fs/proc/kcore.c: Add bounce buffer for ktext data

df04abfd · Jiri Olsa <[email protected]> · 2016-09-08 09:57:08 +02:00

We hit hardened usercopy feature check for kernel text access by reading
kcore file:

  usercopy: kernel memory exposure attempt detected from ffffffff8179a01f (<kernel text>) (4065 bytes)
  kernel BUG at mm/usercopy.c:75!

Bypassing this check for kcore by adding bounce buffer for ktext data.

Reported-by: Steve Best <[email protected]>
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Suggested-by: Kees Cook <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Acked-by: Kees Cook <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: df04abfd181acc276ba6762c8206891ae10ae00d
Parents: f5beeb18

Changes

1 files changed · +6 −1

File	Status	Add	Del	Content
fs/proc/kcore.c	modified	+6	−1	View file

fs/proc/kcore.c

View file

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index bd3ac9d..5c89a07 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -509,7 +509,12 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 			if (kern_addr_valid(start)) {
 				unsigned long n;
 
-				n = copy_to_user(buffer, (char *)start, tsz);
+				/*
+				 * Using bounce buffer to bypass the
+				 * hardened user copy kernel text checks.
+				 */
+				memcpy(buf, (char *) start, tsz);
+				n = copy_to_user(buffer, buf, tsz);
 				/*
 				 * We cannot distinguish between fault on source
 				 * and fault on destination. When this happens