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SubjectRe: [PATCH] Fix offset2lib issue for x86*, ARM*, PowerPC and MIPS
From
(I've added some additional CCs to make sure the arch maintainers
notice this patch.)

This patch seems white-space damaged to me. I had to do a lot of
manual editing to get it to apply. Please use "git format-patch", if
you're not already. What version of the kernel was this based on?

On Mon, Feb 23, 2015 at 10:37 AM, Hector Marco <hecmargi@upv.es> wrote:
> [PATCH] Fix offset2lib issue for x86*, ARM*, PowerPC and MIPS
>
> The issue appears on PIE linked executables when all memory areas of a
> process are randomized. In this case, the attack "offset2lib" de-randomizes
> all library areas on 64 bit Linux systems in less than one second.
>
>
> Further details of the PoC attack at:
> http://cybersecurity.upv.es/attacks/offset2lib/offset2lib.html
>
>
> This patch loads the PIE linked executable in a different area than the
> libraries. The successful fix can be tested with a simple pie compiled
> application:
>
>
> $ ./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]
>
>
> Once corrected, the PIE linked application is loaded in a different area.

Thanks for working on this!

>
> We updated the "Fixing Offset2lib weakness" page:
> http://cybersecurity.upv.es/solutions/aslrv2/aslrv2.html
>
>
> Signed-off-by: Hector Marco-Gisbert <hecmargi@upv.es>
> Signed-off-by: Ismael Ripoll <iripoll@upv.es>

Acked-by: Kees Cook <keescook@chromium.org>

>
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 97d07ed..ee7ea7e 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_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> select ARCH_HAVE_CUSTOM_GPIO_H
> diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
> index afb9caf..6755cd8 100644
> --- a/arch/arm/include/asm/elf.h
> +++ b/arch/arm/include/asm/elf.h
> @@ -115,7 +115,8 @@ int dump_task_regs(struct task_struct *t, elf_gregset_t
> *elfregs);
> 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. */
>
> -#define ELF_ET_DYN_BASE (2 * TASK_SIZE / 3)
> +extern unsigned long randomize_et_dyn(unsigned long base);
> +#define ELF_ET_DYN_BASE (randomize_et_dyn(2 * TASK_SIZE / 3))
>
> /* When the program starts, a1 contains a pointer to a function to be
> registered with atexit, as per the SVR4 ABI. A value of 0 means we
> diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
> index 5e85ed3..9177100 100644
> --- a/arch/arm/mm/mmap.c
> +++ b/arch/arm/mm/mmap.c
> @@ -30,6 +30,17 @@ static int mmap_is_legacy(void)
> return sysctl_legacy_va_layout;
> }
>
> +static unsigned long mmap_rnd(void)
> +{
> + unsigned long rnd = 0;
> +
> + /* 8 bits of randomness in 20 address space bits */
> + if (current->flags & PF_RANDOMIZE)
> + rnd = (long)get_random_int() % (1 << 8);
> +
> + return rnd << PAGE_SHIFT;
> +}
> +
> static unsigned long mmap_base(unsigned long rnd)
> {
> unsigned long gap = rlimit(RLIMIT_STACK);
> @@ -230,3 +241,13 @@ int devmem_is_allowed(unsigned long pfn)
> }
>
> #endif
> +
> +unsigned long randomize_et_dyn(unsigned long base)
> +{
> + unsigned long ret;
> + if ((current->personality & ADDR_NO_RANDOMIZE) ||
> + !(current->flags & PF_RANDOMIZE))
> + return base;
> + ret = base + mmap_rnd();
> + return (ret > base) ? ret : base;
> +}
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b1f9a20..5580d90 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_GCOV_PROFILE_ALL
> select ARCH_HAS_SG_CHAIN
> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> index 1f65be3..01d3aab 100644
> --- a/arch/arm64/include/asm/elf.h
> +++ b/arch/arm64/include/asm/elf.h
> @@ -126,7 +126,7 @@ typedef struct user_fpsimd_state elf_fpregset_t;
> * that it will "exec", and that there is sufficient room for the brk.
> */
> extern unsigned long randomize_et_dyn(unsigned long base);
> -#define ELF_ET_DYN_BASE (2 * TASK_SIZE_64 / 3)
> +#define ELF_ET_DYN_BASE (randomize_et_dyn(2 * TASK_SIZE_64 / 3))
>
> /*
> * When the program starts, a1 contains a pointer to a function to be
> @@ -169,7 +169,7 @@ extern unsigned long arch_randomize_brk(struct mm_struct
> *mm);
> #define COMPAT_ELF_PLATFORM ("v8l")
> #endif
>
> -#define COMPAT_ELF_ET_DYN_BASE (2 * TASK_SIZE_32 / 3)
> +#define COMPAT_ELF_ET_DYN_BASE (randomize_et_dyn(2 * TASK_SIZE_32 /
> 3))
>
> /* AArch32 registers. */
> #define COMPAT_ELF_NGREG 18
> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index 54922d1..980110c50 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -89,6 +89,16 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
> }
> EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
>
> +unsigned long randomize_et_dyn(unsigned long base)
> +{
> + unsigned long ret;
> + if ((current->personality & ADDR_NO_RANDOMIZE) ||
> + !(current->flags & PF_RANDOMIZE))
> + return base;
> + ret = base + mmap_rnd();
> + return (ret > base) ? ret : base;
> +}
> +
>
> /*
> * You really shouldn't be using read() or write() on /dev/mem. This might
> go
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 3289969..31cc248 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 HAVE_ARCH_TRANSPARENT_HUGEPAGE if CPU_SUPPORTS_HUGEPAGES &&
> 64BIT
> select RTC_LIB if !MACH_LOONGSON
> select GENERIC_ATOMIC64 if !64BIT
> diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
> index eb4d95d..fcac4c99 100644
> --- a/arch/mips/include/asm/elf.h
> +++ b/arch/mips/include/asm/elf.h
> @@ -402,7 +402,8 @@ extern const char *__elf_platform;
> that it will "exec", and that there is sufficient room for the brk. */
>
> #ifndef ELF_ET_DYN_BASE
> -#define ELF_ET_DYN_BASE (TASK_SIZE / 3 * 2)
> +extern unsigned long randomize_et_dyn(unsigned long base);
> +#define ELF_ET_DYN_BASE (randomize_et_dyn(TASK_SIZE / 3 *
> 2))
> #endif
>
> #define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
> diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> index f1baadd..20ad644 100644
> --- a/arch/mips/mm/mmap.c
> +++ b/arch/mips/mm/mmap.c
> @@ -196,3 +196,13 @@ int __virt_addr_valid(const volatile void *kaddr)
> return pfn_valid(PFN_DOWN(virt_to_phys(kaddr)));
> }
> EXPORT_SYMBOL_GPL(__virt_addr_valid);
> +
> +unsigned long randomize_et_dyn(unsigned long base)
> +{
> + unsigned long ret;
> + if ((current->personality & ADDR_NO_RANDOMIZE) ||
> + !(current->flags & PF_RANDOMIZE))
> + return base;
> + ret = base + brk_rnd();
> + return (ret > base) ? ret : base;
> +}
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index a2a168e..fa4c877 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 OF
> select OF_EARLY_FLATTREE
> select OF_RESERVED_MEM
> diff --git a/arch/powerpc/include/asm/elf.h b/arch/powerpc/include/asm/elf.h
> index 57d289a..4080425 100644
> --- a/arch/powerpc/include/asm/elf.h
> +++ b/arch/powerpc/include/asm/elf.h
> @@ -28,7 +28,8 @@
> 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. */
>
> -#define ELF_ET_DYN_BASE 0x20000000
> +extern unsigned long randomize_et_dyn(unsigned long base);
> +#define ELF_ET_DYN_BASE (randomize_et_dyn(0x20000000))
>
> #define ELF_CORE_EFLAGS (is_elf2_task() ? 2 : 0)
>
> diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
> index cb8bdbe..3e642e7 100644
> --- a/arch/powerpc/mm/mmap.c
> +++ b/arch/powerpc/mm/mmap.c
> @@ -97,3 +97,13 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
> mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> }
> }
> +
> +unsigned long randomize_et_dyn(unsigned long base)
> +{
> + unsigned long ret;
> + if ((current->personality & ADDR_NO_RANDOMIZE) ||
> + !(current->flags & PF_RANDOMIZE))
> + return base;
> + ret = base + mmap_rnd();
> + return (ret > base) ? ret : base;
> +}
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index ba397bd..dcfe16c 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -85,7 +85,6 @@ config X86
> select HAVE_CMPXCHG_DOUBLE
> select HAVE_ARCH_KMEMCHECK
> select HAVE_USER_RETURN_NOTIFIER
> - select ARCH_BINFMT_ELF_RANDOMIZE_PIE
> select HAVE_ARCH_JUMP_LABEL
> select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
> select SPARSE_IRQ
> diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> index ca3347a..92c6ac4 100644
> --- a/arch/x86/include/asm/elf.h
> +++ b/arch/x86/include/asm/elf.h
> @@ -249,7 +249,8 @@ extern int force_personality32;
> 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. */
>
> -#define ELF_ET_DYN_BASE (TASK_SIZE / 3 * 2)
> +extern unsigned long randomize_et_dyn(unsigned long base);
> +#define ELF_ET_DYN_BASE (randomize_et_dyn(TASK_SIZE / 3 *
> 2))
>
> /* This yields a mask that user programs can use to figure out what
> instruction set this CPU supports. This could be done in user space,
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 919b912..7b86605 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -122,3 +122,12 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
> mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> }
> }
> +unsigned long randomize_et_dyn(unsigned long base)
> +{
> + unsigned long ret;
> + if ((current->personality & ADDR_NO_RANDOMIZE) ||
> + !(current->flags & PF_RANDOMIZE))
> + return base;
> + ret = base + mmap_rnd();
> + return (ret > base) ? ret : base;
> +}
> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
> index c055d56..1186190 100644
> --- a/fs/Kconfig.binfmt
> +++ b/fs/Kconfig.binfmt
> @@ -27,8 +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 02b1691..72f7ff5 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -908,21 +908,7 @@ 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.
> - */
> - 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
> }
>
> error = elf_map(bprm->file, load_bias + vaddr, elf_ppnt,

I think this is much cleaner now without
ARCH_BINFMT_ELF_RANDOMIZE_PIE. I imagine there could be some follow-up
cleanups to standardize (or at least clearly document) the intended
levels of entropy in the 4 ASLR regions on each architecture, as it
currently varies a bit.

Thanks!

-Kees

--
Kees Cook
Chrome OS Security


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