2003-09-23 Roland McGrath <roland@redhat.com>

	* sysdeps/generic/ldsodefs.h (struct rtld_global): Add _dl_stack_flags
	and _dl_make_stack_executable_hook.  Declare _dl_make_stack_executable.
	* elf/rtld.c (_rtld_global): Add initializer for _dl_stack_flags.
	(dl_main): Reset _dl_stack_flags according to PT_GNU_STACK phdr.
	Initialize _dl_make_stack_executable_hook.
	* elf/dl-support.c: Define those new variables.
	(_dl_non_dynamic_init): Scan phdrs for PT_GNU_STACK.
	(_dl_phdr): Fix type.
	* elf/dl-load.c (_dl_map_object_from_fd): Grok PT_GNU_STACK phdr and
	enable execute permission for the stack if necessary.
	* sysdeps/generic/dl-execstack.c: New file.
	* elf/Makefile (dl-routines): Add it.
	* elf/Versions (ld: GLIBC_PRIVATE): Add _dl_make_stack_executable.
	* sysdeps/unix/sysv/linux/dl-execstack.c: New file.

4 files changed, 50 insertions, 1 deletions

diff --git a/elf/Versions b/elf/Versions
index 7b07999..d3ed536 100644
--- a/elf/Versions
+++ b/elf/Versions
@@ -54,5 +54,6 @@ ld {
     _rtld_global; _dl_tls_symaddr; _dl_allocate_tls; _dl_deallocate_tls;
     _dl_get_tls_static_info; _dl_allocate_tls_init;
     _dl_get_origin; _dl_tls_setup; _dl_rtld_di_serinfo;
+    _dl_make_stack_executable;
   }
 }
diff --git a/elf/dl-load.c b/elf/dl-load.c
index 249ef84..0b6e96f 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -904,6 +904,9 @@ _dl_map_object_from_fd (const char *name, int fd, struct filebuf *fbp,
 	}
     }
 
+  /* Presumed absent PT_GNU_STACK.  */
+  uint_fast16_t stack_flags = PF_R|PF_W|PF_X;
+
   {
     /* Scan the program header table, collecting its load commands.  */
     struct loadcmd
@@ -1058,6 +1061,10 @@ cannot allocate TLS data structures for initial thread");
 	  errstring = N_("cannot handle TLS data");
 	  goto call_lose;
 	  break;
+
+	case PT_GNU_STACK:
+	  stack_flags = ph->p_flags;
+	  break;
 	}
 
     if (__builtin_expect (nloadcmds == 0, 0))
@@ -1334,6 +1341,19 @@ cannot allocate TLS data structures for initial thread");
   l->l_dev = st.st_dev;
   l->l_ino = st.st_ino;
 
+  if (__builtin_expect ((stack_flags &~ GL(dl_stack_flags)) & PF_X, 0))
+    {
+      /* The stack is presently not executable, but this module
+	 requires that it be executable.  */
+      errval = (*GL(dl_make_stack_executable_hook)) ();
+      if (errval)
+	{
+	  errstring = N_("\
+cannot enable executable stack as shared object requires");
+	  goto call_lose;
+	}
+    }
+
   /* When we profile the SONAME might be needed for something else but
      loading.  Add it right away.  */
   if (__builtin_expect (GL(dl_profile) != NULL, 0)
diff --git a/elf/dl-support.c b/elf/dl-support.c
index 8c58b2b..448f4c6 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -129,6 +129,16 @@ ElfW(Phdr) *_dl_phdr;
 size_t _dl_phnum;
 unsigned long int _dl_hwcap __attribute__ ((nocommon));
 
+/* Prevailing state of the stack, PF_X indicating it's executable.  */
+ElfW(Word) _dl_stack_flags = PF_R|PF_W|PF_X;
+
+/* If loading a shared object requires that we make the stack executable
+   when it was not, we do it by calling this function.
+   It returns an errno code or zero on success.  */
+int (*_dl_make_stack_executable_hook) (void) internal_function
+  = _dl_make_stack_executable;
+
+
 #ifdef NEED_DL_SYSINFO
 /* Needed for improved syscall handling on at least x86/Linux.  */
 uintptr_t _dl_sysinfo = DL_SYSINFO_DEFAULT;
@@ -264,6 +274,15 @@ _dl_non_dynamic_init (void)
   /* Now determine the length of the platform string.  */
   if (_dl_platform != NULL)
     _dl_platformlen = strlen (_dl_platform);
+
+  /* Scan for a program header telling us the stack is nonexecutable.  */
+  if (_dl_phdr != NULL)
+    for (uint_fast16_t i = 0; i < _dl_phnum; ++i)
+      if (_dl_phdr[i].p_type == PT_GNU_STACK)
+	{
+	  _dl_stack_flags = _dl_phdr[i].p_flags;
+	  break;
+	}
 }
 
 
diff --git a/elf/rtld.c b/elf/rtld.c
index 8f9fc7c..c17f621 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -98,6 +98,8 @@ struct rtld_global _rtld_global =
     ._dl_fpu_control = _FPU_DEFAULT,
     ._dl_correct_cache_id = _DL_CACHE_DEFAULT_ID,
     ._dl_hwcap_mask = HWCAP_IMPORTANT,
+    /* Default presumption without further information is executable stack.  */
+    ._dl_stack_flags = PF_R|PF_W|PF_X,
 #ifdef _LIBC_REENTRANT
     ._dl_load_lock = _RTLD_LOCK_RECURSIVE_INITIALIZER
 #endif
@@ -249,7 +251,7 @@ _dl_start_final (void *arg, struct dl_start_final_info *info)
      file access.  It will call `dl_main' (below) to do all the real work
      of the dynamic linker, and then unwind our frame and run the user
      entry point on the same stack we entered on.  */
-  start_addr =  _dl_sysdep_start (arg, &dl_main);
+  start_addr = _dl_sysdep_start (arg, &dl_main);
 
 #ifndef HP_TIMING_NONAVAIL
   if (HP_TIMING_AVAIL)
@@ -903,6 +905,9 @@ of this helper program; chances are you did not intend to run this program.\n\
 	  }
 	break;
 #endif
+      case PT_GNU_STACK:
+	GL(dl_stack_flags) = ph->p_flags;
+	break;
       }
 #ifdef USE_TLS
     /* Adjust the address of the TLS initialization image in case
@@ -949,6 +954,10 @@ of this helper program; chances are you did not intend to run this program.\n\
       _exit (has_interp ? 0 : 2);
     }
 
+  /* The explicit initialization here is cheaper than processing the reloc
+     in the _rtld_local definition's initializer.  */
+  GL(dl_make_stack_executable_hook) = &_dl_make_stack_executable;
+
   if (! rtld_is_main)
     /* Initialize the data structures for the search paths for shared
        objects.  */