[PATCH] W^X Java closure fixes

Jakub Jelinek jakub@redhat.com
Thu Mar 29 23:35:00 GMT 2007


Hi!

libjava now (thanks to Alex) uses ffi_closure_{alloc,free} to allocate
trampolines separately.  But boehm-gc's default hasn't been changed, which
means all GC memory is still executable (where allowed) or just will fail
to mmap (if e.g. SELinux policy disallows PROT_WRITE|PROT_EXEC mappings).
The following patch changes that, by setting NO_EXECUTE_PERMISSION always
to 1 in gcc's boehm-gc (not sure what should boehm-gc's upstream do here,
it can't be so sure nobody uses GC memory for code).
Additionally, the patch has a quick check for SELinux presence on Linux
and will skip the PROT_READ|PROT_WRITE|PROT_EXEC mmap if it is (while try it
if SELinux is not present or on other OSes), because such mmap would trigger
annoying audit messages.

Ok for trunk?

2007-03-29  Jakub Jelinek  <jakub@redhat.com>

	* src/closures.c: Include sys/statfs.h.
	(_GNU_SOURCE): Define on Linux.
	(FFI_MMAP_EXEC_SELINUX): Define.
	(selinux_enabled): New variable.
	(selinux_enabled_check): New function.
	(is_selinux_enabled): Define.
	(dlmmap): Use it.

	* configure.ac (NO_EXECUTE_PERMISSION): Set by default.
	* configure: Rebuilt.

--- libffi/src/closures.c.jj	2007-03-27 15:57:33.000000000 +0200
+++ libffi/src/closures.c	2007-03-27 16:29:34.000000000 +0200
@@ -23,6 +23,10 @@
    OTHER DEALINGS IN THE SOFTWARE.
    ----------------------------------------------------------------------- */
 
+#if defined __linux__ && !defined _GNU_SOURCE
+#define _GNU_SOURCE 1
+#endif
+
 #include <ffi.h>
 #include <ffi_common.h>
 
@@ -39,6 +43,15 @@
 # endif
 #endif
 
+#if FFI_MMAP_EXEC_WRIT && !defined FFI_MMAP_EXEC_SELINUX
+# ifdef __linux__
+/* When defined to 1 check for SELinux and if SELinux is active,
+   don't attempt PROT_EXEC|PROT_WRITE mapping at all, as that
+   might cause audit messages.  */
+#  define FFI_MMAP_EXEC_SELINUX 1
+# endif
+#endif
+
 #if FFI_CLOSURES
 
 # if FFI_MMAP_EXEC_WRIT
@@ -87,6 +100,55 @@
 #include <sys/mman.h>
 #define LACKS_SYS_MMAN_H 1
 
+#if FFI_MMAP_EXEC_SELINUX
+#include <sys/statfs.h>
+#include <stdlib.h>
+
+static int selinux_enabled = -1;
+
+static int
+selinux_enabled_check (void)
+{
+  struct statfs sfs;
+  FILE *f;
+  char *buf = NULL;
+  size_t len = 0;
+
+  if (statfs ("/selinux", &sfs) >= 0
+      && (unsigned int) sfs.f_type == 0xf97cff8cU)
+    return 1;
+  f = fopen ("/proc/mounts", "r");
+  if (f == NULL)
+    return 0;
+  while (getline (&buf, &len, f) >= 0)
+    {
+      char *p = strchr (buf, ' ');
+      if (p == NULL)
+        break;
+      p = strchr (p + 1, ' ');
+      if (p == NULL)
+        break;
+      if (strncmp (p + 1, "selinuxfs ", 10) != 0)
+        {
+          free (buf);
+          fclose (f);
+          return 1;
+        }
+    }
+  free (buf);
+  fclose (f);
+  return 0;
+}
+
+#define is_selinux_enabled() (selinux_enabled >= 0 ? selinux_enabled \
+			      : (selinux_enabled = selinux_enabled_check ()))
+
+#else
+
+#define is_selinux_enabled() 0
+
+#endif
+
 #define MAYBE_UNUSED __attribute__((__unused__))
 
 /* Declare all functions defined in dlmalloc.c as static.  */
@@ -358,7 +420,7 @@ dlmmap (void *start, size_t length, int 
   printf ("mapping in %zi\n", length);
 #endif
 
-  if (execfd == -1)
+  if (execfd == -1 && !is_selinux_enabled ())
     {
       ptr = mmap (start, length, prot | PROT_EXEC, flags, fd, offset);
 
--- boehm-gc/configure.ac.jj	2007-02-20 22:39:56.000000000 +0100
+++ boehm-gc/configure.ac	2007-03-29 12:30:30.000000000 +0200
@@ -338,11 +338,9 @@ LIBS="$oldLIBS"
 
 # Configuration of machine-dependent code
 #
-# We don't set NO_EXECUTE_PERMISSION by default because gcj (and
-# anything else that creates trampolines in gc-allocated memory)
-# always needs exec permission.  The exceptions to this are IA-64 and
-# some variations of Power PC, where trampolines don't contain
-# executable code.
+# Set NO_EXECUTE_PERMISSION by default because gcj already uses
+# ffi_closure_{alloc,free} which takes care of allocating trampolines
+# in executable memory.
 #
 AC_MSG_CHECKING(which machine-dependent code should be used)
 machdep=
@@ -385,10 +383,10 @@ case "$host" in
     machdep="sparc_mach_dep.lo"
     ;;
  ia64-*-*)
-    AC_DEFINE(NO_EXECUTE_PERMISSION,1,[cause some or all of the heap to not have execute permission])
     machdep="mach_dep.lo ia64_save_regs_in_stack.lo"
     ;;
 esac
+AC_DEFINE(NO_EXECUTE_PERMISSION,1,[cause some or all of the heap to not have execute permission])
 if test x"$machdep" = x; then
 AC_MSG_RESULT($machdep)
    machdep="mach_dep.lo"
--- boehm-gc/configure.jj	2007-02-20 22:39:56.000000000 +0100
+++ boehm-gc/configure	2007-03-29 12:31:25.000000000 +0200
@@ -6560,11 +6560,9 @@ LIBS="$oldLIBS"
 
 # Configuration of machine-dependent code
 #
-# We don't set NO_EXECUTE_PERMISSION by default because gcj (and
-# anything else that creates trampolines in gc-allocated memory)
-# always needs exec permission.  The exceptions to this are IA-64 and
-# some variations of Power PC, where trampolines don't contain
-# executable code.
+# Set NO_EXECUTE_PERMISSION by default because gcj already uses
+# ffi_closure_{alloc,free} which takes care of allocating trampolines
+# in executable memory.
 #
 echo "$as_me:$LINENO: checking which machine-dependent code should be used" >&5
 echo $ECHO_N "checking which machine-dependent code should be used... $ECHO_C" >&6
@@ -6625,14 +6623,14 @@ _ACEOF
     machdep="sparc_mach_dep.lo"
     ;;
  ia64-*-*)
+    machdep="mach_dep.lo ia64_save_regs_in_stack.lo"
+    ;;
+esac
 
 cat >>confdefs.h <<\_ACEOF
 #define NO_EXECUTE_PERMISSION 1
 _ACEOF
 
-    machdep="mach_dep.lo ia64_save_regs_in_stack.lo"
-    ;;
-esac
 if test x"$machdep" = x; then
 echo "$as_me:$LINENO: result: $machdep" >&5
 echo "${ECHO_T}$machdep" >&6

	Jakub



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