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>

2 files changed, 13 insertions, 28 deletions

diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
index bcc06e82a593..92fc1a51f994 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->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);
 }
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 94893e844e44..bc2c85c064c1 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
@@ -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,