Re: [PATCH v4 00/14] Provide generic top-down mmap layout functions

[Alex Ghiti <alex@ghiti.fr>]

On 5/26/19 9:47 AM, Alexandre Ghiti wrote:
> This series introduces generic functions to make top-down mmap layout
> easily accessible to architectures, in particular riscv which was
> the initial goal of this series.
> The generic implementation was taken from arm64 and used successively
> by arm, mips and finally riscv.
>
> Note that in addition the series fixes 2 issues:
> - stack randomization was taken into account even if not necessary.
> - [1] fixed an issue with mmap base which did not take into account
>    randomization but did not report it to arm and mips, so by moving
>    arm64 into a generic library, this problem is now fixed for both
>    architectures.
>
> This work is an effort to factorize architecture functions to avoid
> code duplication and oversights as in [1].
>
> [1]: https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1429066.html
>
> Changes in v4:
>    - Make ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT select ARCH_HAS_ELF_RANDOMIZE
>      by default as suggested by Kees,
>    - ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT depends on MMU and defines the
>      functions needed by ARCH_HAS_ELF_RANDOMIZE => architectures that use
>      the generic mmap topdown functions cannot have ARCH_HAS_ELF_RANDOMIZE
>      selected without MMU, but I think it's ok since randomization without
>      MMU does not add much security anyway.
>    - There is no common API to determine if a process is 32b, so I came up with
>      !IS_ENABLED(CONFIG_64BIT) || is_compat_task() in [PATCH v4 12/14].
>    - Mention in the change log that x86 already takes care of not offseting mmap
>      base address if the task does not want randomization.
>    - Re-introduce a comment that should not have been removed.
>    - Add Reviewed/Acked-By from Paul, Christoph and Kees, thank you for that.
>    - I tried to minimize the changes from the commits in v3 in order to make
>      easier the review of the v4, the commits changed or added are:
>      - [PATCH v4 5/14]
>      - [PATCH v4 8/14]
>      - [PATCH v4 11/14]
>      - [PATCH v4 12/14]
>      - [PATCH v4 13/14]

Hi Paul,

Compared to the previous version you already acked, patches 11, 12 and 13
would need your feedback, do you have time to take a look at them ?

Hope I don't bother you,

Thanks,

Alex


>
> Changes in v3:
>    - Split into small patches to ease review as suggested by Christoph
>      Hellwig and Kees Cook
>    - Move help text of new config as a comment, as suggested by Christoph
>    - Make new config depend on MMU, as suggested by Christoph
>
> Changes in v2 as suggested by Christoph Hellwig:
>    - Preparatory patch that moves randomize_stack_top
>    - Fix duplicate config in riscv
>    - Align #if defined on next line => this gives rise to a checkpatch
>      warning. I found this pattern all around the tree, in the same proportion
>      as the previous pattern which was less pretty:
>      git grep -C 1 -n -P "^#if defined.+\|\|.*\\\\$"
>
> Alexandre Ghiti (14):
>    mm, fs: Move randomize_stack_top from fs to mm
>    arm64: Make use of is_compat_task instead of hardcoding this test
>    arm64: Consider stack randomization for mmap base only when necessary
>    arm64, mm: Move generic mmap layout functions to mm
>    arm64, mm: Make randomization selected by generic topdown mmap layout
>    arm: Properly account for stack randomization and stack guard gap
>    arm: Use STACK_TOP when computing mmap base address
>    arm: Use generic mmap top-down layout and brk randomization
>    mips: Properly account for stack randomization and stack guard gap
>    mips: Use STACK_TOP when computing mmap base address
>    mips: Adjust brk randomization offset to fit generic version
>    mips: Replace arch specific way to determine 32bit task with generic
>      version
>    mips: Use generic mmap top-down layout and brk randomization
>    riscv: Make mmap allocation top-down by default
>
>   arch/Kconfig                       |  11 +++
>   arch/arm/Kconfig                   |   2 +-
>   arch/arm/include/asm/processor.h   |   2 -
>   arch/arm/kernel/process.c          |   5 --
>   arch/arm/mm/mmap.c                 |  52 --------------
>   arch/arm64/Kconfig                 |   2 +-
>   arch/arm64/include/asm/processor.h |   2 -
>   arch/arm64/kernel/process.c        |   8 ---
>   arch/arm64/mm/mmap.c               |  72 -------------------
>   arch/mips/Kconfig                  |   2 +-
>   arch/mips/include/asm/processor.h  |   5 --
>   arch/mips/mm/mmap.c                |  84 ----------------------
>   arch/riscv/Kconfig                 |  11 +++
>   fs/binfmt_elf.c                    |  20 ------
>   include/linux/mm.h                 |   2 +
>   kernel/sysctl.c                    |   6 +-
>   mm/util.c                          | 107 ++++++++++++++++++++++++++++-
>   17 files changed, 137 insertions(+), 256 deletions(-)
>