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

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 <sbest@redhat.com>
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Bug: 31374226
Change-Id: Ic93e6041b67d804a994518bf4950811f828b406e
(cherry picked from commit df04abfd181acc276ba6762c8206891ae10ae00d)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 2dc8404..21f198a 100644 (file)
--- 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