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

olsajiri · torvalds · commit df04abfd181a · 2016-09-20T13:32:49.000-07:00
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 <sbest@redhat.com> Fixes: f5509cc ("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>
diff --git 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
