livepatch: Cleanup module page permission changes

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.
Suggested-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
(cherry picked from commit b56b36ee)
Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

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->core_layout.base;
 	unsigned long core_size = mod->core_layout.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_layout.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);
 }

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
@@ -232,7 +233,7 @@ 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;
 	unsigned long val;
 	struct klp_reloc *reloc;
 
@@ -242,13 +243,16 @@ static int klp_write_object_relocations(struct module *pmod,
 	if (WARN_ON(!obj->relocs))
 		return -EINVAL;
 
+	module_disable_ro(pmod);
+
 	for (reloc = obj->relocs; reloc->name; reloc++) {
 		/* discover the address of the referenced symbol */
 		if (reloc->external) {
 			if (reloc->sympos > 0) {
 				pr_err("non-zero sympos for external reloc symbol '%s' is not supported\n",
 				       reloc->name);
-				return -EINVAL;
+				ret = -EINVAL;
+				goto out;
 			}
 			ret = klp_find_external_symbol(pmod, reloc->name, &val);
 		} else
@@ -257,18 +261,20 @@ static int klp_write_object_relocations(struct module *pmod,
 						     reloc->sympos,
 						     &val);
 		if (ret)
-			return ret;
+			goto out;
 
 		ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
 					     val + reloc->addend);
 		if (ret) {
 			pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
 			       reloc->name, val, ret);
-			return ret;
+			goto out;
 		}
 	}
 
-	return 0;
+out:
+	module_enable_ro(pmod);
+	return ret;
 }
 
 static void notrace klp_ftrace_handler(unsigned long ip,