Fix _dl_profile_fixup data-dependency issue (Bug 23690)

There is a data-dependency between the fields of struct l_reloc_result
and the field used as the initialization guard. Users of the guard
expect writes to the structure to be observable when they also observe
the guard initialized. The solution for this problem is to use an acquire
and release load and store to ensure previous writes to the structure are
observable if the guard is initialized.

The previous implementation used DL_FIXUP_VALUE_ADDR (l_reloc_result->addr)
as the initialization guard, making it impossible for some architectures
to load and store it atomically, i.e. hppa and ia64, due to its larger size.

This commit adds an unsigned int to l_reloc_result to be used as the new
initialization guard of the struct, making it possible to load and store
it atomically in all architectures. The fix ensures that the values
observed in l_reloc_result are consistent and do not lead to crashes.
The algorithm is documented in the code in elf/dl-runtime.c
(_dl_profile_fixup). Not all data races have been eliminated.

Tested with build-many-glibcs and on powerpc, powerpc64, and powerpc64le.

	[BZ #23690]
	* elf/dl-runtime.c (_dl_profile_fixup): Guarantee memory
	modification order when accessing reloc_result->addr.
	* include/link.h (reloc_result): Add field init.
	* nptl/Makefile (tests): Add tst-audit-threads.
	(modules-names): Add tst-audit-threads-mod1 and
	tst-audit-threads-mod2.
	Add rules to build tst-audit-threads.
	* nptl/tst-audit-threads-mod1.c: New file.
	* nptl/tst-audit-threads-mod2.c: Likewise.
	* nptl/tst-audit-threads.c: Likewise.
	* nptl/tst-audit-threads.h: Likewise.

Signed-off-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/nptl/Makefile b/nptl/Makefile
index 982e43adfa..98b0aa01c7 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -382,7 +382,8 @@ tests += tst-cancelx2 tst-cancelx3 tst-cancelx4 tst-cancelx5 \
 	 tst-cleanupx0 tst-cleanupx1 tst-cleanupx2 tst-cleanupx3 tst-cleanupx4 \
 	 tst-oncex3 tst-oncex4
 ifeq ($(build-shared),yes)
-tests += tst-atfork2 tst-tls4 tst-_res1 tst-fini1 tst-compat-forwarder
+tests += tst-atfork2 tst-tls4 tst-_res1 tst-fini1 tst-compat-forwarder \
+	 tst-audit-threads
 tests-internal += tst-tls3 tst-tls3-malloc tst-tls5 tst-stackguard1
 tests-nolibpthread += tst-fini1
 ifeq ($(have-z-execstack),yes)
@@ -394,7 +395,8 @@ modules-names = tst-atfork2mod tst-tls3mod tst-tls4moda tst-tls4modb \
 		tst-tls5mod tst-tls5moda tst-tls5modb tst-tls5modc \
 		tst-tls5modd tst-tls5mode tst-tls5modf tst-stack4mod \
 		tst-_res1mod1 tst-_res1mod2 tst-execstack-mod tst-fini1mod \
-		tst-join7mod tst-compat-forwarder-mod
+		tst-join7mod tst-compat-forwarder-mod tst-audit-threads-mod1 \
+		tst-audit-threads-mod2
 extra-test-objs += $(addsuffix .os,$(strip $(modules-names))) \
 		   tst-cleanup4aux.o tst-cleanupx4aux.o
 test-extras += tst-cleanup4aux tst-cleanupx4aux
@@ -712,6 +714,14 @@ $(objpfx)tst-compat-forwarder: $(objpfx)tst-compat-forwarder-mod.so
 
 tst-mutex10-ENV = GLIBC_TUNABLES=glibc.elision.enable=1
 
+# Protect against a build using -Wl,-z,now.
+LDFLAGS-tst-audit-threads-mod1.so = -Wl,-z,lazy
+LDFLAGS-tst-audit-threads-mod2.so = -Wl,-z,lazy
+LDFLAGS-tst-audit-threads = -Wl,-z,lazy
+$(objpfx)tst-audit-threads: $(objpfx)tst-audit-threads-mod2.so
+$(objpfx)tst-audit-threads.out: $(objpfx)tst-audit-threads-mod1.so
+tst-audit-threads-ENV = LD_AUDIT=$(objpfx)tst-audit-threads-mod1.so
+
 # The tests here better do not run in parallel
 ifneq ($(filter %tests,$(MAKECMDGOALS)),)
 .NOTPARALLEL: