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Message-ID: <20181015122323.pb3fuyfdjemin5y2@linux-8ccs>
Date: Mon, 15 Oct 2018 14:23:23 +0200
From: Jessica Yu <jeyu@...nel.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
Michael Ellerman <mpe@...erman.id.au>,
Ingo Molnar <mingo@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Arnd Bergmann <arnd@...db.de>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Catalin Marinas <catalin.marinas@....com>,
James Morris <james.morris@...rosoft.com>,
James Morris <jmorris@...ei.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Kees Cook <keescook@...omium.org>,
Nicolas Pitre <nico@...aro.org>,
Paul Mackerras <paulus@...ba.org>,
Petr Mladek <pmladek@...e.com>,
Russell King <linux@...linux.org.uk>,
"Serge E. Hallyn" <serge@...lyn.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Thomas Garnier <thgarnie@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Will Deacon <will.deacon@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH for 4.19] tracepoint: Fix: tracepoint array element size
mismatch
+++ 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@...icios.com>
>Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>Link: http://lkml.kernel.org/r/20180704083651.24360-7-ard.biesheuvel@linaro.org
>Cc: Michael Ellerman <mpe@...erman.id.au>
>Cc: Ingo Molnar <mingo@...nel.org>
>Cc: Steven Rostedt (VMware) <rostedt@...dmis.org>
>Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>Cc: Arnd Bergmann <arnd@...db.de>
>Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>Cc: Bjorn Helgaas <bhelgaas@...gle.com>
>Cc: Catalin Marinas <catalin.marinas@....com>
>Cc: James Morris <james.morris@...rosoft.com>
>Cc: James Morris <jmorris@...ei.org>
>Cc: Jessica Yu <jeyu@...nel.org>
>Cc: Josh Poimboeuf <jpoimboe@...hat.com>
>Cc: Kees Cook <keescook@...omium.org>
>Cc: Nicolas Pitre <nico@...aro.org>
>Cc: Paul Mackerras <paulus@...ba.org>
>Cc: Petr Mladek <pmladek@...e.com>
>Cc: Russell King <linux@...linux.org.uk>
>Cc: "Serge E. Hallyn" <serge@...lyn.com>
>Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
>Cc: Thomas Garnier <thgarnie@...gle.com>
>Cc: Thomas Gleixner <tglx@...utronix.de>
>Cc: Will Deacon <will.deacon@....com>
>Cc: Andrew Morton <akpm@...ux-foundation.org>
>Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Whoops, acked the first version of the patch instead of this one.
In any case, for module parts:
Acked-by: Jessica Yu <jeyu@...nel.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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