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

[Kees Cook]

On Wed, Mar 22, 2017 at 7:55 PM, Eddie Kovsky <ewk@xxxxxxxxxxxx> wrote:
> Provide a mechanism to check if the address of a variable is
> const or ro_after_init. It mimics the existing functions that test if an
> address is inside the kernel's text section.
>
> Other functions inside the kernel could then use this capability to
> verify that their arguments are read-only.
>
> Signed-off-by: Eddie Kovsky <ewk@xxxxxxxxxxxx>

Looks great!

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
> Changes in v3:
>  - Fix missing declaration of is_module_rodata_address()
>
>  include/linux/kernel.h |  2 ++
>  kernel/extable.c       | 29 +++++++++++++++++++++++++++++
>  2 files changed, 31 insertions(+)
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 4c26dc3a8295..51beea39e6c4 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -444,6 +444,8 @@ extern int core_kernel_data(unsigned long addr);
>  extern int __kernel_text_address(unsigned long addr);
>  extern int kernel_text_address(unsigned long addr);
>  extern int func_ptr_is_kernel_text(void *ptr);
> +extern int core_kernel_ro_data(unsigned long addr);
> +extern int kernel_ro_address(unsigned long addr);
>
>  unsigned long int_sqrt(unsigned long);
>
> diff --git a/kernel/extable.c b/kernel/extable.c
> index 2676d7f8baf6..3c3a9f4e6250 100644
> --- a/kernel/extable.c
> +++ b/kernel/extable.c
> @@ -154,3 +154,32 @@ int func_ptr_is_kernel_text(void *ptr)
>                 return 1;
>         return is_module_text_address(addr);
>  }
> +
> +/**
> + * core_kernel_ro_data - Verify address points to read-only section
> + * @addr: address to test
> + *
> + */
> +int core_kernel_ro_data(unsigned long addr)
> +{
> +       if (addr >= (unsigned long)__start_rodata &&
> +           addr < (unsigned long)__end_rodata)
> +               return 1;
> +
> +       if (addr >= (unsigned long)__start_data_ro_after_init &&
> +           addr < (unsigned long)__end_data_ro_after_init)
> +               return 1;
> +
> +       return 0;
> +}
> +
> +/* Verify that address is const or ro_after_init. */
> +int kernel_ro_address(unsigned long addr)
> +{
> +       if (core_kernel_ro_data(addr))
> +               return 1;
> +       if (is_module_rodata_address(addr))
> +               return 1;
> +
> +       return 0;
> +}
> --
> 2.12.0



-- 
Kees Cook
Pixel Security