[PATCH] fs/proc/kcore.c: Omit kernel text area for hardened usercopy feature

[Jiri Olsa]

One of the bullets for hardened usercopy feature is:
  - object must not overlap with kernel text

which is what we expose via /proc/kcore. We can hit
this check and crash the system very easily just by
reading the text area in kcore file:

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

Omitting kernel text area from kcore when there's
hardened usercopy feature is enabled.

Fixes: f5509cc18daa ("mm: Hardened usercopy")
Reported-by: Steve Best <sbest@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 fs/proc/kcore.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index a939f5ed7f89..e322d4e0be4d 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -629,8 +629,12 @@ static int __init proc_kcore_init(void)
 		pr_err("couldn't create /proc/kcore\n");
 		return 0; /* Always returns 0. */
 	}
+
+#ifndef CONFIG_HARDENED_USERCOPY
 	/* Store text area if it's special */
 	proc_kcore_text_init();
+#endif
+
 	/* Store vmalloc area */
 	kclist_add(&kcore_vmalloc, (void *)VMALLOC_START,
 		VMALLOC_END - VMALLOC_START, KCORE_VMALLOC);
-- 
2.7.4