diff mbox series

[4/4] elf: Restore support for _r_debug copy relocations

Message ID 3476c853788916a9a189ca0a9d31234cc05bb27d.1640284721.git.fweimer@redhat.com
State New
Headers show
Series _r_debug copy relocation support | expand

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent

Commit Message

Florian Weimer Dec. 23, 2021, 6:43 p.m. UTC
The changes in commit a93d9e03a31ec14405cb3a09aa95413b67067380
("Extend struct r_debug to support multiple namespaces [BZ #15971]")
break the dyninst dynamic instrumentation tool.

It turns out it is rather hard to use the proposed handshake
for accessing _r_debug via DT_DEBUG.  Therefore, this commit restores
copy relocation support by adjusting the copy of _r_debug in the
main executable if a copy relocation is in play.
---
 elf/Makefile               |  8 +++++++
 elf/dl-debug.c             | 46 +++++++++++++++++++++++++++++++++++---
 elf/rtld.c                 |  4 ++++
 elf/tst-dlmopen4-nonpic.c  |  2 ++
 elf/tst-dlmopen4-pic.c     |  2 ++
 elf/tst-dlmopen4.c         | 22 ++++++++++++++++++
 sysdeps/generic/ldsodefs.h |  4 ++++
 7 files changed, 85 insertions(+), 3 deletions(-)
 create mode 100644 elf/tst-dlmopen4-nonpic.c
 create mode 100644 elf/tst-dlmopen4-pic.c
diff mbox series

Patch

diff --git a/elf/Makefile b/elf/Makefile
index fe42caeb0e..000f9311ca 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -210,6 +210,7 @@  tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-align tst-align2 tst-align3 \
 	 tst-dlmodcount tst-dlopenrpath tst-deep1 \
 	 tst-dlmopen1 tst-dlmopen3 tst-dlmopen4 \
+	 tst-dlmopen4-pic tst-dlmopen4-nonpic \
 	 unload3 unload4 unload5 unload6 unload7 unload8 tst-global1 order2 \
 	 tst-audit1 tst-audit2 tst-audit8 tst-audit9 \
 	 tst-addr1 tst-thrlock \
@@ -1308,6 +1309,13 @@  $(objpfx)tst-dlmopen3.out: $(objpfx)tst-dlmopen1mod.so
 
 $(objpfx)tst-dlmopen4.out: $(objpfx)tst-dlmopen1mod.so
 
+CFLAGS-tst-dlmopen4-pic.c += -fPIC
+$(objpfx)tst-dlmopen4-pic.out: $(objpfx)tst-dlmopen1mod.so
+
+CFLAGS-tst-dlmopen4-nonpic.c += -fno-pie
+tst-dlmopen4-nonpic-no-pie = yes
+$(objpfx)tst-dlmopen4-nonpic.out: $(objpfx)tst-dlmopen1mod.so
+
 $(objpfx)tst-audit1.out: $(objpfx)tst-auditmod1.so
 tst-audit1-ENV = LD_AUDIT=$(objpfx)tst-auditmod1.so
 
diff --git a/elf/dl-debug.c b/elf/dl-debug.c
index f840a1b922..1aa79bc9b5 100644
--- a/elf/dl-debug.c
+++ b/elf/dl-debug.c
@@ -37,6 +37,32 @@  extern const int verify_link_map_members[(VERIFY_MEMBER (l_addr)
    to LM_ID_BASE + 1.  See elf/dl-debug-symbols.S.  */
 struct r_debug_extended _r_debug_array[DL_NNS - 1];
 
+/* If not null, pointer to the _r_debug in the main executable.  */
+static struct r_debug *_r_debug_main;
+
+void
+_dl_debug_post_relocate (struct link_map *main_map)
+{
+  const ElfW(Sym) *sym = _dl_lookup_direct (main_map, "_r_debug", 0x5475103c,
+					    NULL, 0);
+  if (sym != NULL && sym->st_size >= sizeof (struct r_debug))
+    {
+      struct r_debug *main_r_debug = DL_SYMBOL_ADDRESS (main_map, sym);
+      if (main_r_debug != &_r_debug_extended.base)
+	{
+	  /* The extended version of the struct is not available in
+	     the main executable because a copy relocation has been
+	     used.  r_map etc. have already been copied as part of the
+	     copy relocation processing.  */
+	  main_r_debug->r_version = 1;
+
+          /* Record that dual updates of the initial link map are
+             required.  */
+          _r_debug_main = main_r_debug;
+	}
+    }
+}
+
 /* Return the r_debug object for the namespace NS.  */
 static inline struct r_debug_extended *
 get_rdebug (Lmid_t ns)
@@ -71,6 +97,11 @@  void
 _dl_debug_change_state (struct r_debug *r, int state)
 {
   atomic_store_release (&r->r_state, state);
+#ifdef SHARED
+  if (r == &_r_debug_extended.base && _r_debug_main != NULL)
+    /* Update the copy-relocation of _r_debug.  */
+    atomic_store_release (&_r_debug_main->r_state, state);
+#endif
   _dl_debug_state ();
 }
 
@@ -103,7 +134,9 @@  _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
 	  if (ns - 1 == LM_ID_BASE)
 	    {
 	      atomic_store_release (&_r_debug_extended.r_next, r);
-	      /* Now there are multiple namespaces.  */
+	      /* Now there are multiple namespaces.  Note that this
+		 deliberately does not update the copy in the main
+		 executable (if it exists).  */
 	      atomic_store_release (&_r_debug_extended.base.r_version, 2);
 	    }
 	  else
@@ -116,8 +149,15 @@  _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
     }
 
   if (r->base.r_map == NULL)
-    atomic_store_release (&r->base.r_map,
-			  (void *) GL(dl_ns)[ns]._ns_loaded);
+    {
+      struct link_map *l = (void *) GL(dl_ns)[ns]._ns_loaded;
+      atomic_store_release (&r->base.r_map, l);
+#ifdef SHARED
+      if (ns == LM_ID_BASE && _r_debug_main != NULL)
+	/* Update the copy-relocation of _r_debug.  */
+	atomic_store_release (&_r_debug_main->r_map, l);
+#endif
+    }
 
   return &r->base;
 }
diff --git a/elf/rtld.c b/elf/rtld.c
index dd4173c2ca..ae3514eade 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -2428,6 +2428,7 @@  dl_main (const ElfW(Phdr) *phdr,
 	  if (l->l_tls_blocksize != 0 && tls_init_tp_called)
 	    _dl_add_to_slotinfo (l, true);
 	}
+
       rtld_timer_stop (&relocate_time, start);
 
       /* Now enable profiling if needed.  Like the previous call,
@@ -2439,6 +2440,9 @@  dl_main (const ElfW(Phdr) *phdr,
 	_dl_start_profile ();
     }
 
+  /* Update _r_debug if necessary.  */
+  _dl_debug_post_relocate (main_map);
+
   if ((!was_tls_init_tp_called && GL(dl_tls_max_dtv_idx) > 0)
       || count_modids != _dl_count_modids ())
     ++GL(dl_tls_generation);
diff --git a/elf/tst-dlmopen4-nonpic.c b/elf/tst-dlmopen4-nonpic.c
new file mode 100644
index 0000000000..ad4e409953
--- /dev/null
+++ b/elf/tst-dlmopen4-nonpic.c
@@ -0,0 +1,2 @@ 
+#define BUILD_FOR_NONPIC
+#include "tst-dlmopen4.c"
diff --git a/elf/tst-dlmopen4-pic.c b/elf/tst-dlmopen4-pic.c
new file mode 100644
index 0000000000..919fa85c25
--- /dev/null
+++ b/elf/tst-dlmopen4-pic.c
@@ -0,0 +1,2 @@ 
+#define BUILD_FOR_PIC
+#include "tst-dlmopen4.c"
diff --git a/elf/tst-dlmopen4.c b/elf/tst-dlmopen4.c
index 3fe150e50b..633addf419 100644
--- a/elf/tst-dlmopen4.c
+++ b/elf/tst-dlmopen4.c
@@ -53,6 +53,15 @@  do_test (void)
   TEST_COMPARE (debug->base.r_version, 1);
   TEST_VERIFY_EXIT (debug->r_next == NULL);
 
+#ifdef BUILD_FOR_PIC
+  /* In a PIC build, using _r_debug directly should give us the same
+     object.  */
+  TEST_VERIFY (&_r_debug == &debug->base);
+#endif
+#ifdef BUILD_FOR_NONPIC
+  TEST_COMPARE (_r_debug.r_version, 1);
+#endif
+
   void *h = xdlmopen (LM_ID_NEWLM, "$ORIGIN/tst-dlmopen1mod.so",
 		      RTLD_LAZY);
 
@@ -64,6 +73,19 @@  do_test (void)
   const char *name = basename (debug->r_next->base.r_map->l_name);
   TEST_COMPARE_STRING (name, "tst-dlmopen1mod.so");
 
+#ifdef BUILD_FOR_NONPIC
+  /* If a copy relocation is used, it must be at version 1.  */
+  if (&_r_debug != &debug->base)
+    {
+      TEST_COMPARE (_r_debug.r_version, 1);
+      TEST_COMPARE ((uintptr_t) _r_debug.r_map,
+		    (uintptr_t) debug->base.r_map);
+      TEST_COMPARE (_r_debug.r_brk, debug->base.r_brk);
+      TEST_COMPARE (_r_debug.r_state, debug->base.r_state);
+      TEST_COMPARE (_r_debug.r_ldbase, debug->base.r_ldbase);
+    }
+#endif
+
   xdlclose (h);
 
   return 0;
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 8ff06d6b02..4658636d71 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -1137,6 +1137,10 @@  rtld_hidden_proto (_dl_debug_state)
 extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
      attribute_hidden;
 
+/* This is called after relocation processing to handle a potential
+   copy relocation for _r_debug.  */
+void _dl_debug_post_relocate (struct link_map *main_map) attribute_hidden;
+
 /* Update the `r_map' member and return the address of `struct r_debug'
    of the namespace NS.  */
 extern struct r_debug *_dl_debug_update (Lmid_t ns) attribute_hidden;