[RESEND RFC] kernel/ksysfs.c: restrict /sys/kernel/notes to root access

[Guixiong Wei <guixiongwei@gmail.com>]

From: Guixiong Wei <weiguixiong@bytedance.com>

Restrict non-privileged user access to /sys/kernel/notes to
avoid security attack.

The non-privileged users have read access to notes. The notes
expose the load address of startup_xen. This address could be
used to bypass KASLR.

For example, the startup_xen is built at 0xffffffff82465180 and
commit_creds is built at 0xffffffff810ad570 which could read from
the /boot/System.map. And the loaded address of startup_xen is
0xffffffffbc265180 which read from /sys/kernel/notes. So the loaded
address of commit_creds is 0xffffffffbc265180 - (0xffffffff82465180
 - 0xffffffff810ad570) = 0xffffffffbaead570.

Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com>
---
 kernel/ksysfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index b1292a57c2a5..09bc0730239b 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -199,7 +199,7 @@ static ssize_t notes_read(struct file *filp, struct kobject *kobj,
 static struct bin_attribute notes_attr __ro_after_init  = {
 	.attr = {
 		.name = "notes",
-		.mode = S_IRUGO,
+		.mode = S_IRUSR,
 	},
 	.read = &notes_read,
 };
-- 
2.24.3 (Apple Git-128)