[PATCH] NX: allow architectures to select legacy mode dynamically

On some platforms, you'll want to support READ_IMPLIES_EXEC differently
depending on personality (e.g, native binary vs. x86 binary).

This supports that (and makes the code more readable while at it) by
replacing the old architecture-specific fixed LEGACY_BINARIES macro
define with a architecture-specific "elf_read_implies_exec_binary()"
helper function.

For now, x86 is the only user, and sets the "read implies exec" bit for
legacy apps.  ia64 and x86-64 are likely to want to do their own thing.

Acked by Ingo.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/binfmt_elf.c

@@ -492,7 +492,7 @@ static int load_elf_binary(struct linux_binprm * bprm, struct pt_regs * regs)
   	struct exec interp_ex;
 	char passed_fileno[6];
 	struct files_struct *files;
-	int executable_stack = EXSTACK_DEFAULT;
+	int have_pt_gnu_stack, executable_stack = EXSTACK_DEFAULT;
 	unsigned long def_flags = 0;
 	
 	/* Get the exec-header */
@@ -627,10 +627,7 @@ static int load_elf_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 				executable_stack = EXSTACK_DISABLE_X;
 			break;
 		}
-#ifdef LEGACY_BINARIES
-	if (i == elf_ex.e_phnum)
-		current->personality |= READ_IMPLIES_EXEC;
-#endif
+	have_pt_gnu_stack = (i < elf_ex.e_phnum);
 
 	/* Some simple consistency checks for the interpreter */
 	if (elf_interpreter) {
@@ -703,6 +700,8 @@ static int load_elf_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 	/* Do this immediately, since STACK_TOP as used in setup_arg_pages
 	   may depend on the personality.  */
 	SET_PERSONALITY(elf_ex, ibcs2_interpreter);
+	if (elf_read_implies_exec(elf_ex, have_pt_gnu_stack))
+		current->personality |= READ_IMPLIES_EXEC;
 
 	/* Do this so that we can load the interpreter, if need be.  We will
 	   change some of these later */

include/asm-i386/elf.h

@@ -120,10 +120,10 @@ typedef struct user_fxsr_struct elf_fpxregset_t;
 #define SET_PERSONALITY(ex, ibcs2) do { } while (0)
 
 /*
- * A legacy binary, when loaded by the ELF loader, will have the
- * READ_IMPLIES_EXEC personality flag set automatically:
+ * An executable for which elf_read_implies_exec() returns TRUE will
+ * have the READ_IMPLIES_EXEC personality flag set automatically.
  */
-#define LEGACY_BINARIES
+#define elf_read_implies_exec_binary(ex, have_pt_gnu_stack)	(!(have_pt_gnu_stack))
 
 extern int dump_task_regs (struct task_struct *, elf_gregset_t *);
 extern int dump_task_fpu (struct task_struct *, elf_fpregset_t *);

include/linux/elf.h

@@ -4,6 +4,13 @@
 #include <linux/types.h>
 #include <asm/elf.h>
 
+#ifndef elf_read_implies_exec
+  /* Executables for which elf_read_implies_exec() returns TRUE will
+     have the READ_IMPLIES_EXEC personality flag set automatically.
+     Override in asm/elf.h as needed.  */
+# define elf_read_implies_exec(ex, have_pt_gnu_stack)	0
+#endif
+
 /* 32-bit ELF base types. */
 typedef __u32	Elf32_Addr;
 typedef __u16	Elf32_Half;