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

From: Alexandre Ghiti
Date: Wed Jul 24 2019 - 01:59:09 EST

Hi Andrew,

This is simply a rebase on top of next-20190719, where I added various
Acked/Reviewed-by from Kees and Catalin and a note on commit 08/14 suggested
by Kees regarding the removal of STACK_RND_MASK that is safe doing.

I would have appreciated a feedback from a mips maintainer but failed to get
it: can you consider this series for inclusion anyway ? Mips parts have been
reviewed-by Kees.


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

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:
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]

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
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(-)