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Date: Mon, 13 Feb 2017 10:13:15 -0800
From: Kees Cook <keescook@...omium.org>
To: Eddie Kovsky <ewk@...ovsky.org>
Cc: Jessica Yu <jeyu@...hat.com>, Rusty Russell <rusty@...tcorp.com.au>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC] [PATCH 1/2] module: verify address is read-only
On Sun, Feb 12, 2017 at 3:31 PM, Eddie Kovsky <ewk@...ovsky.org> 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.
>
> Signed-off-by: Eddie Kovsky <ewk@...ovsky.org>
> ---
> include/linux/module.h | 2 ++
> kernel/module.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 46 insertions(+)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 0297c5cd7cdf..2848416f7715 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_ro_address(unsigned long addr);
> bool is_module_percpu_address(unsigned long addr);
> bool is_module_text_address(unsigned long addr);
This will need the !CONFIG_MODULES stubs added as well (see
__module_address()). e.g.:
...
#else /* !CONFIG_MODULES... */
...
static incline struct module *__module_ro_address(unsigned long addr)
{
return NULL;
}
...
#endif
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 8168eb738f4d..e7eb329c585d 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -4270,6 +4270,50 @@ struct module *__module_text_address(unsigned long addr)
> }
> EXPORT_SYMBOL_GPL(__module_text_address);
>
> +/**
> + * is_module_text_ro_address - is this address inside read-only module code?
> + * @addr: the address to check.
> + *
> + */
> +bool is_module_ro_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 code contains a read-only 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);
> +
> + if (mod) {
> + /* Make sure it's within the read-only section. */
> + if (!within(addr, mod->init_layout.base,
> + mod->init_layout.ro_size)
> + && !within(addr, mod->core_layout.base,
> + mod->core_layout.ro_size))
> + mod = NULL;
> + if (!within(addr, mod->init_layout.base,
> + mod->init_layout.ro_after_init_size)
> + && !within(addr, mod->core_layout.base,
> + mod->core_layout.ro_after_init_size))
> + mod = NULL;
> + }
> + return mod;
> +}
> +EXPORT_SYMBOL_GPL(__module_ro_address);
This follows what is_module_address() does, so that seems sensible to
me. I defer to Jessica and Rusty, though. :)
-Kees
--
Kees Cook
Pixel Security
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