Re: [PATCH v4 1/2] module: verify address is read-only

[Jessica Yu]

+++ Eddie Kovsky [26/03/17 15:08 -0600]:
> Implement a mechanism to check if a module's address is in
> the rodata or ro_after_init sections. It mimics the existing 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 address is in a read-only section. The idea is to prevent structures
> (including modules) that are not read-only from being passed to functions.
>
> This implements the first half of a suggestion made by Kees Cook for
> the Kernel Self Protection Project:
>
>    - provide mechanism to check for ro_after_init memory areas, and
>      reject structures not marked ro_after_init in vmbus_register()
>
> Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Eddie Kovsky <ewk@xxxxxxxxxxxx>

Thanks for the respin, this looks much better.

Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

> ---
> Changes in v4:
> - Rename function __module_ro_address() to __module_rodata_address()
> - Move module_rodata_address() stub below is_module_address()
> - Minor comment fixes
> - Verify that mod is not NULL before setting up layout variables
> 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..a3d17b081de3 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_rodata_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 +648,11 @@ static inline struct module *__module_address(unsigned long addr)
> 	return NULL;
> }
>
> +static inline struct module *__module_rodata_address(unsigned long addr)
> +{
> +	return NULL;
> +}
> +
> static inline struct module *__module_text_address(unsigned long addr)
> {
> 	return NULL;
> @@ -656,6 +663,11 @@ static inline bool is_module_address(unsigned long addr)
> 	return false;
> }
>
> +static inline bool is_module_rodata_address(unsigned long addr)
> +{
> +	return false;
> +}
> +
> static inline bool is_module_percpu_address(unsigned long addr)
> {
> 	return false;
> diff --git a/kernel/module.c b/kernel/module.c
> index 8ffcd29a4245..26bd62c61d87 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 data?
> + * @addr: the address to check.
> + *
> + */
> +bool is_module_rodata_address(unsigned long addr)
> +{
> +	bool ret;
> +
> +	preempt_disable();
> +	ret = __module_rodata_address(addr) != NULL;
> +	preempt_enable();
> +
> +	return ret;
> +}
> +
> +/*
> + * __module_rodata_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_rodata_address(unsigned long addr)
> +{
> +	struct module *mod = __module_address(addr);
> +
> +	/*
> +	 * 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) {
> +		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;
> +
> +		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_rodata_address);
> +
> /* Don't grab lock, we're oopsing. */
> void print_modules(void)
> {
> --
> 2.12.1