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@xxxxxx> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- 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
