[PATCH v4 09/10] mm: split ET_DYN ASLR from mmap ASLR

Kees Cook
2015-03-04T22:14:55Z

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
(e.g. 0x5... instead of 0x7f... on x86_64):

$ ./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.

Reported-by: Hector Marco-Gisbert <hecmargi@upv.es>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/arm/Kconfig | 1 -
arch/arm64/Kconfig | 1 -
arch/mips/Kconfig | 1 -
arch/powerpc/Kconfig | 1 -
arch/s390/include/asm/elf.h | 5 ++---
arch/s390/mm/mmap.c | 8 --------
arch/x86/Kconfig | 1 -
fs/Kconfig.binfmt | 3 ---
fs/binfmt_elf.c | 18 ++++--------------
9 files changed, 6 insertions(+), 33 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 248d99cabaa8..e2f0ef9c6ee3 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 5f469095e0e2..07e0fc7adc88 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 72ce5cece768..557c5f1772c1 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 14fe1c411489..910fa4f9ad1e 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 2e63de8aac7c..d0db9d944b6d 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 9aa91727fbf8..328be0fab910 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 995986b8e36b..6f08f5fa99dc 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>
@@ -909,21 +910,10 @@ 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);
}

error = elf_map(bprm->file, load_bias + vaddr, elf_ppnt,
--
1.9.1