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

[Alex Ghiti]

On 6/13/19 1:29 AM, Alex Ghiti wrote:
> 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@xxxxxxxxxxxxxxx/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

Hi Paul,

Would you have time to give your feedback on patches 11, 12 and 13 ?

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(-)
>
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