linux-kernel - Re: ptrval hiding -- first kernel messages look rather "interesting"

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Date:   Fri, 1 Jun 2018 13:49:41 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joel Stanley <joel@....id.au>,
        "Tobin C. Harding" <me@...in.cc>, Jonathan Corbet <corbet@....net>
Subject: Re: ptrval hiding -- first kernel messages look rather "interesting"

On Fri, Jun 1, 2018 at 1:31 PM, Pavel Machek <pavel@....cz> wrote:
> Hi!
>
> v4.17 on n900:
>
> [    0.000000] Virtual kernel memory layout:
> [    0.000000]     vector  : 0xffff0000 - 0xffff1000   (   4 kB)
> [    0.000000]     fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)
> [    0.000000]     vmalloc : 0xd0000000 - 0xff800000   ( 760 MB)
> [    0.000000]     lowmem  : 0xc0000000 - 0xcff00000   ( 255 MB)
> [    0.000000]     pkmap   : 0xbfe00000 - 0xc0000000   (   2 MB)
> [    0.000000]     modules : 0xbf000000 - 0xbfe00000   (  14 MB)
> [    0.000000]       .text : 0x(ptrval) - 0x(ptrval)   (8160 kB)
> [    0.000000]       .init : 0x(ptrval) - 0x(ptrval)   (1024 kB)
> [    0.000000]       .data : 0x(ptrval) - 0x(ptrval)   ( 309 kB)
> [    0.000000]        .bss : 0x(ptrval) - 0x(ptrval)   ( 333 kB)
> [    0.000000] NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16
>
> I mean -- security is nice, but perhaps we should adjust the messages
> so this does not look like we are making fun of the user?

Colleague of mine (perhaps you even know him) wrote recently a small
patch that improves kernel by 400% by removing ptr_to_id() completely.

Okay, joking is joking, but it was a proposal to have some command
line option to enforce no-hash pointers.
I would rather enable it when one of the existing option is present
(like 'debug'), though it might alter the output in user space or
something else.
So, I have no strong opinion here.

-- 
With Best Regards,
Andy Shevchenko