[PATCH v3] use %pK for /proc/kallsyms and /proc/modules

[PATCH v3] use %pK for /proc/kallsyms and /proc/modules

[Kees Cook]

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>
---
v2:
 - ditch %0* with 2*sizeof(void*) prefixing since %p is already rendered
   to that width, thanks to Joe Perches.
v3:
 - add "void *" casts to avoid -Wformat warnings.
---
 kernel/kallsyms.c |   10 ++++------
 kernel/module.c   |    4 ++--
 lib/vsprintf.c    |    2 +-
 3 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 6f6d091..75dcca3 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 34e00b7..54e76a7 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)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d3023df..288d770 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -991,7 +991,7 @@ static noinline_for_stack
 char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	      struct printf_spec spec)
 {
-	if (!ptr) {
+	if (!ptr && *fmt != 'K') {
 		/*
 		 * Print (null) with the same width as a pointer so it makes
 		 * tabular output look nice.
-- 
1.7.2.3

-- 
Kees Cook
Ubuntu Security Team