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    Subject[PATCH 4.12 30/41] x86: Fix norandmaps/ADDR_NO_RANDOMIZE
    Date
    4.12-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Oleg Nesterov <oleg@redhat.com>

    commit 47ac5484fd961420e5ec0bb5b972fde381f57365 upstream.

    Documentation/admin-guide/kernel-parameters.txt says:

    norandmaps Don't use address space randomization. Equivalent
    to echo 0 > /proc/sys/kernel/randomize_va_space

    but it doesn't work because arch_rnd() which is used to randomize
    mm->mmap_base returns a random value unconditionally. And as Kirill
    pointed out, ADDR_NO_RANDOMIZE is broken by the same reason.

    Just shift the PF_RANDOMIZE check from arch_mmap_rnd() to arch_rnd().

    Fixes: 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()")
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
    Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Link: http://lkml.kernel.org/r/20170815153952.GA1076@redhat.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/mm/mmap.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/arch/x86/mm/mmap.c
    +++ b/arch/x86/mm/mmap.c
    @@ -82,13 +82,13 @@ static int mmap_is_legacy(void)

    static unsigned long arch_rnd(unsigned int rndbits)
    {
    + if (!(current->flags & PF_RANDOMIZE))
    + return 0;
    return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
    }

    unsigned long arch_mmap_rnd(void)
    {
    - if (!(current->flags & PF_RANDOMIZE))
    - return 0;
    return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
    }


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