Re: [PATCH for 4.19] tracepoint: Fix: tracepoint array element size mismatch

[Jessica Yu <jeyu@kernel.org>]

+++ Mathieu Desnoyers [13/10/18 15:10 -0400]:
>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>

Whoops, acked the first version of the patch instead of this one.
In any case, for module parts:

Acked-by: Jessica Yu <jeyu@kernel.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
>