[PATCH v2 3/3] livepatch: Cleanup module page permission changes

Josh Poimboeuf
2015-11-05T21:19:48Z

Calling set_memory_rw() and set_memory_ro() for every iteration of the
loop in klp_write_object_relocations() is messy, inefficient, and
error-prone.

Change all the read-only pages to read-write before the loop and convert
them back to read-only again afterwards.

The {un}set_module_core_ro_nx() functions are used to change the
page permissions. Toggling NX isn't necessary in this case, but it's
not highly performance sensitive code so it should be fine.

Suggested-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/kernel/livepatch.c | 25 ++-----------------------
include/linux/module.h | 4 ++++
kernel/livepatch/core.c | 15 ++++++++++-----
kernel/module.c | 6 ++----
4 files changed, 18 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
index d1d35cc..13eaf68 100644
--- a/arch/x86/kernel/livepatch.c
+++ b/arch/x86/kernel/livepatch.c
@@ -20,8 +20,6 @@

#include <linux/module.h>
#include <linux/uaccess.h>
-#include <asm/cacheflush.h>
-#include <asm/page_types.h>
#include <asm/elf.h>
#include <asm/livepatch.h>

@@ -38,8 +36,7 @@
int klp_write_module_reloc(struct module *mod, unsigned long type,
unsigned long loc, unsigned long value)
{
- int ret, numpages, size = 4;
- bool readonly;
+ size_t size = 4;
unsigned long val;
unsigned long core = (unsigned long)mod->module_core;
unsigned long core_size = mod->core_size;
@@ -69,23 +66,5 @@ int klp_write_module_reloc(struct module *mod, unsigned long type,
/* loc does not point to any symbol inside the module */
return -EINVAL;

- readonly = false;
-
-#ifdef CONFIG_DEBUG_SET_MODULE_RONX
- if (loc < core + mod->core_ro_size)
- readonly = true;
-#endif
-
- /* determine if the relocation spans a page boundary */
- numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
-
- if (readonly)
- set_memory_rw(loc & PAGE_MASK, numpages);
-
- ret = probe_kernel_write((void *)loc, &val, size);
-
- if (readonly)
- set_memory_ro(loc & PAGE_MASK, numpages);
-
- return ret;
+ return probe_kernel_write((void *)loc, &val, size);
}
diff --git a/include/linux/module.h b/include/linux/module.h
index 3a19c79..557be36 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -766,9 +766,13 @@ extern int module_sysfs_initialized;
#define __MODULE_STRING(x) __stringify(x)

#ifdef CONFIG_DEBUG_SET_MODULE_RONX
+extern void set_module_core_ro_nx(struct module *mod);
+extern void unset_module_core_ro_nx(struct module *mod);
extern void set_all_modules_text_rw(void);
extern void set_all_modules_text_ro(void);
#else
+static inline void set_module_core_ro_nx(struct module *mod) { }
+static inline void unset_module_core_ro_nx(struct module *mod) { }
static inline void set_all_modules_text_rw(void) { }
static inline void set_all_modules_text_ro(void) { }
#endif
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 6e53441..1c94c4b 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -28,6 +28,7 @@
#include <linux/list.h>
#include <linux/kallsyms.h>
#include <linux/livepatch.h>
+#include <asm/cacheflush.h>

/**
* struct klp_ops - structure for tracking registered ftrace ops structs
@@ -283,7 +284,7 @@ static int klp_find_external_symbol(struct module *pmod, const char *name,
static int klp_write_object_relocations(struct module *pmod,
struct klp_object *obj)
{
- int ret;
+ int ret = 0;
struct klp_reloc *reloc;

if (WARN_ON(!klp_is_object_loaded(obj)))
@@ -292,12 +293,14 @@ static int klp_write_object_relocations(struct module *pmod,
if (WARN_ON(!obj->relocs))
return -EINVAL;

+ unset_module_core_ro_nx(pmod);
+
for (reloc = obj->relocs; reloc->name; reloc++) {
if (!klp_is_module(obj)) {
ret = klp_verify_vmlinux_symbol(reloc->name,
reloc->val);
if (ret)
- return ret;
+ goto out;
} else {
/* module, reloc->val needs to be discovered */
if (reloc->external)
@@ -309,18 +312,20 @@ static int klp_write_object_relocations(struct module *pmod,
reloc->name,
&reloc->val);
if (ret)
- return ret;
+ goto out;
}
ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
reloc->val + reloc->addend);
if (ret) {
pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
reloc->name, reloc->val, ret);
- return ret;
+ goto out;
}
}

- return 0;
+out:
+ set_module_core_ro_nx(pmod);
+ return ret;
}

static void notrace klp_ftrace_handler(unsigned long ip,
diff --git a/kernel/module.c b/kernel/module.c
index 14b2249..eb6a924 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1915,14 +1915,14 @@ static void set_section_ro_nx(void *base,
}
}

-static void set_module_core_ro_nx(struct module *mod)
+void set_module_core_ro_nx(struct module *mod)
{
set_section_ro_nx(mod->module_core, mod->core_text_size,
mod->core_ro_size, mod->core_size,
set_memory_ro, set_memory_nx);
}

-static void unset_module_core_ro_nx(struct module *mod)
+void unset_module_core_ro_nx(struct module *mod)
{
set_section_ro_nx(mod->module_core, mod->core_text_size,
mod->core_ro_size, mod->core_size,
@@ -1989,9 +1989,7 @@ void set_all_modules_text_ro(void)
mutex_unlock(&module_mutex);
}
#else
-static void set_module_core_ro_nx(struct module *mod) { }
static void set_module_init_ro_nx(struct module *mod) { }
-static void unset_module_core_ro_nx(struct module *mod) { }
static void unset_module_init_ro_nx(struct module *mod) { }
#endif

--
2.4.3