Re: [PATCH] mm: Revert x86_64 and arm64 ELF_ET_DYN_BASE base
From: Will Deacon
Date: Tue Aug 08 2017 - 05:34:54 EST
On Mon, Aug 07, 2017 at 01:15:42PM -0700, Kees Cook wrote:
> Moving the x86_64 and arm64 PIE base from 0x555555554000 to 0x000100000000
> broke AddressSanitizer. This is a partial revert of:
>
> commit eab09532d400 ("binfmt_elf: use ELF_ET_DYN_BASE only for PIE")
> commit 02445990a96e ("arm64: move ELF_ET_DYN_BASE to 4GB / 4MB")
>
> The AddressSanitizer tool has hard-coded expectations about where
> executable mappings are loaded. The motivation for changing the PIE
> base in the above commits was to avoid the Stack-Clash CVEs that
> allowed executable mappings to get too close to heap and stack. This
> was mainly a problem on 32-bit, but the 64-bit bases were moved too,
> in an effort to proactively protect those systems (proofs of concept
> do exist that show 64-bit collisions, but other recent changes to fix
> stack accounting and setuid behaviors will minimize the impact).
>
> The new 32-bit PIE base is fine for ASan (since it matches the ET_EXEC
> base), so only the 64-bit PIE base needs to be reverted to let x86 and
> arm64 ASan binaries run again. Future changes to the 64-bit PIE base on
> these architectures can be made optional once a more dynamic method for
> dealing with AddressSanitizer is found. (e.g. always loading PIE into
> the mmap region for marked binaries.)
>
> Reported-by: Kostya Serebryany <kcc@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> arch/arm64/include/asm/elf.h | 4 ++--
> arch/x86/include/asm/elf.h | 4 ++--
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> index acae781f7359..3288c2b36731 100644
> --- a/arch/arm64/include/asm/elf.h
> +++ b/arch/arm64/include/asm/elf.h
> @@ -114,10 +114,10 @@
>
> /*
> * This is the base location for PIE (ET_DYN with INTERP) loads. On
> - * 64-bit, this is raised to 4GB to leave the entire 32-bit address
> + * 64-bit, this is above 4GB to leave the entire 32-bit address
> * space open for things that want to use the area for 32-bit pointers.
> */
> -#define ELF_ET_DYN_BASE 0x100000000UL
> +#define ELF_ET_DYN_BASE (2 * TASK_SIZE_64 / 3)
>
> #ifndef __ASSEMBLY__
Acked-by: Will Deacon <will.deacon@xxxxxxx>
I assume this is going via akpm like the original commit?
Will