elf: Rework exception handling in the dynamic loader [BZ #25486]

The old exception handling implementation used function interposition
to replace the dynamic loader implementation (no TLS support) with the
libc implementation (TLS support).  This results in problems if the
link order between the dynamic loader and libc is reversed (bug 25486).

The new implementation moves the entire implementation of the
exception handling functions back into the dynamic loader, using
THREAD_GETMEM and THREAD_SETMEM for thread-local data support.
These depends on Hurd support for these macros, added in commit
b65a82e4e757c1e6cb7073916 ("hurd: Add THREAD_GET/SETMEM/_NC").

One small obstacle is that the exception handling facilities are used
before the TCB has been set up, so a check is needed if the TCB is
available.  If not, a regular global variable is used to store the
exception handling information.

Also rename dl-error.c to dl-catch.c, to avoid confusion with the
dlerror function.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

6 files changed, 79 insertions, 138 deletions

diff --git a/elf/Makefile b/elf/Makefile
index 5f7d222..eca7b28 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -34,7 +34,6 @@ routines = \
   dl-addr \
   dl-addr-obj \
   dl-early_allocate \
-  dl-error \
   dl-iteratephdr \
   dl-libc \
   dl-origin \
@@ -54,6 +53,7 @@ routines = \
 dl-routines = \
   dl-call-libc-early-init \
   dl-call_fini \
+  dl-catch \
   dl-close \
   dl-debug \
   dl-debug-symbols \
@@ -134,7 +134,6 @@ rtld-routines = \
   dl-diagnostics-cpu \
   dl-diagnostics-kernel \
   dl-environ \
-  dl-error-minimal \
   dl-hwcaps \
   dl-hwcaps-subdirs \
   dl-hwcaps_split \
diff --git a/elf/Versions b/elf/Versions
index a9ff278..4614ace 100644
--- a/elf/Versions
+++ b/elf/Versions
@@ -31,10 +31,6 @@ libc {
   GLIBC_PRIVATE {
     # functions used in other libraries
     __libc_early_init;
-
-    # Internal error handling support.  Interposes the functions in ld.so.
-    _dl_signal_exception; _dl_catch_exception;
-    _dl_signal_error; _dl_catch_error;
   }
 }
 
@@ -77,10 +73,8 @@ ld {
 
     # Internal error handling support.
     _dl_exception_create; _dl_exception_create_format; _dl_exception_free;
-
-    # Internal error handling support.  Interposed by libc.so.
     _dl_signal_exception; _dl_catch_exception;
-    _dl_signal_error; _dl_catch_error;
+    _dl_signal_error;
 
     # Set value of a tunable.
     __tunable_get_val;
diff --git a/elf/dl-error-skeleton.c b/elf/dl-catch.c
index 8abf437..54763dd 100644
--- a/elf/dl-error-skeleton.c
+++ b/elf/dl-catch.c
@@ -1,4 +1,4 @@
-/* Template for error handling for runtime dynamic linker.
+/* Exception handling in the dynamic linker.
    Copyright (C) 1995-2022 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
@@ -16,16 +16,6 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-/* The following macro needs to be defined before including this
-   skeleton file:
-
-   DL_ERROR_BOOTSTRAP
-
-     If 1, do not use TLS and implement _dl_signal_cerror and
-     _dl_receive_error.  If 0, TLS is used, and the variants with
-     error callbacks are not provided.  */
-
-
 #include <libintl.h>
 #include <setjmp.h>
 #include <stdbool.h>
@@ -34,39 +24,54 @@
 #include <unistd.h>
 #include <ldsodefs.h>
 #include <stdio.h>
+#include <tls.h>
 
 /* This structure communicates state between _dl_catch_error and
    _dl_signal_error.  */
-struct catch
+struct rtld_catch
   {
     struct dl_exception *exception; /* The exception data is stored there.  */
     volatile int *errcode;	/* Return value of _dl_signal_error.  */
     jmp_buf env;		/* longjmp here on error.  */
   };
 
-/* Multiple threads at once can use the `_dl_catch_error' function.  The
-   calls can come from `_dl_map_object_deps', `_dlerror_run', or from
-   any of the libc functionality which loads dynamic objects (NSS, iconv).
-   Therefore we have to be prepared to save the state in thread-local
-   memory.  */
-#if !DL_ERROR_BOOTSTRAP
-static __thread struct catch *catch_hook attribute_tls_model_ie;
-#else
-/* The version of this code in ld.so cannot use thread-local variables
-   and is used during bootstrap only.  */
-static struct catch *catch_hook;
+/* Multiple threads at once can use the `_dl_catch_error' function.
+   The calls can come from `_dl_map_object_deps', `_dlerror_run', or
+   from any of the libc functionality which loads dynamic objects
+   (NSS, iconv).  Therefore we have to be prepared to save the state
+   in thread-local memory.  We use THREAD_GETMEM and THREAD_SETMEM
+   instead of ELF TLS because ELF TLS is not available in the dynamic
+   loader.  Additionally, the exception handling mechanism must be
+   usable before the TCB has been set up, which is why
+   rtld_catch_notls is used if !__rtld_tls_init_tp_called.  This is
+   not needed for static builds, where initialization completes before
+   static dlopen etc. can be called.  */
+
+#if IS_IN (rtld)
+static struct rtld_catch *rtld_catch_notls;
 #endif
 
-#if DL_ERROR_BOOTSTRAP
-/* This points to a function which is called when an continuable error is
-   received.  Unlike the handling of `catch' this function may return.
-   The arguments will be the `errstring' and `objname'.
+static struct rtld_catch *
+get_catch (void)
+{
+#if IS_IN (rtld)
+  if (!__rtld_tls_init_tp_called)
+    return rtld_catch_notls;
+  else
+#endif
+    return THREAD_GETMEM (THREAD_SELF, rtld_catch);
+}
 
-   Since this functionality is not used in normal programs (only in ld.so)
-   we do not care about multi-threaded programs here.  We keep this as a
-   global variable.  */
-static receiver_fct receiver;
-#endif /* DL_ERROR_BOOTSTRAP */
+static void
+set_catch (struct rtld_catch *catch)
+{
+#if IS_IN (rtld)
+  if (!__rtld_tls_init_tp_called)
+    rtld_catch_notls = catch;
+  else
+#endif
+    THREAD_SETMEM (THREAD_SELF, rtld_catch, catch);
+}
 
 /* Lossage while resolving the program's own symbols is always fatal.  */
 static void
@@ -89,7 +94,7 @@ void
 _dl_signal_exception (int errcode, struct dl_exception *exception,
 		      const char *occasion)
 {
-  struct catch *lcatch = catch_hook;
+  struct rtld_catch *lcatch = get_catch ();
   if (lcatch != NULL)
     {
       *lcatch->exception = *exception;
@@ -101,13 +106,13 @@ _dl_signal_exception (int errcode, struct dl_exception *exception,
   else
     fatal_error (errcode, exception->objname, occasion, exception->errstring);
 }
-libc_hidden_def (_dl_signal_exception)
+rtld_hidden_def (_dl_signal_exception)
 
 void
 _dl_signal_error (int errcode, const char *objname, const char *occation,
 		  const char *errstring)
 {
-  struct catch *lcatch = catch_hook;
+  struct rtld_catch *lcatch = get_catch ();
 
   if (! errstring)
     errstring = N_("DYNAMIC LINKER BUG!!!");
@@ -123,10 +128,18 @@ _dl_signal_error (int errcode, const char *objname, const char *occation,
   else
     fatal_error (errcode, objname, occation, errstring);
 }
-libc_hidden_def (_dl_signal_error)
+rtld_hidden_def (_dl_signal_error)
+
+#if IS_IN (rtld)
+/* This points to a function which is called when a continuable error is
+   received.  Unlike the handling of `catch' this function may return.
+   The arguments will be the `errstring' and `objname'.
 
+   Since this functionality is not used in normal programs (only in ld.so)
+   we do not care about multi-threaded programs here.  We keep this as a
+   global variable.  */
+static receiver_fct receiver;
 
-#if DL_ERROR_BOOTSTRAP
 void
 _dl_signal_cexception (int errcode, struct dl_exception *exception,
 		       const char *occasion)
@@ -167,7 +180,23 @@ _dl_signal_cerror (int errcode, const char *objname, const char *occation,
   else
     _dl_signal_error (errcode, objname, occation, errstring);
 }
-#endif /* DL_ERROR_BOOTSTRAP */
+
+void
+_dl_receive_error (receiver_fct fct, void (*operate) (void *), void *args)
+{
+  struct rtld_catch *old_catch = get_catch ();
+  receiver_fct old_receiver = receiver;
+
+  /* Set the new values.  */
+  set_catch (NULL);
+  receiver = fct;
+
+  (*operate) (args);
+
+  set_catch (old_catch);
+  receiver = old_receiver;
+}
+#endif
 
 int
 _dl_catch_exception (struct dl_exception *exception,
@@ -177,11 +206,11 @@ _dl_catch_exception (struct dl_exception *exception,
      Exceptions during operate (args) are fatal.  */
   if (exception == NULL)
     {
-      struct catch *const old = catch_hook;
-      catch_hook = NULL;
+      struct rtld_catch *old_catch = get_catch ();
+      set_catch (NULL);
       operate (args);
       /* If we get here, the operation was successful.  */
-      catch_hook = old;
+      set_catch (old_catch);
       return 0;
     }
 
@@ -194,19 +223,19 @@ _dl_catch_exception (struct dl_exception *exception,
      in _dl_signal_error (before longjmp).  */
   volatile int errcode;
 
-  struct catch c;
+  struct rtld_catch c;
   /* Don't use an initializer since we don't need to clear C.env.  */
   c.exception = exception;
   c.errcode = &errcode;
 
-  struct catch *const old = catch_hook;
-  catch_hook = &c;
+  struct rtld_catch *old = get_catch ();
+  set_catch (&c);
 
   /* Do not save the signal mask.  */
   if (__builtin_expect (__sigsetjmp (c.env, 0), 0) == 0)
     {
       (*operate) (args);
-      catch_hook = old;
+      set_catch (old);
       *exception = (struct dl_exception) { NULL };
       return 0;
     }
@@ -214,10 +243,10 @@ _dl_catch_exception (struct dl_exception *exception,
   /* We get here only if we longjmp'd out of OPERATE.
      _dl_signal_exception has already stored values into
      *EXCEPTION.  */
-  catch_hook = old;
+  set_catch (old);
   return errcode;
 }
-libc_hidden_def (_dl_catch_exception)
+rtld_hidden_def (_dl_catch_exception)
 
 int
 _dl_catch_error (const char **objname, const char **errstring,
@@ -230,34 +259,3 @@ _dl_catch_error (const char **objname, const char **errstring,
   *mallocedp = exception.message_buffer == exception.errstring;
   return errorcode;
 }
-libc_hidden_def (_dl_catch_error)
-
-#if DL_ERROR_BOOTSTRAP
-void
-_dl_receive_error (receiver_fct fct, void (*operate) (void *), void *args)
-{
-  struct catch *old_catch = catch_hook;
-  receiver_fct old_receiver = receiver;
-
-  /* Set the new values.  */
-  catch_hook = NULL;
-  receiver = fct;
-
-  (*operate) (args);
-
-  catch_hook = old_catch;
-  receiver = old_receiver;
-}
-
-/* Forwarder used for initializing GLRO (_dl_catch_error).  */
-int
-_rtld_catch_error (const char **objname, const char **errstring,
-		   bool *mallocedp, void (*operate) (void *),
-		   void *args)
-{
-  /* The reference to _dl_catch_error will eventually be relocated to
-     point to the implementation in libc.so.  */
-  return _dl_catch_error (objname, errstring, mallocedp, operate, args);
-}
-
-#endif /* DL_ERROR_BOOTSTRAP */
diff --git a/elf/dl-error-minimal.c b/elf/dl-error-minimal.c
deleted file mode 100644
index 9b833b9..0000000
--- a/elf/dl-error-minimal.c
+++ /dev/null
@@ -1,23 +0,0 @@
-/* Error handling for runtime dynamic linker, minimal version.
-   Copyright (C) 1995-2022 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <https://www.gnu.org/licenses/>.  */
-
-/* This version does lives in ld.so, does not use thread-local data
-   and supports _dl_signal_cerror and _dl_receive_error.  */
-
-#define DL_ERROR_BOOTSTRAP 1
-#include "dl-error-skeleton.c"
diff --git a/elf/dl-error.c b/elf/dl-error.c
deleted file mode 100644
index 0b7332a..0000000
--- a/elf/dl-error.c
+++ /dev/null
@@ -1,27 +0,0 @@
-/* Error handling for runtime dynamic linker, full version.
-   Copyright (C) 1995-2022 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <https://www.gnu.org/licenses/>.  */
-
-/* This implementation lives in libc.so because it uses thread-local
-   data, which is not available in ld.so.  It interposes the version
-   in dl-error-minimal.c after ld.so bootstrap.
-
-   The signal/catch mechanism is used by the audit framework, which
-   means that even in ld.so, not all errors are fatal.  */
-
-#define DL_ERROR_BOOTSTRAP 0
-#include "dl-error-skeleton.c"
diff --git a/elf/rtld.c b/elf/rtld.c
index 221be5c..8671594 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -370,7 +370,7 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
     ._dl_lookup_symbol_x = _dl_lookup_symbol_x,
     ._dl_open = _dl_open,
     ._dl_close = _dl_close,
-    ._dl_catch_error = _rtld_catch_error,
+    ._dl_catch_error = _dl_catch_error,
     ._dl_error_free = _dl_error_free,
     ._dl_tls_get_addr_soft = _dl_tls_get_addr_soft,
     ._dl_libc_freeres = __rtld_libc_freeres,