[PATCH] elf: Add tests for working RELRO protection

[Florian Weimer <fweimer at redhat dot com>]

(I need to rework the RELRO handling to address the rseq initialization
issue.  Tested on i686-linux-gnu, x86_64-linux-gnu,
powerpc64le-linux-gnu, aarch64-linux-gnu, s390x-linux-gnu.  (The test
does not exercise partial RELRO support, so there's no issue on s390x.)
Build-tested on i686-gnu.  If approved, I will commit the support bits
separately, for easier backporting.)

2019-10-02  Florian Weimer  <fweimer@redhat.com>

	elf: Add tests for working RELRO protection.
	* elf/Makefile [$(build-shared)] (tests): Add tst-relro-shared.
	[$(have-fpie) && $(build-shared)] (tests, tests-pie): Add
	tst-relro-shared-pie.
	(tst-relro-shared, tst-relro-shared-pie): Link with -ldl.
	(LDFLAGS-tst-relro-shared, LDFLAGS-tst-relro-shared-pie): Link
	with -z relro.
	(tst-relro-shared-no-pie): Set to disable PIE for
	tst-relro-shared.
	(CFLAGS-tst-relro-shared-pie.c): Build with -fpie.
	* elf/tst-relro-shared.c: New file.
	* elf/tst-relro-shared-pie.c: Likewise.
	* support/Makefile (libsupport-routines): Add
	support_disable_more_coredumps, support_check_fault_write.
	(tests): Add tst-support_check_fault.
	* support/support.h (support_disable_more_coredumps): Declare.
	* support/check_fault.h: New file.
	* support/support_check_fault_write.c: Likewise.
	* support/support_disable_more_coredumps.c: Likewise.
	* support/tst-support_check_fault.c: Likewise.
	* sysdeps/mach/hurd/support_disable_more_coredumps.c: Likewise.

diff --git a/elf/Makefile b/elf/Makefile
index 8f962991a3..9c696e42a8 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -192,7 +192,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \
 	 tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note \
 	 tst-unwind-ctor tst-unwind-main tst-audit13 \
-	 tst-sonamemove-link tst-sonamemove-dlopen tst-dlopen-aout
+	 tst-sonamemove-link tst-sonamemove-dlopen tst-dlopen-aout \
+	 tst-relro-shared
 #	 reldep9
 tests-internal += loadtest unload unload2 circleload1 \
 	 neededtest neededtest2 neededtest3 neededtest4 \
@@ -308,8 +309,8 @@ test-xfail-tst-protected1b = yes
 endif
 ifeq (yesyes,$(have-fpie)$(build-shared))
 modules-names += tst-piemod1
-tests += tst-pie1 tst-pie2 tst-dlopen-pie
-tests-pie += tst-pie1 tst-pie2
+tests += tst-pie1 tst-pie2 tst-dlopen-pie tst-relro-shared-pie
+tests-pie += tst-pie1 tst-pie2 tst-relro-shared-pie
 ifeq (yes,$(have-protected-data))
 tests += vismain
 tests-pie += vismain
@@ -1270,6 +1271,12 @@ $(objpfx)tst-thrlock: $(libdl) $(shared-thread-library)
 $(objpfx)tst-dlopen-aout: $(libdl) $(shared-thread-library)
 $(objpfx)tst-dlopen-aout-container: $(libdl) $(shared-thread-library)
 LDFLAGS-tst-dlopen-aout-container += -Wl,-rpath,\$$ORIGIN
+$(objpfx)tst-relro-shared: $(libdl)
+LDFLAGS-tst-relro-shared += $(relro-LDFLAGS)
+tst-relro-shared-no-pie = yes
+CFLAGS-tst-relro-shared-pie.c += $(pie-ccflag)
+$(objpfx)tst-relro-shared-pie: $(libdl)
+LDFLAGS-tst-relro-shared-pie += $(relro-LDFLAGS)
 
 CFLAGS-ifuncmain1pic.c += $(pic-ccflag)
 CFLAGS-ifuncmain1picstatic.c += $(pic-ccflag)
diff --git a/elf/tst-relro-shared-pie.c b/elf/tst-relro-shared-pie.c
new file mode 100644
index 0000000000..64f3dfcf45
--- /dev/null
+++ b/elf/tst-relro-shared-pie.c
@@ -0,0 +1,19 @@
+/* Test that RELRO is applied to the program, ld.so, libc.so.  PIE version.
+   Copyright (C) 2019 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 "tst-relro-shared.c"
diff --git a/elf/tst-relro-shared.c b/elf/tst-relro-shared.c
new file mode 100644
index 0000000000..e906fd7fa5
--- /dev/null
+++ b/elf/tst-relro-shared.c
@@ -0,0 +1,64 @@
+/* Test that RELRO protection is applied to the program, ld.so, libc.so.
+   Copyright (C) 2019 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 <gnu/lib-names.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check_fault.h>
+#include <support/xdlfcn.h>
+
+static void (*const global_function_pointer) (void *) = free;
+
+static int
+do_test (void)
+{
+  printf ("info: checking global_function_pointer (%p)\n",
+          &global_function_pointer);
+  support_check_fault_write (&global_function_pointer,
+                             sizeof (global_function_pointer));
+
+  /* Use dlsym to avoid creating copy relocations.  */
+
+  /* This comes from ld.so.  */
+  void *ptr = xdlsym (NULL, "_rtld_global_ro");
+  printf ("info: checking _rtld_global_ro (%p)\n", ptr);
+  /* First byte is _dl_debug_mask, so overwriting that should be
+     relatively harmless (and not cause a crash on its own).  */
+  support_check_fault_write (ptr, 1);
+
+  /* This comes from libc.so.  */
+  ptr = xdlsym (NULL, "_nl_default_dirname");
+  printf ("info: checking _nl_default_dirname (%p)\n", ptr);
+  support_check_fault_write (ptr, 1);
+
+  /* Load libc.so into a new namespace and check that as well. */
+
+  void *new_libc = xdlmopen (LM_ID_NEWLM, LIBC_SO, RTLD_NOW);
+  ptr = xdlsym (new_libc, "_rtld_global_ro");
+  printf ("info: checking _rtld_global_ro in namespace (%p)\n", ptr);
+  support_check_fault_write (ptr, 1);
+  ptr = xdlsym (new_libc, "_nl_default_dirname");
+  printf ("info: checking _nl_default_dirname in namespace (%p)\n", ptr);
+  support_check_fault_write (ptr, 1);
+
+  xdlclose (new_libc);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/support/Makefile b/support/Makefile
index ca238ee8b4..58ea1b974d 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -43,10 +43,12 @@ libsupport-routines = \
   support_can_chroot \
   support_capture_subprocess \
   support_capture_subprocess_check \
+  support_check_fault_write \
   support_chroot \
   support_copy_file_range \
   support_descriptor_supports_holes \
   support_descriptors \
+  support_disable_more_coredumps \
   support_enter_mount_namespace \
   support_enter_network_namespace \
   support_format_address_family \
@@ -218,6 +220,7 @@ tests = \
   tst-support-namespace \
   tst-support_blob_repeat \
   tst-support_capture_subprocess \
+  tst-support_check_fault \
   tst-support_descriptors \
   tst-support_format_dns_packet \
   tst-support_quote_blob \
diff --git a/support/check_fault.h b/support/check_fault.h
new file mode 100644
index 0000000000..03d5c7f41d
--- /dev/null
+++ b/support/check_fault.h
@@ -0,0 +1,29 @@
+/* Check for faults at specific addresses.
+   Copyright (C) 2019 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/>.  */
+
+#ifndef SUPPORT_CHECK_FAULT_H
+#define SUPPORT_CHECK_FAULT_H
+
+#include <stddef.h>
+
+/* Check that write access to SIZE individual bytes starting at
+   address results in SIGSEGV or SIGBUS signal.  Both signals must not
+   be blocked and must have SIG_DFL disposition.  */
+void support_check_fault_write (const void *address, size_t size);
+
+#endif /* SUPPORT_CHECK_FAULT_H */
diff --git a/support/support.h b/support/support.h
index a9df6e9a3c..5677a8e682 100644
--- a/support/support.h
+++ b/support/support.h
@@ -80,6 +80,11 @@ char *support_quote_string (const char *);
    regular file open for writing, and initially empty.  */
 int support_descriptor_supports_holes (int fd);
 
+/* For performance reasons, some tests need to disable all coredumps
+   (not just those which are written to the source directory, which
+   are disabled by the test driver).  */
+void support_disable_more_coredumps (void);
+
 /* Error-checking wrapper functions which terminate the process on
    error.  */
 
diff --git a/support/support_check_fault_write.c b/support/support_check_fault_write.c
new file mode 100644
index 0000000000..e3497863b6
--- /dev/null
+++ b/support/support_check_fault_write.c
@@ -0,0 +1,72 @@
+/* Check for faults at specific addresses.
+   Copyright (C) 2019 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 <support/check_fault.h>
+
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/xunistd.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+/* Probe once at ADDRESS.  Use START and INDEX in error reporting.  */
+static bool
+check_one_address (volatile char *address, const void *start, size_t index)
+{
+  pid_t pid = xfork ();
+  if (pid == 0)
+    {
+      support_disable_more_coredumps ();
+      *address = 0xcc;  /* Try to write an arbitrary value.  */
+      _exit (0);
+    }
+  int status;
+  xwaitpid (pid, &status, 0);
+  if (WIFSIGNALED (status))
+    {
+      if (WTERMSIG (status) != SIGSEGV && WTERMSIG (status) != SIGBUS)
+        {
+          support_record_failure ();
+          printf ("error: unexpected signal %d at %p (%p+%zu)\n",
+                  WTERMSIG (status), address, start, index);
+          return false;
+        }
+    }
+  else
+    {
+      support_record_failure ();
+      printf ("error: missing fault at %p (%p+%zu)\n",
+              address, start, index);
+      return false;
+    }
+  return true;
+}
+
+void
+support_check_fault_write (const void *address, size_t size)
+{
+  TEST_VERIFY (address != NULL);
+  TEST_VERIFY (size > 0);
+
+  for (size_t i = 0; i < size; ++i)
+    if (!check_one_address (((char *) address) + i, address, i))
+      break;
+}
diff --git a/support/support_disable_more_coredumps.c b/support/support_disable_more_coredumps.c
new file mode 100644
index 0000000000..954f16027b
--- /dev/null
+++ b/support/support_disable_more_coredumps.c
@@ -0,0 +1,28 @@
+/* Disable additional coredumps.  Version using <sys/prctl.h>.
+   Copyright (C) 2019 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 <support/check.h>
+#include <support/support.h>
+#include <sys/prctl.h>
+
+void
+support_disable_more_coredumps (void)
+{
+  if (prctl (PR_SET_DUMPABLE, 0, 0, 0, 0) != 0)
+    FAIL_EXIT1 ("prctl (PR_SET_DUMPABLE) failure: %m");
+}
diff --git a/support/tst-support_check_fault.c b/support/tst-support_check_fault.c
new file mode 100644
index 0000000000..8a6b6d9825
--- /dev/null
+++ b/support/tst-support_check_fault.c
@@ -0,0 +1,118 @@
+/* Tests for support_fault_check_write.
+   Copyright (C) 2019 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 <support/check_fault.h>
+
+#include <array_length.h>
+#include <stdlib.h>
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/xunistd.h>
+#include <sys/mman.h>
+
+static void
+check_fault_two_bytes (void *address)
+{
+  support_check_fault_write (address, 2);
+}
+
+static int
+do_test (void)
+{
+  size_t page_size = xsysconf (_SC_PAGESIZE);
+
+  /* Tests with PROT_NONE, PROT_READ and PROT_EXEC are expected to
+     succeed.  */
+  {
+    static const int prots[] = { PROT_NONE, PROT_READ, PROT_EXEC };
+    for (int i = 0; i < array_length (prots); ++i)
+      {
+        void *ptr = xmmap (NULL, 2, prots[i], MAP_PRIVATE | MAP_ANONYMOUS, -1);
+        support_check_fault_write (ptr, 2);
+        xmunmap (ptr, 2);
+      }
+  }
+
+  /* Do not call support_record_failure_reset below if the process has
+     already failed.  */
+  int is_failed = support_record_failure_is_failed ();
+
+  /* Check that the lack of a fault for regular memory is reported at
+     the fist byte.  */
+  {
+    void *ptr = xmalloc (2);
+    struct support_capture_subprocess proc
+      = support_capture_subprocess (check_fault_two_bytes, ptr);
+    support_capture_subprocess_check (&proc, "malloc", 0, sc_allow_stdout);
+    if (!is_failed)
+      support_record_failure_reset ();
+    char *expected = xasprintf ("error: missing fault at %p (%p+0)\n",
+                                ptr, ptr);
+    TEST_COMPARE_STRING (proc.out.buffer, expected);
+    free (expected);
+    support_capture_subprocess_free (&proc);
+    free (ptr);
+  }
+
+  /* Check that a fault only at the first byte results in an error.
+     The probe range crosses a page boundary.  */
+  is_failed = support_record_failure_is_failed ();
+  {
+    char *ptr = xmmap (NULL, 2 * page_size, PROT_READ | PROT_WRITE,
+                       MAP_PRIVATE | MAP_ANONYMOUS, -1);
+    xmprotect (ptr, page_size, PROT_READ);
+    struct support_capture_subprocess proc
+      = support_capture_subprocess (check_fault_two_bytes,
+                                    ptr + page_size - 1);
+    support_capture_subprocess_check (&proc, "R, RW", 0, sc_allow_stdout);
+    if (!is_failed)
+      support_record_failure_reset ();
+    char *expected = xasprintf ("error: missing fault at %p (%p+1)\n",
+                                ptr + page_size, ptr + page_size - 1);
+    TEST_COMPARE_STRING (proc.out.buffer, expected);
+    free (expected);
+    support_capture_subprocess_free (&proc);
+    xmunmap (ptr, 2 * page_size);
+  }
+
+  /* Check that a fault only at the second byte results in an error.
+     Again, the probe range crosses a page boundary.  */
+  is_failed = support_record_failure_is_failed ();
+  {
+    char *ptr = xmmap (NULL, 2 * page_size, PROT_READ | PROT_WRITE,
+                       MAP_PRIVATE | MAP_ANONYMOUS, -1);
+    xmprotect (ptr + page_size, page_size, PROT_READ);
+    struct support_capture_subprocess proc
+      = support_capture_subprocess (check_fault_two_bytes,
+                                    ptr + page_size - 1);
+    support_capture_subprocess_check (&proc, "RW, R", 0, sc_allow_stdout);
+    if (!is_failed)
+      support_record_failure_reset ();
+    char *expected = xasprintf ("error: missing fault at %p (%p+0)\n",
+                                ptr + page_size - 1, ptr + page_size - 1);
+    TEST_COMPARE_STRING (proc.out.buffer, expected);
+    free (expected);
+    support_capture_subprocess_free (&proc);
+    xmunmap (ptr, 2 * page_size);
+  }
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/mach/hurd/support_disable_more_coredumps.c b/sysdeps/mach/hurd/support_disable_more_coredumps.c
new file mode 100644
index 0000000000..fe0fdcc89a
--- /dev/null
+++ b/sysdeps/mach/hurd/support_disable_more_coredumps.c
@@ -0,0 +1,25 @@
+/* Disable additional coredumps.  Hurd version.
+   Copyright (C) 2019 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 <support/support.h>
+
+void
+support_disable_more_coredumps (void)
+{
+  /* Hurd does not have any additional coredumps to disable.  */
+}