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Date: Wed, 22 Mar 2017 20:55:48 -0600
From: Eddie Kovsky <ewk@...ovsky.org>
To: jeyu@...hat.com,
rusty@...tcorp.com.au,
keescook@...omium.org
Cc: linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: [PATCH v3 1/2] module: verify address is read-only
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@...ovsky.org>
---
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
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