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Subject[PATCH for 4.19] tracepoint: Fix: tracepoint array element size mismatch
Date
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.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Link: http://lkml.kernel.org/r/20180704083651.24360-7-ard.biesheuvel@linaro.org
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morris <james.morris@microsoft.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/module.h | 3 ++-
include/linux/tracepoint-defs.h | 6 ++++++
include/linux/tracepoint.h | 36 +++++++++++++++++++++------------
kernel/tracepoint.c | 24 ++++++++--------------
4 files changed, 39 insertions(+), 30 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index f807f15bebbe..e19ae08c7fb8 100644
--- 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 22c5a46e9693..49ba9cde7e4b 100644
--- 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 041f7e56a289..538ba1a58f5b 100644
--- 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 bf2c06ef9afc..a3be42304485 100644
--- 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
--
2.17.1
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