+++ Eddie Kovsky [17/02/17 22:58 -0700]:
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.
It would be helpful to explain in the changelog the motivation or
reason we're adding to the current api, and why this is needed.
Signed-off-by: Eddie Kovsky <[email protected]>
---
include/linux/module.h | 7 +++++++
kernel/module.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 51 insertions(+)
diff --git a/include/linux/module.h b/include/linux/module.h
index 0297c5cd7cdf..1608d3570ee2 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);
@@ -645,6 +647,11 @@ static inline struct module *__module_address(unsigned
long addr)
return NULL;
}
+static inline struct module *__module_ro_address(unsigned long addr)
+{
+ return NULL;
+}
+
There needs to be a corresponding !CONFIG_MODULES stub for
is_module_ro_address() as well, see is_module_address(), etc.
static inline struct module *__module_text_address(unsigned long addr)
{
return NULL;
diff --git a/kernel/module.c b/kernel/module.c
index 7eba6dea4f41..298cfe4645b1 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4275,6 +4275,50 @@ 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.
s/is_module_text_ro_address/is_module_ro_address/
Although I would slightly prefer the name is_module_rodata_address, or
something similar, because it's unclear to me (without looking at the
code) whether the function covers text addresses. And we already have
is_module_text_address() for that case.
+ *
+ */
+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.
Maybe we should be more specific in the comment and clarify that we're
getting 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);
+
+ 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 a ro_after_init address gets passed in here, mod will be prematurely
set to NULL here, because it is not within [base, base + ro_size).
See comment above frob_text() in module.c for a module layout "diagram".
Also, starting from layout.base will give us the text region as well,
but we just want to check the rodata/ro_after_init regions, same as
what the kernel counterpart in patch 2/3 does. The rodata region
starts at base + text_size.
So we can just simplify this to just one conditional:
(ugly, but shouldn't look bad when cleaned up with some variables)
if (!within(addr, mod->init_layout.base + mod->init_layout.text_size,
mod->init_layout.ro_after_init_size -
mod->init_layout.text_size)
&& !within(addr, mod->core_layout.base + mod->core_layout.text_size,
mod->core_layout.ro_after_init_size -
mod->core_layout.text_size))
This is because range [base + text_size, base + ro_after_init_size)
encompasses both the rodata and ro_after_init regions.
Jessica
+ 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);
+
/* Don't grab lock, we're oopsing. */
void print_modules(void)
{
--
2.11.1
