linux-kernel - Re: [PATCH] arm64: kaslr: Reserve size of ARM64_MEMSTART

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Message-ID: <CAKv+Gu-YTdQmhU_br4amNZYn12=6Amr7w=wP57DyNn7_axptCg@mail.gmail.com>
Date:   Wed, 26 Dec 2018 14:49:58 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Yueyi Li <liyueyi@...e.com>
Cc:     "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "markus@...rhumer.com" <markus@...rhumer.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: kaslr: Reserve size of ARM64_MEMSTART_ALIGN in
 linear region

On Tue, 25 Dec 2018 at 03:30, Yueyi Li <liyueyi@...e.com> wrote:
>
> Hi Ard,
>
>
> On 2018/12/24 17:45, Ard Biesheuvel wrote:
> > Does the following change fix your issue as well?
> >
> > index 9b432d9fcada..9dcf0ff75a11 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -447,7 +447,7 @@ void __init arm64_memblock_init(void)
> >                   * memory spans, randomize the linear region as well.
> >                   */
> >                  if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
> > -                       range = range / ARM64_MEMSTART_ALIGN + 1;
> > +                       range /= ARM64_MEMSTART_ALIGN;
> >                          memstart_addr -= ARM64_MEMSTART_ALIGN *
> >                                           ((range * memstart_offset_seed) >> 16);
> >                  }
>
> Yes, it can fix this also. I just think modify the first *range*
> calculation would be easier to grasp, what do you think?
>

I don't think there is a difference, to be honest, but I will leave it
up to the maintainers to decide which approach they prefer.