linux-kernel - Re: [PATCH 0/2] Determine kernel text mapping size at runtime for x86

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Date:   Thu, 8 Dec 2016 10:31:47 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>, Yinghai Lu <yinghai@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Thomas Garnier <thgarnie@...gle.com>,
        Alexander Kuleshov <kuleshovmail@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Anderson <anderson@...hat.com>,
        Dave Young <dyoung@...hat.com>, Xunlei Pang <xlpang@...hat.com>
Subject: Re: [PATCH 0/2] Determine kernel text mapping size at runtime for x86_64

On Wed, Dec 7, 2016 at 11:56 PM, Baoquan He <bhe@...hat.com> wrote:
> Dave Anderson ever told in Crash utility he makes judgement whether it's
> a kaslr kernel by size of KERNEL_IMAGE_SIZE. As long as it's 1G, it's
> recognized as kaslr. Then the current upstream kernel has a wrong behaviour,
> it sets KERNEL_IMAGE_SIZE as 1G as long as CONFIG_RANDOMIZE_BASE is enabled,
> though people specify "nokaslr" into cmdline to disable kaslr explicitly.

I'm not sure that's the correct solution to the Crash utility -- the
kaslr-ness of a kernel should be already exposed in the dump with the
kaslr_enabled variable yes?

> So in this patchset, made changes to determine the size of kernel text mapping
> area at runtime. If "nokaslr" specified, kernel mapping size is 512M though
> CONFIG_RANDOMIZE_BASE is enabled.

This seems to make the non-KASLR case more consistent, so I'm fine
with the idea. Once the build-bots are happy with everything, consider
the series:

Acked-by: Kees Cook <keescook@...omium.org>

Thanks!

-Kees

>
> Baoquan He (2):
>   x86/64: Make kernel text mapping always take one whole page table in
>     early boot code
>   x86/KASLR/64: Determine kernel text mapping size at runtime
>
>  arch/x86/boot/compressed/kaslr.c        | 15 ++++++++++-----
>  arch/x86/include/asm/kaslr.h            |  1 +
>  arch/x86/include/asm/page_64_types.h    | 20 ++++++++++++--------
>  arch/x86/include/asm/pgtable_64_types.h |  2 +-
>  arch/x86/kernel/head64.c                | 11 ++++++-----
>  arch/x86/kernel/head_64.S               | 16 +++++++++-------
>  arch/x86/mm/dump_pagetables.c           |  3 ++-
>  arch/x86/mm/init_64.c                   |  2 +-
>  arch/x86/mm/physaddr.c                  |  6 +++---
>  9 files changed, 45 insertions(+), 31 deletions(-)
>
> --
> 2.5.5
>



-- 
Kees Cook
Nexus Security