Re: [PATCH for 4.19] tracepoint: Fix: out-of-bound tracepoint array iteration

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On Oct 13, 2018, at 11:24 AM, Ard Biesheuvel ard.biesheuvel@linaro.org wrote:

> On 12 October 2018 at 23:07, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>> Hi Mathieu,
>>
>> On 12 October 2018 at 22:05, Mathieu Desnoyers
>> <mathieu.desnoyers@efficios.com> wrote:
>>> 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:
>>>
>>> tracepoint_module_{coming,going} invoke
>>> tp_module_going_check_quiescent() with mod->tracepoints_ptrs
>>> as first argument, and computes the end address of the array
>>> for the second argument with:
>>>
>>>   mod->tracepoints_ptrs + mod->num_tracepoints
>>>
>>> However, because the type of mod->tracepoint_ptrs in module.h
>>> has not been changed from pointer to int, it passes an end
>>> pointer which is twice larger than the array, causing out-of-bound
>>> array accesses.
>>>
>>> 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.
>>>
>>
>> Apologies for the breakage. FWIW, this looks like the correct approach
>> to me (and mirrors what I did for initcalls in the same series)
>>
>>> This issue appears in 4.19-rc kernels, and should ideally be fixed
>>> before the end of the rc cycle.
>>>
>>
>> +1
>>
>>> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>>> 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>
>>
>> Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>>
> 
> This fixes the build breakage for me that kbuild test robot reports.
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index cdab2451d6be..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>

You've beat me to it :) I'll fold this change in a v2 of the patch,

Thanks!

Mathieu

> 
> #include <linux/percpu.h>
> #include <asm/module.h>
> 
> 
> 
> 
> 
>>> ---
>>>  include/linux/module.h          |  2 +-
>>>  include/linux/tracepoint-defs.h |  6 ++++++
>>>  include/linux/tracepoint.h      | 36 +++++++++++++++++++++------------
>>>  kernel/tracepoint.c             | 24 ++++++++--------------
>>>  4 files changed, 38 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/include/linux/module.h b/include/linux/module.h
>>> index f807f15bebbe..cdab2451d6be 100644
>>> --- a/include/linux/module.h
>>> +++ b/include/linux/module.h
>>> @@ -430,7 +430,7 @@ 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

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com