoint_" #name " - .              \n"     \
-           "   .previous                                       \n")
-#else
-#define __TRACEPOINT_ENTRY(name)                                        \
-       static struct tracepoint * const __tracepoint_ptr_##name __used  \
-       __attribute__((section("__tracepoints_ptrs"))) =                 \
-               &__tracepoint_##name
-#endif
-
 /*
  * We have no guarantee that gcc and the linker won't up-align the tracepoint
  * structures, so we create an array of pointers that will be used for iteration

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index bf2c06ef9afc3d5c2a5eecb620aa9acb07a7bba5..a3be42304485fdc2b1643ee2e649351ba32641bf 100644 (file)
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -28,8 +28,8 @@
 #include <linux/sched/task.h>
 #include <linux/static_key.h>
 
-extern struct tracepoint * const __start___tracepoints_ptrs[];
-extern struct tracepoint * const __stop___tracepoints_ptrs[];
+extern tracepoint_ptr_t __start___tracepoints_ptrs[];
+extern tracepoint_ptr_t __stop___tracepoints_ptrs[];
 
 DEFINE_SRCU(tracepoint_srcu);
 EXPORT_SYMBOL_GPL(tracepoint_srcu);
@@ -371,25 +371,17 @@ int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
 }
 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
 
-static void for_each_tracepoint_range(struct tracepoint * const *begin,
-               struct tracepoint * const *end,
+static void for_each_tracepoint_range(
+               tracepoint_ptr_t *begin, tracepoint_ptr_t *end,
                void (*fct)(struct tracepoint *tp, void *priv),
                void *priv)
 {
+       tracepoint_ptr_t *iter;
+
        if (!begin)
                return;
-
-       if (IS_ENABLED(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)) {
-               const int *iter;
-
-               for (iter = (const int *)begin; iter < (const int *)end; iter++)
-                       fct(offset_to_ptr(iter), priv);
-       } else {
-               struct tracepoint * const *iter;
-
-               for (iter = begin; iter < end; iter++)
-                       fct(*iter, priv);
-       }
+       for (iter = begin; iter < end; iter++)
+               fct(tracepoint_ptr_deref(iter), priv);
 }
 
 #ifdef CONFIG_MODULES