On Tue, Oct 13, 2020 at 02:34:16AM +0100, Dmitry Safonov wrote:

Don't allow splitting of vm_special_mapping's.
It affects vdso/vvar areas. Uprobes have only one page in xol_area so
they aren't affected.

Those restrictions were enforced by checks in .mremap() callbacks.
Restrict resizing with generic .split() callback.

Signed-off-by: Dmitry Safonov <redacted>
---
 arch/arm/kernel/vdso.c    |  9 ---------
 arch/arm64/kernel/vdso.c  | 41 +++------------------------------------
 arch/mips/vdso/genvdso.c  |  4 ----
 arch/s390/kernel/vdso.c   | 11 +----------
 arch/x86/entry/vdso/vma.c | 17 ----------------
 mm/mmap.c                 | 12 ++++++++++++
 6 files changed, 16 insertions(+), 78 deletions(-)

For arm64:

Acked-by: Will Deacon <will@kernel.org>

Will