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

Jessica Yu
2017-03-30T03:31:30Z

+++ 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@chromium.org>
>Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>

Thanks for the respin, this looks much better.

Acked-by: Jessica Yu <jeyu@redhat.com>

>---
>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
>