GNU bug report logs - #11398
24.0.95; Segfault in unexec on Linux 3.3* with grsecurity/PaX

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From: Ulrich Mueller <ulm <at> gentoo.org>
To: 11398 <at> debbugs.gnu.org
Subject: bug#11398: 24.0.95; Segfault in unexec on Linux 3.3* with grsecurity/PaX
Date: Sun, 27 May 2012 14:18:30 +0200

The patch included below (against trunk of today) fixes the problem
for me.

I've not added a configure option to control usage of paxctl, because:
- Generally, the paxctl utility should be available on PaX enabled
  Linux systems.
- On non-PaX systems (but where paxctl exists for some reason) it is
  harmless if the PaX flags of temacs are modified. In any case, the
  flags of the final emacs binary will be restored to their default.


--- emacs-orig/ChangeLog
+++ emacs/ChangeLog
@@ -1,3 +1,7 @@
+2012-05-27  Ulrich Müller  <ulm <at> gentoo.org>
+
+	* configure.in (PAXCTL): Check for paxctl. (Bug#11398)
+
 2012-05-27  Paul Eggert  <eggert <at> cs.ucla.edu>
 
 	Assume gnulib does largefile.
--- emacs-orig/configure.in
+++ emacs/configure.in
@@ -713,6 +713,8 @@
 AC_PATH_PROG(INSTALL_INFO, install-info,:, /sbin)
 dnl Don't use GZIP, which is used by gzip for additional parameters.
 AC_PATH_PROG(GZIP_PROG, gzip)
+AC_PATH_PROG(PAXCTL, paxctl,,
+  [$PATH$PATH_SEPARATOR/sbin$PATH_SEPARATOR/usr/sbin])
 
 
 ## Need makeinfo >= 4.7 (?) to build the manuals.
--- emacs-orig/src/ChangeLog
+++ emacs/src/ChangeLog
@@ -1,3 +1,11 @@
+2012-05-27  Ulrich Müller  <ulm <at> gentoo.org>
+
+	* Makefile.in (PAXCTL): Define.
+	(temacs$(EXEEXT)): Disable memory randomization for the temacs
+	binary via PaX flags if the paxctl utility is available.
+	(emacs$(EXEEXT), bootstrap-emacs$(EXEEXT)): Restore PaX flags to
+	their default. (Bug#11398)
+
 2012-05-27  Paul Eggert  <eggert <at> cs.ucla.edu>
 
 	* lisp.h [REL_ALLOC]: Omit duplicate prototypes.
--- emacs-orig/src/Makefile.in
+++ emacs/src/Makefile.in
@@ -113,6 +113,12 @@
 ## $LDFLAGS or empty if NS_IMPL_GNUSTEP (for some reason).
 TEMACS_LDFLAGS2 = @TEMACS_LDFLAGS2@
 
+## If available, the full path to the paxctl program.
+## On grsecurity/PaX systems, unexec will fail due to a gap between
+## the bss section and the heap.  This can be prevented by disabling
+## memory randomization in temacs with "paxctl -r".  See bug#11398.
+PAXCTL = @PAXCTL@
+
 ## Some systems define this to request special libraries.
 LIBS_SYSTEM=@LIBS_SYSTEM@
 
@@ -403,6 +409,7 @@
 	    -f list-load-path-shadows || true; \
 	else \
 	  LC_ALL=C $(RUN_TEMACS) -batch -l loadup dump || exit 1; \
+	  test "X$(PAXCTL)" = X || $(PAXCTL) -zex emacs$(EXEEXT); \
 	  ln -f emacs$(EXEEXT) bootstrap-emacs$(EXEEXT); \
 	  ./emacs -batch -f list-load-path-shadows || true; \
 	fi
@@ -450,6 +457,8 @@
 temacs$(EXEEXT): $(START_FILES) stamp-oldxmenu $(obj) $(otherobj) $(lib)/libgnu.a
 	$(CC) $(LD_FIRSTFLAG) $(ALL_CFLAGS) $(TEMACS_LDFLAGS) $(TEMACS_LDFLAGS2) \
 	  -o temacs $(START_FILES) $(obj) $(otherobj) $(lib)/libgnu.a $(LIBES)
+	test "$(CANNOT_DUMP)" = "yes" || \
+	  test "X$(PAXCTL)" = X || $(PAXCTL) -r temacs$(EXEEXT)
 
 ## The following oldxmenu-related rules are only (possibly) used if
 ## HAVE_X11 && !USE_GTK, but there is no harm in always defining them
@@ -597,6 +606,7 @@
 	  ln -f temacs$(EXEEXT) bootstrap-emacs$(EXEEXT); \
 	else \
 	  $(RUN_TEMACS) --batch --load loadup bootstrap || exit 1; \
+	  test "X$(PAXCTL)" = X || $(PAXCTL) -zex emacs$(EXEEXT); \
 	  mv -f emacs$(EXEEXT) bootstrap-emacs$(EXEEXT); \
 	fi
 	@: Compile some files earlier to speed up further compilation.

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