[PATCH 1/2] kallsyms: Hide layout

[Kristen Carlson Accardi]

This patch makes /proc/kallsyms display in a random order, rather
than sorted by address in order to hide the newly randomized address
layout.

Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Tested-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 kernel/kallsyms.c | 117 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 117 insertions(+)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 16c8c605f4b0..7e4939b9ed61 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -25,6 +25,7 @@
 #include <linux/filter.h>
 #include <linux/ftrace.h>
 #include <linux/compiler.h>
+#include <linux/list_sort.h>
 
 /*
  * These will be re-linked against their real values
@@ -446,6 +447,17 @@ struct kallsym_iter {
 	int show_value;
 };
 
+struct kallsyms_iter_list {
+	struct kallsym_iter iter;
+	struct list_head next;
+};
+
+struct kallsyms_sorted_iter {
+	struct kallsym_iter iter;
+	loff_t total_syms;
+	loff_t shuffled_index[];
+};
+
 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
 			    char *type, char *name)
 {
@@ -660,6 +672,110 @@ int kallsyms_show_value(void)
 	}
 }
 
+static void *sorted_start(struct seq_file *m, loff_t *pos)
+{
+	struct kallsyms_sorted_iter *s_iter = m->private;
+
+	if (*pos >= s_iter->total_syms)
+		return NULL;
+
+	return s_start(m, &s_iter->shuffled_index[*pos]);
+}
+
+static void *sorted_next(struct seq_file *m, void *p, loff_t *pos)
+{
+	struct kallsyms_sorted_iter *s_iter = m->private;
+
+	(*pos)++;
+
+	if (*pos >= s_iter->total_syms)
+		return NULL;
+
+	if (!update_iter(m->private, s_iter->shuffled_index[*pos]))
+		return NULL;
+
+	return p;
+}
+
+static const struct seq_operations kallsyms_sorted_op = {
+	.start = sorted_start,
+	.next = sorted_next,
+	.stop = s_stop,
+	.show = s_show
+};
+
+/*
+ * shuffle_text_list()
+ * Use a Fisher Yates algorithm to shuffle a list of text sections.
+ */
+static void shuffle_index_list(loff_t *indexes, int size)
+{
+	int i;
+	unsigned int j;
+	loff_t temp;
+
+	for (i = size - 1; i > 0; i--) {
+		/* pick a random index from 0 to i */
+		get_random_bytes(&j, sizeof(j));
+		j = j % (i + 1);
+
+		temp = indexes[i];
+		indexes[i] = indexes[j];
+		indexes[j] = temp;
+	}
+}
+
+#if defined(CONFIG_FG_KASLR)
+/*
+ * When fine grained kaslr is enabled, we need to
+ * print out the symbols sorted by name rather than by
+ * by address, because this reveals the randomization order.
+ */
+static int kallsyms_open(struct inode *inode, struct file *file)
+{
+	loff_t pos;
+	struct kallsyms_sorted_iter *sorted_iter;
+	struct kallsym_iter iter;
+
+	/*
+	 * we need to figure out how many extra symbols there are
+	 * to print out past kallsyms_num_syms
+	 */
+	pos = kallsyms_num_syms;
+	reset_iter(&iter, 0);
+	do {
+		if (!update_iter(&iter, pos))
+			break;
+		pos++;
+	} while (1);
+
+	/*
+	 * add storage space for an array of loff_t equal to the size
+	 * of the total number of symbols we need to print
+	 */
+	sorted_iter = __seq_open_private(file, &kallsyms_sorted_op,
+					 sizeof(*sorted_iter) +
+					 (sizeof(pos) * pos));
+	if (!sorted_iter)
+		return -ENOMEM;
+
+	reset_iter(&sorted_iter->iter, 0);
+	sorted_iter->iter.show_value = kallsyms_show_value();
+	sorted_iter->total_syms = pos;
+
+	/*
+	 * initialize the array with all possible pos values, then
+	 * shuffle the array so that the values will display in a
random
+	 * order.
+	 */
+	for (pos = 0; pos < sorted_iter->total_syms; pos++)
+		sorted_iter->shuffled_index[pos] = pos;
+
+	shuffle_index_list(sorted_iter->shuffled_index, sorted_iter-
>total_syms);
+
+	return 0;
+}
+#else
 static int kallsyms_open(struct inode *inode, struct file *file)
 {
 	/*
@@ -676,6 +792,7 @@ static int kallsyms_open(struct inode *inode,
struct file *file)
 	iter->show_value = kallsyms_show_value();
 	return 0;
 }
+#endif /* CONFIG_FG_KASLR */
 
 #ifdef	CONFIG_KGDB_KDB
 const char *kdb_walk_kallsyms(loff_t *pos)
-- 
2.20.1