Re: [PATCH 1/2] x86: fix norandmaps

Dmitry Safonov
2017-07-10T11:56:30Z

On 07/10/2017 02:14 PM, Oleg Nesterov wrote:
> 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.
>
> 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>

Thanks, Oleg,
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>

> ---
> arch/x86/mm/mmap.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 19ad095..6369d04 100644
> --- 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);
> }
>
>

--
Dmitry