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

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

----- On Oct 12, 2018, at 4:05 PM, 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:

Actually, the above sentence should read:

"However, it does so without turning struct tracepoint * const into const int
elsewhere in the tracepoint code [...]" (I had mistakenly worded it "const int *").

Thanks,

Mathieu


> 
> 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.
> 
> 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>
> 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          |  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