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

Ard Biesheuvel
2018-10-13T15:24:23Z

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>

#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
>>