mm: split ET_DYN ASLR from mmap ASLR

This fixes the "offset2lib" weakness in ASLR for arm, arm64, mips,
powerpc, and x86.  The problem is that if there is a leak of ASLR from
the executable (ET_DYN), it means a leak of shared library offset as
well (mmap), and vice versa.  Further details and a PoC of this attack
is available here:

  http://cybersecurity.upv.es/attacks/offset2lib/offset2lib.html

With this patch, a PIE linked executable (ET_DYN) has its own ASLR
region:

  $ ./show_mmaps_pie
  54859ccd6000-54859ccd7000 r-xp  ...  /tmp/show_mmaps_pie
  54859ced6000-54859ced7000 r--p  ...  /tmp/show_mmaps_pie
  54859ced7000-54859ced8000 rw-p  ...  /tmp/show_mmaps_pie
  7f75be764000-7f75be91f000 r-xp  ...  /lib/x86_64-linux-gnu/libc.so.6
  7f75be91f000-7f75beb1f000 ---p  ...  /lib/x86_64-linux-gnu/libc.so.6
  7f75beb1f000-7f75beb23000 r--p  ...  /lib/x86_64-linux-gnu/libc.so.6
  7f75beb23000-7f75beb25000 rw-p  ...  /lib/x86_64-linux-gnu/libc.so.6
  7f75beb25000-7f75beb2a000 rw-p  ...
  7f75beb2a000-7f75beb4d000 r-xp  ...  /lib64/ld-linux-x86-64.so.2
  7f75bed45000-7f75bed46000 rw-p  ...
  7f75bed46000-7f75bed47000 r-xp  ...
  7f75bed47000-7f75bed4c000 rw-p  ...
  7f75bed4c000-7f75bed4d000 r--p  ...  /lib64/ld-linux-x86-64.so.2
  7f75bed4d000-7f75bed4e000 rw-p  ...  /lib64/ld-linux-x86-64.so.2
  7f75bed4e000-7f75bed4f000 rw-p  ...
  7fffb3741000-7fffb3762000 rw-p  ...  [stack]
  7fffb377b000-7fffb377d000 r--p  ...  [vvar]
  7fffb377d000-7fffb377f000 r-xp  ...  [vdso]

The change is to add a call the newly created arch_mmap_rnd() into the
ELF loader for handling ET_DYN ASLR in a separate region from mmap ASLR,
as was already done on s390.  Removes CONFIG_BINFMT_ELF_RANDOMIZE_PIE,
which is no longer needed.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Hector Marco-Gisbert <hecmargi@upv.es>
Cc: Russell King <linux@arm.linux.org.uk>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: "David A. Long" <dave.long@linaro.org>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Arun Chandran <achandran@mvista.com>
Cc: Yann Droneaud <ydroneaud@opteya.com>
Cc: Min-Hua Chen <orca.chen@gmail.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Alex Smith <alex@alex-smith.me.uk>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: Vineeth Vijayan <vvijayan@mvista.com>
Cc: Jeff Bailey <jeffbailey@google.com>
Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Behan Webster <behanw@converseincode.com>
Cc: Ismael Ripoll <iripoll@upv.es>
Cc: Jan-Simon Mller <dl9pf@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

9 files changed, 6 insertions, 33 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index f85200a63a8b..4b62f4caf0ce 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1,7 +1,6 @@
 config ARM
         bool
         default y
-        select ARCH_BINFMT_ELF_RANDOMIZE_PIE
         select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
         select ARCH_HAS_ELF_RANDOMIZE
         select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7c1dbeb73e8d..34f487d5d84e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1,6 +1,5 @@
 config ARM64
         def_bool y
-        select ARCH_BINFMT_ELF_RANDOMIZE_PIE
         select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
         select ARCH_HAS_ELF_RANDOMIZE
         select ARCH_HAS_GCOV_PROFILE_ALL
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 688ce274f59d..a326c4cb8cf0 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -23,7 +23,6 @@ config MIPS
         select HAVE_KRETPROBES
         select HAVE_DEBUG_KMEMLEAK
         select HAVE_SYSCALL_TRACEPOINTS
-        select ARCH_BINFMT_ELF_RANDOMIZE_PIE
         select ARCH_HAS_ELF_RANDOMIZE
         select HAVE_ARCH_TRANSPARENT_HUGEPAGE if CPU_SUPPORTS_HUGEPAGES && 64BIT
         select RTC_LIB if !MACH_LOONGSON
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index fc5fffbb331b..e99014adf017 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -88,7 +88,6 @@ config PPC
         select ARCH_MIGHT_HAVE_PC_PARPORT
         select ARCH_MIGHT_HAVE_PC_SERIO
         select BINFMT_ELF
-        select ARCH_BINFMT_ELF_RANDOMIZE_PIE
         select ARCH_HAS_ELF_RANDOMIZE
         select OF
         select OF_EARLY_FLATTREE
diff --git a/arch/s390/include/asm/elf.h b/arch/s390/include/asm/elf.h
index f8db4781a4c2..ff662155b2c4 100644
--- a/arch/s390/include/asm/elf.h
+++ b/arch/s390/include/asm/elf.h
@@ -163,10 +163,9 @@ extern unsigned int vdso_enabled;
    the loader.  We need to make sure that it is out of the way of the program
    that it will "exec", and that there is sufficient room for the brk. 64-bit
    tasks are aligned to 4GB. */
-extern unsigned long randomize_et_dyn(void);
-#define ELF_ET_DYN_BASE (randomize_et_dyn() + (is_32bit_task() ? \
+#define ELF_ET_DYN_BASE (is_32bit_task() ? \
                                 (STACK_TOP / 3 * 2) : \
-                                (STACK_TOP / 3 * 2) & ~((1UL << 32) - 1)))
+                                (STACK_TOP / 3 * 2) & ~((1UL << 32) - 1))
 
 /* This yields a mask that user programs can use to figure out what
    instruction set this CPU supports. */
diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 8c11536f972d..bb3367c5cb0b 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -177,14 +177,6 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
         return addr;
 }
 
-unsigned long randomize_et_dyn(void)
-{
-        if (current->flags & PF_RANDOMIZE)
-                return arch_mmap_rnd();
-
-        return 0UL;
-}
-
 #ifndef CONFIG_64BIT
 
 /*
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 782ddbbc1c9a..1f7f185934a5 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -87,7 +87,6 @@ config X86
         select HAVE_ARCH_KMEMCHECK
         select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP
         select HAVE_USER_RETURN_NOTIFIER
-        select ARCH_BINFMT_ELF_RANDOMIZE_PIE
         select ARCH_HAS_ELF_RANDOMIZE
         select HAVE_ARCH_JUMP_LABEL
         select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index 270c48148f79..2d0cbbd14cfc 100644
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -27,9 +27,6 @@ config COMPAT_BINFMT_ELF
         bool
         depends on COMPAT && BINFMT_ELF
 
-config ARCH_BINFMT_ELF_RANDOMIZE_PIE
-        bool
-
 config ARCH_BINFMT_ELF_STATE
         bool
 
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index d925f55e4857..b20c05477e90 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -31,6 +31,7 @@
 #include <linux/security.h>
 #include <linux/random.h>
 #include <linux/elf.h>
+#include <linux/elf-randomize.h>
 #include <linux/utsname.h>
 #include <linux/coredump.h>
 #include <linux/sched.h>
@@ -910,21 +911,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
                          * default mmap base, as well as whatever program they
                          * might try to exec.  This is because the brk will
                          * follow the loader, and is not movable.  */
-#ifdef CONFIG_ARCH_BINFMT_ELF_RANDOMIZE_PIE
-                        /* Memory randomization might have been switched off
-                         * in runtime via sysctl or explicit setting of
-                         * personality flags.
-                         * If that is the case, retain the original non-zero
-                         * load_bias value in order to establish proper
-                         * non-randomized mappings.
-                         */
+                        load_bias = ELF_ET_DYN_BASE - vaddr;
                         if (current->flags & PF_RANDOMIZE)
-                                load_bias = 0;
-                        else
-                                load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
-#else
-                        load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
-#endif
+                                load_bias += arch_mmap_rnd();
+                        load_bias = ELF_PAGESTART(load_bias);
                         total_size = total_mapping_size(elf_phdata,
                                                         loc->elf_ex.e_phnum);
                         if (!total_size) {