Re: [PATCH v3 1/2] module: verify address is read-only

[Kees Cook]

On Wed, Mar 22, 2017 at 7:55 PM, Eddie Kovsky <ewk@xxxxxxxxxxxx> wrote:
> Implement a mechanism to check if a module's address is in
> the rodata or ro_after_init sections. It mimics the exsiting functions
> that test if an address is inside a module's text section.
>
> Functions that take a module as an argument will be able to
> verify that the module is in a read-only section.
>
> Signed-off-by: Eddie Kovsky <ewk@xxxxxxxxxxxx>

Awesome! I'll be glad to have these.

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

Jessica, if this looks good to you, should this go via modules or via
my tree? If mine, can I have your Ack?

Thanks!

-Kees

> ---
> Changes in v3:
>  - Change function name is_module_ro_address() to
> is_module_rodata_address().
>  - Improve comments on is_module_rodata_address().
>  - Add a !CONFIG_MODULES stub for is_module_rodata_address.
>  - Correct and simplify the check for the read-only memory regions in
> the module address.
>
>  include/linux/module.h | 12 ++++++++++++
>  kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 65 insertions(+)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 9ad68561d8c2..66b7fd321334 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -492,7 +492,9 @@ static inline int module_is_live(struct module *mod)
>
>  struct module *__module_text_address(unsigned long addr);
>  struct module *__module_address(unsigned long addr);
> +struct module *__module_ro_address(unsigned long addr);
>  bool is_module_address(unsigned long addr);
> +bool is_module_rodata_address(unsigned long addr);
>  bool __is_module_percpu_address(unsigned long addr, unsigned long *can_addr);
>  bool is_module_percpu_address(unsigned long addr);
>  bool is_module_text_address(unsigned long addr);
> @@ -646,6 +648,16 @@ static inline struct module *__module_address(unsigned long addr)
>         return NULL;
>  }
>
> +static inline struct module *__module_ro_address(unsigned long addr)
> +{
> +       return NULL;
> +}
> +
> +static inline bool is_module_rodata_address(unsigned long addr)
> +{
> +       return false;
> +}
> +
>  static inline struct module *__module_text_address(unsigned long addr)
>  {
>         return NULL;
> diff --git a/kernel/module.c b/kernel/module.c
> index 8ffcd29a4245..99ada1257aaa 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -4292,6 +4292,59 @@ struct module *__module_text_address(unsigned long addr)
>  }
>  EXPORT_SYMBOL_GPL(__module_text_address);
>
> +/**
> + * is_module_rodata_address - is this address inside read-only module code?
> + * @addr: the address to check.
> + *
> + */
> +bool is_module_rodata_address(unsigned long addr)
> +{
> +       bool ret;
> +
> +       preempt_disable();
> +       ret = __module_ro_address(addr) != NULL;
> +       preempt_enable();
> +
> +       return ret;
> +}
> +
> +/*
> + * __module_ro_address - get the module whose rodata/ro_after_init sections
> + * contain the given address.
> + * @addr: the address.
> + *
> + * Must be called with preempt disabled or module mutex held so that
> + * module doesn't get freed during this.
> + */
> +struct module *__module_ro_address(unsigned long addr)
> +{
> +       struct module *mod = __module_address(addr);
> +
> +       void *init_base = mod->init_layout.base;
> +       unsigned int init_text_size = mod->init_layout.text_size;
> +       unsigned int init_ro_after_init_size = mod->init_layout.ro_after_init_size;
> +
> +       void *core_base = mod->core_layout.base;
> +       unsigned int core_text_size = mod->core_layout.text_size;
> +       unsigned int core_ro_after_init_size = mod->core_layout.ro_after_init_size;
> +
> +       /*
> +        * Make sure module is within the read-only section.
> +        * range(base + text_size, base + ro_after_init_size)
> +        * encompasses both the rodata and ro_after_init regions.
> +        * See comment above frob_text() for the layout diagram.
> +        */
> +       if (mod) {
> +               if (!within(addr, init_base + init_text_size,
> +                           init_ro_after_init_size - init_text_size)
> +                   && !within(addr, core_base + core_text_size,
> +                              core_ro_after_init_size - core_text_size))
> +                       mod = NULL;
> +       }
> +       return mod;
> +}
> +EXPORT_SYMBOL_GPL(__module_ro_address);
> +
>  /* Don't grab lock, we're oopsing. */
>  void print_modules(void)
>  {
> --
> 2.12.0



-- 
Kees Cook
Pixel Security