Re: [PATCH v4 0/3] x86/64/KASLR: Change kernel mapping size to 1G unconditionally

[Kees Cook]

On Thu, Feb 2, 2017 at 4:54 AM, Baoquan He <bhe@xxxxxxxxxx> wrote:
> This is v4 post.
>
> In the previous 3 versions I tried to detect and determine kernel image
> mapping size at runtime for x86_64. With this the inconsistency between
> KASLR code is not compiled in by disabling CONFIG_RANDOMIZE_BASE and
> KASLR code is compiled in but add 'nokaslr' kernel option can be fixed.
>
> When review v3 Boris suggested we should change kernel mapping size to
> 1G directly, but not an option. Kees explained he made kernel mapping
> size as an option mainly because he woried about kernel module space.
> He said it wasn't clear to him at the time if enough space remained for
> modules in all use-cases. Then Boris pointed out that practically kaslr
> will be enabled on the majority of the systems anyway, and the reduction
> of kernel modules mapping space has been there for a while now, if so we
> probably whould've heard complaints already. Kees agreed.
>
> So in this version of post change kernel mapping size of x86 64 to 1G
> as Boris suggested. Then the inconsistency will naturally disappear.
>
> And I still keep patch 1/3 which introduces the new constant
> KERNEL_MAPPING_SIZE. And let KERNEL_IMAGE_SIZE stay for restricting kernel
> image size during linking stage.
>
>
> v3->v4:
>     Change kernel mapping size to 1G unconditionally as Boris suggested.

This looks good to me.

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

>
> v2->v3:
>     Boris pointed out patch log is not good for reviewing and understanding.
>     So split the old patch 2/2 into 2 parts and rewrite the patch log,
>     patch 2/3 is introducing the new constant KERNEL_MAPPING_SIZE which
>     differs from the old KERNEL_IMAGE_SIZE, patch 3/3 gets the kernel mapping
>     size at runtime.
>
> v1->v2:
>     Kbuild test threw build warning because of code bug.
>
>
> Baoquan He (3):
>   x86: Introduce a new constant KERNEL_MAPPING_SIZE
>   x86/64/KASLR: Change kernel mapping size to 1G unconditionally
>   x86/64/doc: Update the ranges of kernel text and modules mapping
>
>  Documentation/x86/x86_64/mm.txt         |  4 ++--
>  arch/x86/boot/compressed/kaslr.c        | 10 +++++-----
>  arch/x86/include/asm/page_32_types.h    |  6 ++++++
>  arch/x86/include/asm/page_64_types.h    | 17 ++++++++---------
>  arch/x86/include/asm/pgtable_64_types.h |  2 +-
>  arch/x86/kernel/head64.c                |  4 ++--
>  arch/x86/kernel/head_64.S               | 12 +++++-------
>  arch/x86/kernel/machine_kexec_64.c      |  2 +-
>  arch/x86/mm/init_64.c                   |  2 +-
>  arch/x86/mm/physaddr.c                  |  6 +++---
>  10 files changed, 34 insertions(+), 31 deletions(-)
>
> --
> 2.5.5
>



-- 
Kees Cook
Pixel Security