* sysdeps/i386/dl-machine.h (RTLD_START): Set __libc_stack_end before

	calling _dl_start, using GOTOFF access.

	* configure.in (libc_cv_z_execstack): New check.
	* configure: Regenerated.
	* config.make.in (have-z-execstack): New variable set by it.
	* elf/tst-execstack.c: New file.
	* elf/tst-execstack-mod.c: New file.
	* elf/tst-execstack-needed.c: New file.
	* elf/Makefile (tests-execstack-yes, modules-execstack-yes): New
	variables.
	(tests, modules-names): Conditionally include them.
	(distribute): Add tst-execstack-mod.c here.
	($(objpfx)tst-execstack, $(objpfx)tst-execstack.out): New targets.
	(LDFLAGS-tst-execstack, LDFLAGS-tst-execstack-mod): New variables.
	($(objpfx)tst-execstack-needed): New target.
	(LDFLAGS-tst-execstack-needed): New variable.

	* sysdeps/generic/ldsodefs.h (struct rtld_global): Add _dl_stack_flags
	and _dl_make_stack_executable_hook.  Declare _dl_make_stack_executable.
	* elf/rtld.c (_rtld_global): Add initializer for _dl_stack_flags.
	(dl_main): Reset _dl_stack_flags according to PT_GNU_STACK phdr.
	Initialize _dl_make_stack_executable_hook.
	* elf/dl-support.c: Define those new variables.
	(_dl_non_dynamic_init): Scan phdrs for PT_GNU_STACK.
	(_dl_phdr): Fix type.
	* elf/dl-load.c (_dl_map_object_from_fd): Grok PT_GNU_STACK phdr and
	enable execute permission for the stack if necessary.
	* sysdeps/generic/dl-execstack.c: New file.
	* elf/Makefile (dl-routines): Add it.
	* elf/Versions (ld: GLIBC_PRIVATE): Add _dl_make_stack_executable.
	* sysdeps/unix/sysv/linux/dl-execstack.c: New file.

4 files changed, 217 insertions, 3 deletions

diff --git a/elf/Makefile b/elf/Makefile
index d5a1c3de34..36f205abb2 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -29,7 +29,8 @@ routines	= $(dl-routines) dl-open dl-close dl-support dl-iteratephdr \
 # profiled libraries.
 dl-routines	= $(addprefix dl-,load cache lookup object reloc deps \
 			          runtime error init fini debug misc \
-				  version profile conflict tls origin)
+				  version profile conflict tls origin \
+				  execstack)
 all-dl-routines = $(dl-routines) $(sysdep-dl-routines)
 # But they are absent from the shared libc, because that code is in ld.so.
 elide-routines.os = $(all-dl-routines) dl-support enbl-secure \
@@ -80,6 +81,7 @@ distribute	:= rtld-Rules \
 		   reldep9.c reldep9mod1.c reldep9mod2.c reldep9mod3.c \
 		   tst-array1.exp tst-array2.exp tst-array4.exp \
 		   tst-array2dep.c \
+		   tst-execstack-mod.c \
 		   check-textrel.c dl-sysdep.h
 
 CFLAGS-dl-runtime.c = -fexceptions -fasynchronous-unwind-tables
@@ -150,12 +152,14 @@ tests += loadtest restest1 preloadtest loadfail multiload origtest resolvfail \
 	 neededtest3 neededtest4 unload2 lateglobal initfirst global \
 	 restest2 next dblload dblunload reldep5 reldep6 reldep7 reldep8 \
 	 circleload1 tst-tls3 tst-tls4 tst-tls5 tst-tls6 tst-tls7 tst-tls8 \
-	 tst-tls10 tst-tls11 tst-tls12 tst-tls13 tst-tls14 tst-align
+	 tst-tls10 tst-tls11 tst-tls12 tst-tls13 tst-tls14 tst-align \
+	 $(tests-execstack-$(have-z-execstack))
 #	 reldep9
 test-srcs = tst-pathopt
 tests-vis-yes = vismain
 tests-nodelete-yes = nodelete nodelete2
 tests-nodlopen-yes = nodlopen nodlopen2
+tests-execstack-yes = tst-execstack tst-execstack-needed
 endif
 modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		testobj1_1 failobj constload2 constload3 unloadmod \
@@ -178,7 +182,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		circlemod3 circlemod3a \
 		reldep8mod1 reldep8mod2 reldep8mod3 \
 		reldep9mod1 reldep9mod2 reldep9mod3 \
-		tst-alignmod
+		tst-alignmod $(modules-execstack-$(have-z-execstack))
 ifeq (yes,$(have-initfini-array))
 modules-names += tst-array2dep
 endif
@@ -186,6 +190,7 @@ modules-vis-yes = vismod1 vismod2 vismod3
 modules-nodelete-yes = nodelmod1 nodelmod2 nodelmod3 nodelmod4 \
 		       nodel2mod1 nodel2mod2 nodel2mod3
 modules-nodlopen-yes = nodlopenmod nodlopenmod2
+modules-execstack-yes = tst-execstack-mod
 extra-objs += $(addsuffix .os,$(strip $(modules-names)))
 # We need this variable to be sure the test modules get the right CPPFLAGS.
 test-extras += $(modules-names)
@@ -660,6 +665,16 @@ $(objpfx)tst-tls9-static: $(common-objpfx)dlfcn/libdl.a
 $(objpfx)tst-tls9-static.out: $(objpfx)tst-tlsmod5.so $(objpfx)tst-tlsmod6.so
 endif
 
+ifeq ($(have-z-execstack),yes)
+$(objpfx)tst-execstack: $(libdl)
+$(objpfx)tst-execstack.out: $(objpfx)tst-execstack-mod.so
+LDFLAGS-tst-execstack = -Wl,-z,noexecstack
+LDFLAGS-tst-execstack-mod = -Wl,-z,execstack
+
+$(objpfx)tst-execstack-needed: $(objpfx)tst-execstack-mod.so
+LDFLAGS-tst-execstack-needed = -Wl,-z,noexecstack
+endif
+
 $(objpfx)tst-array1.out: $(objpfx)tst-array1
 	$(elf-objpfx)$(rtld-installed-name) \
 	  --library-path $(rpath-link)$(patsubst %,:%,$(sysdep-library-path)) \
diff --git a/elf/tst-execstack-mod.c b/elf/tst-execstack-mod.c
new file mode 100644
index 0000000000..038e6550b5
--- /dev/null
+++ b/elf/tst-execstack-mod.c
@@ -0,0 +1,30 @@
+/* Test module for making nonexecutable stacks executable
+   on load of a DSO that requires executable stacks.  */
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void callme (void (*callback) (void));
+
+/* This is a function that makes use of executable stack by
+   using a local function trampoline.  */
+void
+tryme (void)
+{
+  bool ok = false;
+  void callback (void) { ok = true; }
+
+  callme (&callback);
+
+  if (ok)
+    printf ("DSO called ok (local %p, trampoline %p)\n", &ok, &callback);
+  else
+    abort ();
+}
+
+void
+callme (void (*callback) (void))
+{
+  (*callback) ();
+}
diff --git a/elf/tst-execstack-needed.c b/elf/tst-execstack-needed.c
new file mode 100644
index 0000000000..03090f7dd6
--- /dev/null
+++ b/elf/tst-execstack-needed.c
@@ -0,0 +1,36 @@
+/* Test program for making nonexecutable stacks executable
+   on DT_NEEDED load of a DSO that requires executable stacks.  */
+
+#include <dlfcn.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <error.h>
+
+extern void tryme (void);	/* from tst-execstack-mod.so */
+
+static void deeper (void (*f) (void));
+
+static int
+do_test (void)
+{
+  tryme ();
+
+  /* Test that growing the stack region gets new executable pages too.  */
+  deeper (&tryme);
+
+  return 0;
+}
+
+static void
+deeper (void (*f) (void))
+{
+  char stack[1100 * 1024];
+  memfrob (stack, sizeof stack);
+  (*f) ();
+  memfrob (stack, sizeof stack);
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/elf/tst-execstack.c b/elf/tst-execstack.c
new file mode 100644
index 0000000000..21eaa9bc90
--- /dev/null
+++ b/elf/tst-execstack.c
@@ -0,0 +1,133 @@
+/* Test program for making nonexecutable stacks executable
+   on load of a DSO that requires executable stacks.  */
+
+#include <dlfcn.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <error.h>
+
+static void
+print_maps (void)
+{
+#if 0
+  char *cmd = NULL;
+  asprintf (&cmd, "cat /proc/%d/maps", getpid ());
+  system (cmd);
+  free (cmd);
+#endif
+}
+
+static void deeper (void (*f) (void));
+
+#if USE_PTHREADS
+# include <pthread.h>
+
+static void *
+tryme_thread (void *f)
+{
+  (*((void (*) (void)) f)) ();
+
+  return 0;
+}
+
+static pthread_barrier_t startup_barrier, go_barrier;
+static void *
+waiter_thread (void *arg)
+{
+  void **f = arg;
+  pthread_barrier_wait (&startup_barrier);
+  pthread_barrier_wait (&go_barrier);
+
+  (*((void (*) (void)) *f)) ();
+
+  return 0;
+}
+#endif
+
+static int
+do_test (void)
+{
+  void *f;
+
+#if USE_PTHREADS
+  /* Create some threads while stacks are nonexecutable.  */
+  #define N 5
+  pthread_t thr[N];
+
+  pthread_barrier_init (&startup_barrier, NULL, N + 1);
+  pthread_barrier_init (&go_barrier, NULL, N + 1);
+
+  for (int i = 0; i < N; ++i)
+    {
+      int rc = pthread_create (&thr[i], NULL, &waiter_thread, &f);
+      if (rc)
+	error (1, rc, "pthread_create");
+    }
+
+  /* Make sure they are all there using their stacks.  */
+  pthread_barrier_wait (&startup_barrier);
+  puts ("threads waiting");
+#endif
+
+  print_maps ();
+
+  /* Loading this module should force stacks to become executable.  */
+  void *h = dlopen ("tst-execstack-mod.so", RTLD_LAZY);
+  if (h == NULL)
+    {
+      printf ("cannot load: %s\n", dlerror ());
+      return 1;
+    }
+
+  f = dlsym (h, "tryme");
+  if (f == NULL)
+    {
+      printf ("symbol not found: %s\n", dlerror ());
+      return 1;
+    }
+
+  /* Test if that really made our stack executable.
+     The `tryme' function should crash if not.  */
+
+  (*((void (*) (void)) f)) ();
+
+  print_maps ();
+
+  /* Test that growing the stack region gets new executable pages too.  */
+  deeper ((void (*) (void)) f);
+
+  print_maps ();
+
+#if USE_PTHREADS
+  /* Test that a fresh thread now gets an executable stack.  */
+  {
+    pthread_t th;
+    int rc = pthread_create (&th, NULL, &tryme_thread, f);
+    if (rc)
+      error (1, rc, "pthread_create");
+  }
+
+  puts ("threads go");
+  /* The existing threads' stacks should have been changed.
+     Let them run to test it.  */
+  pthread_barrier_wait (&go_barrier);
+
+  pthread_exit (0);
+#endif
+
+  return 0;
+}
+
+static void
+deeper (void (*f) (void))
+{
+  char stack[1100 * 1024];
+  memfrob (stack, sizeof stack);
+  (*f) ();
+  memfrob (stack, sizeof stack);
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"