On Fri, 04 Aug 2006 10:17:32 -0500 David Smith wrote:
> When inserting a kprobes probe into a loadable module, there isn't a way
> for the kprobes module to get a module reference (in order to find the
> base address of the module among perhaps other things).
>
> A kprobes probe needs the base address of the module in order to
> "relocate" the addresses of probe points (since the load address of the
> module can change from run to run of the kprobe).
>
> I've added a new function, module_get_byname(), that looks up a module
> by name and returns the module reference. Note that module_get_byname()
> also increments the module reference count. It does this so that the
> module won't be unloaded between the time that module_get_byname() is
> called and register_kprobe() is called.
>
> Here's an example of how it would be used from a kprobe:
>
> ====
> static struct module *mod = NULL;
>
> int init_module(void)
> {
> /* grab the module, making sure it won't get unloaded until
> * we're done */
> const char *mod_name = "joydev";
> if (module_get_byname(mod_name, &mod) != 0)
> return 1;
>
> /* Specify the address/offset where you want to insert
> * probe. If this were a real kprobe module, we'd "relocate"
> * our probe address based on the load address of the module
> * we're interested in. */
> kp.addr = (kprobe_opcode_t *) mod->module_core + 0;
>
> /* All set to register with Kprobes */
> register_kprobe(&kp);
> return 0;
> }
>
> void cleanup_module(void)
> {
> if (kp.addr != NULL)
> unregister_kprobe(&kp);
>
> /* allow the module to get unloaded, if needed */
> if (mod != NULL)
> module_put(mod);
> }
> ====
>
> I've included a patch that implements the new function.
>
> Signed-off-by: David Smith <[email protected]>
> ---
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 0dfb794..7464e29 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -374,6 +374,8 @@ extern void __module_put_and_exit(struct
> __attribute__((noreturn));
> #define module_put_and_exit(code) __module_put_and_exit(THIS_MODULE,
> code);
>
> +long module_get_byname(const char *mod_name, struct module **mod);
Why long instead of int?
> +
> #ifdef CONFIG_MODULE_UNLOAD
> unsigned int module_refcount(struct module *mod);
> void __symbol_put(const char *symbol);
> @@ -549,6 +551,11 @@ static inline int is_exported(const char
> return 0;
> }
>
> +static inline long module_get_byname(const char *mod_name, struct
> module **mod)
> +{
> + return 1;
> +}
> +
> static inline int register_module_notifier(struct notifier_block * nb)
> {
> /* no events will happen anyway, so this can always succeed */
> diff --git a/kernel/module.c b/kernel/module.c
> index 2a19cd4..30449ce 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -291,7 +291,27 @@ static struct module *find_module(const
> }
> return NULL;
> }
> +
> +long module_get_byname(const char *mod_name, struct module **mod)
> +{
> + *mod = NULL;
>
> + /* We must hold module_mutex before calling find_module(). */
> + if (mutex_lock_interruptible(&module_mutex) != 0)
> + return -EINTR;
> +
> + *mod = find_module(mod_name);
> + mutex_unlock(&module_mutex);
> + if (*mod) {
> + if (! strong_try_module_get(*mod)) {
no space following the '!'.
> + *mod = NULL;
> + return -EINVAL;
> + }
> + }
> + return 0;
> +}
> +EXPORT_SYMBOL(module_get_byname);
> +
> #ifdef CONFIG_SMP
> /* Number of blocks used and allocated. */
> static unsigned int pcpu_num_used, pcpu_num_allocated;
---
~Randy
-
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