x86: Remove ARCH_CET_LEGACY_BITMAP [BZ #25397]

Since legacy bitmap doesn't cover jitted code generated by legacy JIT
engine, it isn't very useful.  This patch removes ARCH_CET_LEGACY_BITMAP
and treats indirect branch tracking similar to shadow stack by removing
legacy bitmap support.

Tested on CET Linux/x86-64 and non-CET Linux/x86-64.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 38 insertions, 0 deletions

diff --git a/sysdeps/x86/tst-cet-legacy-7.c b/sysdeps/x86/tst-cet-legacy-7.c
new file mode 100644
index 0000000000..58bcb29a5f
--- /dev/null
+++ b/sysdeps/x86/tst-cet-legacy-7.c
@@ -0,0 +1,38 @@
+/* Check compatibility of legacy executable with a JIT engine.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <sys/mman.h>
+#include <support/xunistd.h>
+
+/* Check that mmapped legacy code works with -fcf-protection=none.  */
+
+static int
+do_test (void)
+{
+  void (*funcp) (void);
+  funcp = xmmap (NULL, 0x1000, PROT_EXEC | PROT_READ | PROT_WRITE,
+		 MAP_ANONYMOUS | MAP_PRIVATE, -1);
+  printf ("mmap = %p\n", funcp);
+  /* Write RET instruction.  */
+  *(char *) funcp = 0xc3;
+  funcp ();
+  return 0;
+}
+
+#include <support/test-driver.c>