[PATCH 0/4] mm: Avoid sharing high VMA flag bits

[Florent Revest]

While staring at include/linux/mm.h, I was wondering why VM_UFFD_MINOR and
VM_SHADOW_STACK share the same bit on arm64. I think I gained enough confidence
now to call it a bug.

The first patch of this series is a straightforward attempt at fixing this
specific bug by changing the bit used by VM_UFFD_MINOR. I cc-ed stable on that
one and I expect it to not be all too controversial.

The rest of the series however is a more zealous refactoring and likely to be
more contentious... :) Since this bug looks like a near miss which could have
been quite severe in terms of security, I think it's worth trying to simplify
the high VMA flag bits code. I tried to consolidate around the current usage of
VM_HIGH_ARCH_* macros but I'm not sure if this is the preferred approach here. I
really don't feel strongly about those refactorings so this is more of a
platform for discussion for people with more mm background, I'll be more than
happy to respin a v2!

This series applies on v6.15-rc5.

Florent Revest (4):
  mm: fix VM_UFFD_MINOR == VM_SHADOW_STACK on USERFAULTFD=y &&
    ARM64_GCS=y
  mm: remove CONFIG_ARCH_USES_HIGH_VMA_FLAGS
  mm: use VM_HIGH_ARCH_* macros consistently
  mm: consolidate VM_HIGH_ARCH_* macros into parametric macros

 arch/arm64/Kconfig   |  3 ---
 arch/powerpc/Kconfig |  1 -
 arch/x86/Kconfig     |  2 --
 include/linux/mm.h   | 49 +++++++++++++++-----------------------------
 mm/Kconfig           |  2 --
 5 files changed, 17 insertions(+), 40 deletions(-)

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2.49.0.967.g6a0df3ecc3-goog