printk: use %pK for /proc/kallsyms and /proc/modules

In an effort to reduce kernel address leaks that might be used to help
target kernel privilege escalation exploits, this patch uses %pK when
displaying addresses in /proc/kallsyms, /proc/modules, and
/sys/module/*/sections/*.

Note that this changes %x to %p, so some legitimately 0 values in
/proc/kallsyms would have changed from 00000000 to "(null)".  To avoid
this, "(null)" is not used when using the "K" format.  Anything that was
already successfully parsing "(null)" in addition to full hex digits
should have no problem with this change.  (Thanks to Joe Perches for the
suggestion.) Due to the %x to %p, "void *" casts are needed since these
addresses are already "unsigned long" everywhere internally, due to their
starting life as ELF section offsets.

Signed-off-by: Kees Cook <kees.cook@canonical.com>
Cc: Eugene Teo <eugene@redhat.com>
Cc: Dan Rosenberg <drosenberg@vsecurity.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 6 insertions, 8 deletions

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 6f6d091b5757..75dcca37d61a 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -477,13 +477,11 @@ static int s_show(struct seq_file *m, void *p)
                  */
                 type = iter->exported ? toupper(iter->type) :
                                         tolower(iter->type);
-                seq_printf(m, "%0*lx %c %s\t[%s]\n",
-                           (int)(2 * sizeof(void *)),
-                           iter->value, type, iter->name, iter->module_name);
+                seq_printf(m, "%pK %c %s\t[%s]\n", (void *)iter->value,
+                           type, iter->name, iter->module_name);
         } else
-                seq_printf(m, "%0*lx %c %s\n",
-                           (int)(2 * sizeof(void *)),
-                           iter->value, iter->type, iter->name);
+                seq_printf(m, "%pK %c %s\n", (void *)iter->value,
+                           iter->type, iter->name);
         return 0;
 }
 
diff --git a/kernel/module.c b/kernel/module.c
index efa290ea94bf..1f9f7bc56ca1 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1168,7 +1168,7 @@ static ssize_t module_sect_show(struct module_attribute *mattr,
 {
         struct module_sect_attr *sattr =
                 container_of(mattr, struct module_sect_attr, mattr);
-        return sprintf(buf, "0x%lx\n", sattr->address);
+        return sprintf(buf, "0x%pK\n", (void *)sattr->address);
 }
 
 static void free_sect_attrs(struct module_sect_attrs *sect_attrs)
@@ -3224,7 +3224,7 @@ static int m_show(struct seq_file *m, void *p)
                    mod->state == MODULE_STATE_COMING ? "Loading":
                    "Live");
         /* Used by oprofile and other similar tools. */
-        seq_printf(m, " 0x%p", mod->module_core);
+        seq_printf(m, " 0x%pK", mod->module_core);
 
         /* Taints info */
         if (mod->taints)