Re: [PATCH 11/14] MIPS: memblock: Print out kernel virtual mem layout

[Matt Redfearn]

Hi Serge,



On 18/01/18 20:18, Serge Semin wrote:
> On Thu, Jan 18, 2018 at 12:03:03PM -0800, Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
> > On 01/17/2018 02:23 PM, Serge Semin wrote:
> > > It is useful to have the kernel virtual memory layout printed
> > > at boot time so to have the full information about the booted
> > > kernel. In some cases it might be unsafe to have virtual
> > > addresses freely visible in logs, so the %pK format is used if
> > > one want to hide them.
> > >
> > > Signed-off-by: Serge Semin <fancer.lancer@xxxxxxxxx>
> >
> > I personally like having that information because that helps debug and
> > have a quick reference, but there appears to be a trend to remove this
> > in the name of security:
> >
> > https://patchwork.kernel.org/patch/10124007/
> >
> > maybe hide this behind a configuration option?
>
> Yeah, arm code was the place I picked the function up.) But in my case
> I've used %pK so the pointers would disappear from logging when
> kptr_restrict sysctl is 1 or 2.
> I agree, that we might need to make the printouts optional. If there is
> any kernel config, which for instance increases the kernel security we
> could also use it or anything else to discard the printouts at compile
> time.


Certainly, when KASLR is active it would be preferable to hide this 
information, so you could use CONFIG_RELOCATABLE. The existing KASLR 
stuff additionally hides this kind of information behind 
CONFIG_DEBUG_KERNEL, so that only people actively debugging the kernel 
see it:

http://elixir.free-electrons.com/linux/v4.15-rc8/source/arch/mips/kernel/setup.c#L604

Thanks,
Matt

> > --
> > Florian