[glibc/release/2.34/master] rtld: Use generic argv adjustment in ld.so [BZ #23293]

[glibc/release/2.34/master] rtld: Use generic argv adjustment in ld.so [BZ #23293]

[Szabolcs Nagy]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c73c79af7d6f1124fbfa5d935b4f620217d6a2ec

commit c73c79af7d6f1124fbfa5d935b4f620217d6a2ec
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Fri Jun 15 16:14:58 2018 +0100

    rtld: Use generic argv adjustment in ld.so [BZ #23293]
    
    When an executable is invoked as
    
      ./ld.so [ld.so-args] ./exe [exe-args]
    
    then the argv is adujusted in ld.so before calling the entry point of
    the executable so ld.so args are not visible to it.  On most targets
    this requires moving argv, env and auxv on the stack to ensure correct
    stack alignment at the entry point.  This had several issues:
    
    - The code for this adjustment on the stack is written in asm as part
      of the target specific ld.so _start code which is hard to maintain.
    
    - The adjustment is done after _dl_start returns, where it's too late
      to update GLRO(dl_auxv), as it is already readonly, so it points to
      memory that was clobbered by the adjustment. This is bug 23293.
    
    - _environ is also wrong in ld.so after the adjustment, but it is
      likely not used after _dl_start returns so this is not user visible.
    
    - _dl_argv was updated, but for this it was moved out of relro, which
      changes security properties across targets unnecessarily.
    
    This patch introduces a generic _dl_start_args_adjust function that
    handles the argument adjustments after ld.so processed its own args
    and before relro protection is applied.
    
    The same algorithm is used on all targets, _dl_skip_args is now 0, so
    existing target specific adjustment code is no longer used.  The bug
    affects aarch64, alpha, arc, arm, csky, ia64, nios2, s390-32 and sparc,
    other targets don't need the change in principle, only for consistency.
    
    The GNU Hurd start code relied on _dl_skip_args after dl_main returned,
    now it checks directly if args were adjusted and fixes the Hurd startup
    data accordingly.
    
    Follow up patches can remove _dl_skip_args and DL_ARGV_NOT_RELRO.
    
    Tested on aarch64-linux-gnu and cross tested on i686-gnu.
    
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
    (cherry picked from commit ad43cac44a6860eaefcadadfb2acb349921e96bf)

Diff:
---
 elf/rtld.c                    | 73 +++++++++++++++++++++++++++++++++++--------
 sysdeps/mach/hurd/dl-sysdep.c | 30 ++++++++----------
 2 files changed, 73 insertions(+), 30 deletions(-)

diff --git a/elf/rtld.c b/elf/rtld.c
index 197efe1316..c59f0f17bd 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1081,6 +1081,62 @@ load_audit_modules (struct link_map *main_map, struct audit_list *audit_list)
     }
 }
 
+/* Adjusts the contents of the stack and related globals for the user
+   entry point.  The ld.so processed skip_args arguments and bumped
+   _dl_argv and _dl_argc accordingly.  Those arguments are removed from
+   argv here.  */
+static void
+_dl_start_args_adjust (int skip_args)
+{
+  void **sp = (void **) (_dl_argv - skip_args - 1);
+  void **p = sp + skip_args;
+
+  if (skip_args == 0)
+    return;
+
+  /* Sanity check.  */
+  intptr_t argc = (intptr_t) sp[0] - skip_args;
+  assert (argc == _dl_argc);
+
+  /* Adjust argc on stack.  */
+  sp[0] = (void *) (intptr_t) _dl_argc;
+
+  /* Update globals in rtld.  */
+  _dl_argv -= skip_args;
+  _environ -= skip_args;
+
+  /* Shuffle argv down.  */
+  do
+    *++sp = *++p;
+  while (*p != NULL);
+
+  assert (_environ == (char **) (sp + 1));
+
+  /* Shuffle envp down.  */
+  do
+    *++sp = *++p;
+  while (*p != NULL);
+
+#ifdef HAVE_AUX_VECTOR
+  void **auxv = (void **) GLRO(dl_auxv) - skip_args;
+  GLRO(dl_auxv) = (ElfW(auxv_t) *) auxv; /* Aliasing violation.  */
+  assert (auxv == sp + 1);
+
+  /* Shuffle auxv down. */
+  ElfW(auxv_t) ax;
+  char *oldp = (char *) (p + 1);
+  char *newp = (char *) (sp + 1);
+  do
+    {
+      memcpy (&ax, oldp, sizeof (ax));
+      memcpy (newp, &ax, sizeof (ax));
+      oldp += sizeof (ax);
+      newp += sizeof (ax);
+    }
+  while (ax.a_type != AT_NULL);
+#endif
+}
+
 static void
 dl_main (const ElfW(Phdr) *phdr,
 	 ElfW(Word) phnum,
@@ -1137,6 +1193,7 @@ dl_main (const ElfW(Phdr) *phdr,
       rtld_is_main = true;
 
       char *argv0 = NULL;
+      char **orig_argv = _dl_argv;
 
       /* Note the place where the dynamic linker actually came from.  */
       GL(dl_rtld_map).l_name = rtld_progname;
@@ -1151,7 +1208,6 @@ dl_main (const ElfW(Phdr) *phdr,
 		GLRO(dl_lazy) = -1;
 	      }
 
-	    ++_dl_skip_args;
 	    --_dl_argc;
 	    ++_dl_argv;
 	  }
@@ -1160,14 +1216,12 @@ dl_main (const ElfW(Phdr) *phdr,
 	    if (state.mode != rtld_mode_help)
 	      state.mode = rtld_mode_verify;
 
-	    ++_dl_skip_args;
 	    --_dl_argc;
 	    ++_dl_argv;
 	  }
 	else if (! strcmp (_dl_argv[1], "--inhibit-cache"))
 	  {
 	    GLRO(dl_inhibit_cache) = 1;
-	    ++_dl_skip_args;
 	    --_dl_argc;
 	    ++_dl_argv;
 	  }
@@ -1177,7 +1231,6 @@ dl_main (const ElfW(Phdr) *phdr,
 	    state.library_path = _dl_argv[2];
 	    state.library_path_source = "--library-path";
 
-	    _dl_skip_args += 2;
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
@@ -1186,7 +1239,6 @@ dl_main (const ElfW(Phdr) *phdr,
 	  {
 	    GLRO(dl_inhibit_rpath) = _dl_argv[2];
 
-	    _dl_skip_args += 2;
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
@@ -1194,14 +1246,12 @@ dl_main (const ElfW(Phdr) *phdr,
 	  {
 	    audit_list_add_string (&state.audit_list, _dl_argv[2]);
 
-	    _dl_skip_args += 2;
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
 	else if (! strcmp (_dl_argv[1], "--preload") && _dl_argc > 2)
 	  {
 	    state.preloadarg = _dl_argv[2];
-	    _dl_skip_args += 2;
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
@@ -1209,7 +1259,6 @@ dl_main (const ElfW(Phdr) *phdr,
 	  {
 	    argv0 = _dl_argv[2];
 
-	    _dl_skip_args += 2;
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
@@ -1217,7 +1266,6 @@ dl_main (const ElfW(Phdr) *phdr,
 		 && _dl_argc > 2)
 	  {
 	    state.glibc_hwcaps_prepend = _dl_argv[2];
-	    _dl_skip_args += 2;
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
@@ -1225,7 +1273,6 @@ dl_main (const ElfW(Phdr) *phdr,
 		 && _dl_argc > 2)
 	  {
 	    state.glibc_hwcaps_mask = _dl_argv[2];
-	    _dl_skip_args += 2;
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
@@ -1234,7 +1281,6 @@ dl_main (const ElfW(Phdr) *phdr,
 	  {
 	    state.mode = rtld_mode_list_tunables;
 
-	    ++_dl_skip_args;
 	    --_dl_argc;
 	    ++_dl_argv;
 	  }
@@ -1243,7 +1289,6 @@ dl_main (const ElfW(Phdr) *phdr,
 	  {
 	    state.mode = rtld_mode_list_diagnostics;
 
-	    ++_dl_skip_args;
 	    --_dl_argc;
 	    ++_dl_argv;
 	  }
@@ -1289,7 +1334,6 @@ dl_main (const ElfW(Phdr) *phdr,
 	    _dl_usage (ld_so_name, NULL);
 	}
 
-      ++_dl_skip_args;
       --_dl_argc;
       ++_dl_argv;
 
@@ -1391,6 +1435,9 @@ dl_main (const ElfW(Phdr) *phdr,
       /* Set the argv[0] string now that we've processed the executable.  */
       if (argv0 != NULL)
         _dl_argv[0] = argv0;
+
+      /* Adjust arguments for the application entry point.  */
+      _dl_start_args_adjust (_dl_argv - orig_argv);
     }
   else
     {
diff --git a/sysdeps/mach/hurd/dl-sysdep.c b/sysdeps/mach/hurd/dl-sysdep.c
index 4b2072e5d5..5c0f8e46bf 100644
--- a/sysdeps/mach/hurd/dl-sysdep.c
+++ b/sysdeps/mach/hurd/dl-sysdep.c
@@ -106,6 +106,7 @@ _dl_sysdep_start (void **start_argptr,
 {
   void go (intptr_t *argdata)
     {
+      char *orig_argv0;
       char **p;
 
       /* Cache the information in various global variables.  */
@@ -114,6 +115,8 @@ _dl_sysdep_start (void **start_argptr,
       _environ = &_dl_argv[_dl_argc + 1];
       for (p = _environ; *p++;); /* Skip environ pointers and terminator.  */
 
+      orig_argv0 = _dl_argv[0];
+
       if ((void *) p == _dl_argv[0])
 	{
 	  static struct hurd_startup_data nodata;
@@ -204,30 +207,23 @@ unfmh();			/* XXX */
 
       /* The call above might screw a few things up.
 
-	 First of all, if _dl_skip_args is nonzero, we are ignoring
-	 the first few arguments.  However, if we have no Hurd startup
-	 data, it is the magical convention that ARGV[0] == P.  The
+	 P is the location after the terminating NULL of the list of
+	 environment variables.  It has to point to the Hurd startup
+	 data or if that's missing then P == ARGV[0] must hold. The
 	 startup code in init-first.c will get confused if this is not
 	 the case, so we must rearrange things to make it so.  We'll
-	 overwrite the origional ARGV[0] at P with ARGV[_dl_skip_args].
+	 recompute P and move the Hurd data or the new ARGV[0] there.
 
-	 Secondly, if we need to be secure, it removes some dangerous
-	 environment variables.  If we have no Hurd startup date this
-	 changes P (since that's the location after the terminating
-	 NULL in the list of environment variables).  We do the same
-	 thing as in the first case but make sure we recalculate P.
-	 If we do have Hurd startup data, we have to move the data
-	 such that it starts just after the terminating NULL in the
-	 environment list.
+	 Note: directly invoked ld.so can move arguments and env vars.
 
 	 We use memmove, since the locations might overlap.  */
-      if (__libc_enable_secure || _dl_skip_args)
-	{
-	  char **newp;
 
-	  for (newp = _environ; *newp++;);
+      char **newp;
+      for (newp = _environ; *newp++;);
 
-	  if (_dl_argv[-_dl_skip_args] == (char *) p)
+      if (newp != p || _dl_argv[0] != orig_argv0)
+	{
+	  if (orig_argv0 == (char *) p)
 	    {
 	      if ((char *) newp != _dl_argv[0])
 		{