mm: fold arch_randomize_brk into ARCH_HAS_ELF_RANDOMIZE

The arch_randomize_brk() function is used on several architectures,
even those that don't support ET_DYN ASLR. To avoid bulky extern/#define
tricks, consolidate the support under CONFIG_ARCH_HAS_ELF_RANDOMIZE for
the architectures that support it, while still handling CONFIG_COMPAT_BRK.

Signed-off-by: Kees Cook <[e-mail]>
Cc: Hector Marco-Gisbert <[e-mail]>
Cc: Russell King <[e-mail]>
Reviewed-by: Ingo Molnar <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: "David A. Long" <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Arun Chandran <[e-mail]>
Cc: Yann Droneaud <[e-mail]>
Cc: Min-Hua Chen <[e-mail]>
Cc: Paul Burton <[e-mail]>
Cc: Alex Smith <[e-mail]>
Cc: Markos Chandras <[e-mail]>
Cc: Vineeth Vijayan <[e-mail]>
Cc: Jeff Bailey <[e-mail]>
Cc: Michael Holzheu <[e-mail]>
Cc: Ben Hutchings <[e-mail]>
Cc: Behan Webster <[e-mail]>
Cc: Ismael Ripoll <[e-mail]>
Cc: Jan-Simon Mller <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/Kconfig

···
 	  An architecture supports choosing randomized locations for
 	  stack, mmap, brk, and ET_DYN. Defined functions:
 	  - arch_mmap_rnd()
+	  - arch_randomize_brk()
 
 #
 # ABI hall of shame

arch/arm/include/asm/elf.h

···
 extern void elf_set_personality(const struct elf32_hdr *);
 #define SET_PERSONALITY(ex)	elf_set_personality(&(ex))
 
-struct mm_struct;
-extern unsigned long arch_randomize_brk(struct mm_struct *mm);
-#define arch_randomize_brk arch_randomize_brk
-
 #ifdef CONFIG_MMU
 #define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
 struct linux_binprm;

arch/arm64/include/asm/elf.h

···
 #define STACK_RND_MASK			(0x3ffff >> (PAGE_SHIFT - 12))
 #endif
 
-struct mm_struct;
-extern unsigned long arch_randomize_brk(struct mm_struct *mm);
-#define arch_randomize_brk arch_randomize_brk
-
 #ifdef CONFIG_COMPAT
 
 #ifdef __AARCH64EB__

arch/mips/include/asm/elf.h

···
 extern int arch_setup_additional_pages(struct linux_binprm *bprm,
 				       int uses_interp);
 
-struct mm_struct;
-extern unsigned long arch_randomize_brk(struct mm_struct *mm);
-#define arch_randomize_brk arch_randomize_brk
-
 struct arch_elf_state {
 	int fp_abi;
 	int interp_fp_abi;

arch/powerpc/include/asm/elf.h

···
 	(0x7ff >> (PAGE_SHIFT - 12)) : \
 	(0x3ffff >> (PAGE_SHIFT - 12)))
 
-extern unsigned long arch_randomize_brk(struct mm_struct *mm);
-#define arch_randomize_brk arch_randomize_brk
-
-
 #ifdef CONFIG_SPU_BASE
 /* Notes used in ET_CORE. Note name is "SPU/<fd>/<filename>". */
 #define NT_SPU		1

arch/s390/include/asm/elf.h

···
 #define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
 int arch_setup_additional_pages(struct linux_binprm *, int);
 
-extern unsigned long arch_randomize_brk(struct mm_struct *mm);
-#define arch_randomize_brk arch_randomize_brk
-
 void *fill_cpu_elf_notes(void *ptr, struct save_area *sa, __vector128 *vxrs);
 
 #endif

arch/x86/include/asm/elf.h

···
 					      int uses_interp);
 #define compat_arch_setup_additional_pages compat_arch_setup_additional_pages
 
-extern unsigned long arch_randomize_brk(struct mm_struct *mm);
-#define arch_randomize_brk arch_randomize_brk
-
 /*
  * True on X86_32 or when emulating IA32 on X86_64
  */

fs/binfmt_elf.c

···
 	current->mm->end_data = end_data;
 	current->mm->start_stack = bprm->p;
 
-#ifdef arch_randomize_brk
 	if ((current->flags & PF_RANDOMIZE) && (randomize_va_space > 1)) {
 		current->mm->brk = current->mm->start_brk =
 			arch_randomize_brk(current->mm);
-#ifdef CONFIG_COMPAT_BRK
+#ifdef compat_brk_randomized
 		current->brk_randomized = 1;
 #endif
 	}
-#endif
 
 	if (current->personality & MMAP_PAGE_ZERO) {
 		/* Why this, you ask???  Well SVr4 maps page 0 as read-only,

include/linux/elf-randomize.h

···
 #ifndef _ELF_RANDOMIZE_H
 #define _ELF_RANDOMIZE_H
 
+struct mm_struct;
+
 #ifndef CONFIG_ARCH_HAS_ELF_RANDOMIZE
 static inline unsigned long arch_mmap_rnd(void) { return 0; }
+# if defined(arch_randomize_brk) && defined(CONFIG_COMPAT_BRK)
+#  define compat_brk_randomized
+# endif
+# ifndef arch_randomize_brk
+#  define arch_randomize_brk(mm)	(mm->brk)
+# endif
 #else
 extern unsigned long arch_mmap_rnd(void);
+extern unsigned long arch_randomize_brk(struct mm_struct *mm);
+# ifdef CONFIG_COMPAT_BRK
+#  define compat_brk_randomized
+# endif
 #endif
 
 #endif