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

[Josh Poimboeuf]

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@xxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 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

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