• Kees Cook's avatar
    mm: revert x86_64 and arm64 ELF_ET_DYN_BASE base changes · c715b72c
    Kees Cook authored
    Moving the x86_64 and arm64 PIE base from 0x555555554000 to 0x000100000000
    broke AddressSanitizer.  This is a partial revert of:
    
      eab09532 ("binfmt_elf: use ELF_ET_DYN_BASE only for PIE")
      02445990 ("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.)
    
    Link: http://lkml.kernel.org/r/20170807201542.GA21271@beast
    Fixes: eab09532 ("binfmt_elf: use ELF_ET_DYN_BASE only for PIE")
    Fixes: 02445990 ("arm64: move ELF_ET_DYN_BASE to 4GB / 4MB")
    Signed-off-by: default avatarKees Cook <keescook@chromium.org>
    Reported-by: default avatarKostya Serebryany <kcc@google.com>
    Acked-by: default avatarWill Deacon <will.deacon@arm.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    c715b72c
elf.h 10.7 KB