[PATCH 8/9] kallsyms: hide layout

[Kristen Carlson Accardi]

To support finer grained kaslr (fgkaslr), we need to hide our sorted
list of symbols, since this will give away our new layout.
This patch makes /proc/kallsyms only visible to priviledged users.

Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
---
 kernel/kallsyms.c | 138 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 137 insertions(+), 1 deletion(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 16c8c605f4b0..861972b6a879 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 +447,11 @@ struct kallsym_iter {
 	int show_value;
 };
 
+struct kallsyms_iter_list {
+	struct kallsym_iter iter;
+	struct list_head next;
+};
+
 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
 			    char *type, char *name)
 {
@@ -660,6 +666,121 @@ int kallsyms_show_value(void)
 	}
 }
 
+static int sorted_show(struct seq_file *m, void *p)
+{
+	struct list_head *list = m->private;
+	struct kallsyms_iter_list *iter;
+	int rc;
+
+	if (list_empty(list))
+		return 0;
+
+	iter = list_first_entry(list, struct kallsyms_iter_list, next);
+
+	m->private = iter;
+	rc = s_show(m, p);
+	m->private = list;
+
+	list_del(&iter->next);
+	kfree(iter);
+
+	return rc;
+}
+
+static void *sorted_start(struct seq_file *m, loff_t *pos)
+{
+	return m->private;
+}
+
+static void *sorted_next(struct seq_file *m, void *p, loff_t *pos)
+{
+	struct list_head *list = m->private;
+
+	(*pos)++;
+
+	if (list_empty(list))
+		return NULL;
+
+	return p;
+}
+
+static const struct seq_operations kallsyms_sorted_op = {
+	.start = sorted_start,
+	.next = sorted_next,
+	.stop = s_stop,
+	.show = sorted_show
+};
+
+static int kallsyms_list_cmp(void *priv, struct list_head *a,
+				struct list_head *b)
+{
+	struct kallsyms_iter_list *iter_a, *iter_b;
+
+	iter_a = list_entry(a, struct kallsyms_iter_list, next);
+	iter_b = list_entry(b, struct kallsyms_iter_list, next);
+
+	return strcmp(iter_a->iter.name, iter_b->iter.name);
+}
+
+int get_all_symbol_name(void *data, const char *name, struct module *mod,
+			unsigned long addr)
+{
+	unsigned long sym_pos;
+	struct kallsyms_iter_list *node, *last;
+	struct list_head *head = (struct list_head *)data;
+
+	node = kmalloc(sizeof(*node), GFP_KERNEL);
+	if (!node)
+		return -ENOMEM;
+
+	if (list_empty(head)) {
+		sym_pos = 0;
+		memset(node, 0, sizeof(*node));
+		reset_iter(&node->iter, 0);
+		node->iter.show_value = kallsyms_show_value();
+	} else {
+		last = list_first_entry(head, struct kallsyms_iter_list, next);
+		memcpy(node, last, sizeof(*node));
+		sym_pos = last->iter.pos;
+	}
+
+	INIT_LIST_HEAD(&node->next);
+	list_add(&node->next, head);
+
+	/*
+	 * update_iter returns false when at end of file
+	 * which in this case we don't care about and can
+	 * safely ignore. update_iter() will increment
+	 * the value of iter->pos, for ksymbol_core.
+	 */
+	if (sym_pos >= kallsyms_num_syms)
+		sym_pos++;
+
+	(void) update_iter(&node->iter, sym_pos);
+
+	return 0;
+}
+
+static int kallsyms_sorted_open(struct inode *inode, struct file *file)
+{
+	int ret;
+	struct list_head *list;
+
+	list = __seq_open_private(file, &kallsyms_sorted_op, sizeof(*list));
+	if (!list)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(list);
+
+	ret = kallsyms_on_each_symbol(get_all_symbol_name, list);
+	if (ret != 0)
+		return ret;
+
+	list_sort(NULL, list, kallsyms_list_cmp);
+
+	return 0;
+}
+
 static int kallsyms_open(struct inode *inode, struct file *file)
 {
 	/*
@@ -704,9 +825,24 @@ static const struct proc_ops kallsyms_proc_ops = {
 	.proc_release	= seq_release_private,
 };
 
+static const struct proc_ops kallsyms_sorted_proc_ops = {
+	.proc_open = kallsyms_sorted_open,
+	.proc_read = seq_read,
+	.proc_lseek = seq_lseek,
+	.proc_release = seq_release_private,
+};
+
 static int __init kallsyms_init(void)
 {
-	proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
+	/*
+	 * 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.
+	 */
+	if (!IS_ENABLED(CONFIG_FG_KASLR))
+		proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
+	else
+		proc_create("kallsyms", 0444, NULL, &kallsyms_sorted_proc_ops);
 	return 0;
 }
 device_initcall(kallsyms_init);
-- 
2.20.1