linux-kernel - Re: [PATCH] x86: fix kaslr and memmap collision

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Date:   Tue, 3 Jan 2017 16:31:37 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Ingo Molnar <mingo@...nel.org>, Dave Jiang <dave.jiang@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        david <david@...morbit.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...1.01.org>,
        Kees Cook <keescook@...omium.org>, dyoung@...hat.com
Subject: Re: [PATCH] x86: fix kaslr and memmap collision

Hi Dan,

On 11/22/16 at 09:26am, Dan Williams wrote:
> [ replying for Dave since he's offline today and tomorrow ]
> 
> On Tue, Nov 22, 2016 at 12:47 AM, Ingo Molnar <mingo@...nel.org> wrote:
> >
> > * Dave Jiang <dave.jiang@...el.com> wrote:
> >
> >> CONFIG_RANDOMIZE_BASE relocates the kernel to a random base address.
> >> However it does not take into account the memmap= parameter passed in from
> >> the kernel commandline.
> >
> > memmap= parameters are often used as a list.
> >
> >> [...] This results in the kernel sometimes being put in the middle of the user
> >> memmap. [...]
> >
> > What does this mean? If memmap= is used to re-define the memory map then the
> > kernel getting in the middle of a RAM area is what we want, isn't it? What we
> > don't want is for the kernel to get into reserved areas, right?
> 
> Right, this is about teaching kaslr to not land the kernel in newly
> defined reserved regions that were not marked reserved in the initial
> e820 map from platform firmware.

If only tell kaslr to not land kernel in newly defined reserved regions,
memory added by "memmap=nn[KMG]@ss[KMG]" should not be avoided since
it's usable memory. Kernel randomized into this region is also what we
want. Not sure if I understand it right.

Thanks
Baoquan