[kernel-hardening] [PATCH v6 00/11] arm64: mmu: avoid W+X mappings and re-enable PTE_CONT for kernel

Ard Biesheuvel
2017-03-09T20:51:58Z

Having memory that is writable and executable at the same time is a
security hazard, and so we tend to avoid those when we can. However,
at boot time, we keep .text mapped writable during the entire init
phase, and the init region itself is mapped rwx as well.

Let's improve the situation by:
- making the alternatives patching use the linear mapping
- splitting the init region into separate text and data regions

This removes all RWX mappings except the really early one created
in head.S (which we could perhaps fix in the future as well). Due to
these changes, it is also possible to make another attempt at re-enabling
the use of contiguous mappings at the PMD and PTE levels.

Changes since v5:
- add patch to remove pointless mapping/unmapping of translation table pages
when the higher level table entry pointing to it is created
- fix unitialized flags var in #9
- allow contiguous ranges for mappings created via create_pgd_mapping (ie., EFI)
- refactor pud/pmd/pte recursion logic so we don't iterate over pmds and ptes
at two separate levels concurrently (ie., cont and non-cont)
- use macros rather than static inlines for pmd_/pte_cont_addr_end()
- add Mark's R-b to #6 - #9

Changes since v4:
- the PTE_CONT patch has now spawned four more preparatory patches that clean
up some of the page table creation code before reintroducing the contiguous
attribute management
- add Mark's R-b to #4 and #5

Changes since v3:
- use linear alias only when patching the core kernel, and not for modules
- add patch to reintroduce the use of PTE_CONT for kernel mappings, except
for regions that are remapped read-only later on (i.e, .rodata and the
linear alias of .text+.rodata)

Changes since v2:
- ensure that text mappings remain writable under rodata=off
- rename create_mapping_late() to update_mapping_prot()
- clarify commit log of #2
- add acks

Ard Biesheuvel (11):
arm: kvm: move kvm_vgic_global_state out of .text section
arm64: mmu: move TLB maintenance from callers to create_mapping_late()
arm64: alternatives: apply boot time fixups via the linear mapping
arm64: mmu: map .text as read-only from the outset
arm64: mmu: apply strict permissions to .init.text and .init.data
arm64/mmu: align alloc_init_pte prototype with pmd/pud versions
arm64/mmu: ignore debug_pagealloc for kernel segments
arm64/mmu: add contiguous bit to sanity bug check
arm64/mmu: replace 'page_mappings_only' parameter with flags argument
arm64/mm: remove pointless map/unmap sequences when creating page
tables
arm64: mm: set the contiguous bit for kernel mappings where
appropriate

arch/arm64/include/asm/mmu.h | 1 +
arch/arm64/include/asm/pgtable.h | 10 +
arch/arm64/include/asm/sections.h | 2 +
arch/arm64/kernel/alternative.c | 11 +-
arch/arm64/kernel/smp.c | 1 +
arch/arm64/kernel/vmlinux.lds.S | 25 +-
arch/arm64/mm/mmu.c | 246 ++++++++++++++------
virt/kvm/arm/vgic/vgic.c | 4 +-
8 files changed, 208 insertions(+), 92 deletions(-)

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2.7.4