[RFC,0/7] x86/module: use large ROX pages for text allocations

Message

Mike Rapoport April 11, 2024, 4:05 p.m. UTC

From: "Mike Rapoport (IBM)" <[e-mail]>

Hi,

These patches add support for using large ROX pages for allocations of
executable memory on x86.

They address Andy's comments [1] about having executable mappings for code
that was not completely formed.

The approach taken is to allocate ROX memory along with writable but not
executable memory and use the writable copy to perform relocations and
alternatives patching. After the module text gets into its final shape, the
contents of the writable memory is copied into the actual ROX location
using text poking.

The allocations of the ROX memory use vmalloc(VMAP_ALLOW_HUGE_MAP) to
allocate PMD aligned memory, fill that memory with invalid instructions and
in the end remap it as ROX. Portions of these large pages are handed out to
execmem_alloc() callers without any changes to the permissions. When the
memory is freed with execmem_free() it is invalidated again so that it
won't contain stale instructions.

The module memory allocation, x86 code dealing with relocations and
alternatives patching takes into account the existence of the two copies,
the writable memory and the ROX memory at the actual allocated virtual
address.

This is an early RFC, it is not well tested and there is a lot of room for
improvement. For example, the locking of execmem_cache can be made more
fine grained, freeing of PMD-sized pages from execmem_cache can be
implemented with a shrinker, the large pages can be removed from the direct
map when they are added to the cache and restored there when they are free
from the cache.

Still, I'd like to hear feedback on the approach in general before moving
forward with polishing the details.

The series applies on top of v4 of "jit/text allocator" [2] and also
available at git:

https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=execmem/v4%2bx86-rox

[1] https://lore.kernel.org/all/[e-mail]
[2] https://lore.kernel.org/linux-mm/[e-mail] 

Mike Rapoport (IBM) (6):
  asm-generic: introduce text-patching.h
  mm: vmalloc: don't account for number of nodes for HUGE_VMAP allocations
  module: prepare to handle ROX allocations for text
  x86/module: perpare module loading for ROX allocations of text
  execmem: add support for cache of large ROX pages
  x86/module: enable ROX caches for module text

Song Liu (1):
  ftrace: Add swap_func to ftrace_process_locs()

 arch/alpha/include/asm/Kbuild                 |   1 +
 arch/arc/include/asm/Kbuild                   |   1 +
 .../include/asm/{patch.h => text-patching.h}  |   0
 arch/arm/kernel/ftrace.c                      |   2 +-
 arch/arm/kernel/jump_label.c                  |   2 +-
 arch/arm/kernel/kgdb.c                        |   2 +-
 arch/arm/kernel/patch.c                       |   2 +-
 arch/arm/probes/kprobes/core.c                |   2 +-
 arch/arm/probes/kprobes/opt-arm.c             |   2 +-
 .../asm/{patching.h => text-patching.h}       |   0
 arch/arm64/kernel/ftrace.c                    |   2 +-
 arch/arm64/kernel/jump_label.c                |   2 +-
 arch/arm64/kernel/kgdb.c                      |   2 +-
 arch/arm64/kernel/patching.c                  |   2 +-
 arch/arm64/kernel/probes/kprobes.c            |   2 +-
 arch/arm64/kernel/traps.c                     |   2 +-
 arch/arm64/net/bpf_jit_comp.c                 |   2 +-
 arch/csky/include/asm/Kbuild                  |   1 +
 arch/hexagon/include/asm/Kbuild               |   1 +
 arch/loongarch/include/asm/Kbuild             |   1 +
 arch/m68k/include/asm/Kbuild                  |   1 +
 arch/microblaze/include/asm/Kbuild            |   1 +
 arch/mips/include/asm/Kbuild                  |   1 +
 arch/nios2/include/asm/Kbuild                 |   1 +
 arch/openrisc/include/asm/Kbuild              |   1 +
 .../include/asm/{patch.h => text-patching.h}  |   0
 arch/parisc/kernel/ftrace.c                   |   2 +-
 arch/parisc/kernel/jump_label.c               |   2 +-
 arch/parisc/kernel/kgdb.c                     |   2 +-
 arch/parisc/kernel/kprobes.c                  |   2 +-
 arch/parisc/kernel/patch.c                    |   2 +-
 arch/powerpc/include/asm/kprobes.h            |   2 +-
 .../asm/{code-patching.h => text-patching.h}  |   0
 arch/powerpc/kernel/crash_dump.c              |   2 +-
 arch/powerpc/kernel/epapr_paravirt.c          |   2 +-
 arch/powerpc/kernel/jump_label.c              |   2 +-
 arch/powerpc/kernel/kgdb.c                    |   2 +-
 arch/powerpc/kernel/kprobes.c                 |   2 +-
 arch/powerpc/kernel/module_32.c               |   2 +-
 arch/powerpc/kernel/module_64.c               |   2 +-
 arch/powerpc/kernel/optprobes.c               |   2 +-
 arch/powerpc/kernel/process.c                 |   2 +-
 arch/powerpc/kernel/security.c                |   2 +-
 arch/powerpc/kernel/setup_32.c                |   2 +-
 arch/powerpc/kernel/setup_64.c                |   2 +-
 arch/powerpc/kernel/static_call.c             |   2 +-
 arch/powerpc/kernel/trace/ftrace.c            |   2 +-
 arch/powerpc/kernel/trace/ftrace_64_pg.c      |   2 +-
 arch/powerpc/lib/code-patching.c              |   2 +-
 arch/powerpc/lib/feature-fixups.c             |   2 +-
 arch/powerpc/lib/test-code-patching.c         |   2 +-
 arch/powerpc/lib/test_emulate_step.c          |   2 +-
 arch/powerpc/mm/book3s32/mmu.c                |   2 +-
 arch/powerpc/mm/book3s64/hash_utils.c         |   2 +-
 arch/powerpc/mm/book3s64/slb.c                |   2 +-
 arch/powerpc/mm/kasan/init_32.c               |   2 +-
 arch/powerpc/mm/mem.c                         |   2 +-
 arch/powerpc/mm/nohash/44x.c                  |   2 +-
 arch/powerpc/mm/nohash/book3e_pgtable.c       |   2 +-
 arch/powerpc/mm/nohash/tlb.c                  |   2 +-
 arch/powerpc/net/bpf_jit_comp.c               |   2 +-
 arch/powerpc/perf/8xx-pmu.c                   |   2 +-
 arch/powerpc/perf/core-book3s.c               |   2 +-
 arch/powerpc/platforms/85xx/smp.c             |   2 +-
 arch/powerpc/platforms/86xx/mpc86xx_smp.c     |   2 +-
 arch/powerpc/platforms/cell/smp.c             |   2 +-
 arch/powerpc/platforms/powermac/smp.c         |   2 +-
 arch/powerpc/platforms/powernv/idle.c         |   2 +-
 arch/powerpc/platforms/powernv/smp.c          |   2 +-
 arch/powerpc/platforms/pseries/smp.c          |   2 +-
 arch/powerpc/xmon/xmon.c                      |   2 +-
 arch/riscv/errata/andes/errata.c              |   2 +-
 arch/riscv/errata/sifive/errata.c             |   2 +-
 arch/riscv/errata/thead/errata.c              |   2 +-
 .../include/asm/{patch.h => text-patching.h}  |   0
 arch/riscv/include/asm/uprobes.h              |   2 +-
 arch/riscv/kernel/alternative.c               |   2 +-
 arch/riscv/kernel/cpufeature.c                |   3 +-
 arch/riscv/kernel/ftrace.c                    |   2 +-
 arch/riscv/kernel/jump_label.c                |   2 +-
 arch/riscv/kernel/patch.c                     |   2 +-
 arch/riscv/kernel/probes/kprobes.c            |   2 +-
 arch/riscv/net/bpf_jit_comp64.c               |   2 +-
 arch/riscv/net/bpf_jit_core.c                 |   2 +-
 arch/sh/include/asm/Kbuild                    |   1 +
 arch/sparc/include/asm/Kbuild                 |   1 +
 arch/um/kernel/um_arch.c                      |  16 +-
 arch/x86/entry/vdso/vma.c                     |   3 +-
 arch/x86/include/asm/alternative.h            |  14 +-
 arch/x86/include/asm/text-patching.h          |   1 +
 arch/x86/kernel/alternative.c                 | 152 ++++++----
 arch/x86/kernel/ftrace.c                      |  41 ++-
 arch/x86/kernel/module.c                      |  17 +-
 arch/x86/mm/init.c                            |  29 +-
 arch/xtensa/include/asm/Kbuild                |   1 +
 include/asm-generic/text-patching.h           |   5 +
 include/linux/execmem.h                       |  25 ++
 include/linux/ftrace.h                        |   2 +
 include/linux/module.h                        |  11 +
 include/linux/text-patching.h                 |  15 +
 kernel/module/main.c                          |  70 ++++-
 kernel/module/strict_rwx.c                    |   3 +
 kernel/trace/ftrace.c                         |  13 +-
 mm/execmem.c                                  | 278 +++++++++++++++++-
 mm/vmalloc.c                                  |   9 +-
 105 files changed, 663 insertions(+), 193 deletions(-)
 rename arch/arm/include/asm/{patch.h => text-patching.h} (100%)
 rename arch/arm64/include/asm/{patching.h => text-patching.h} (100%)
 rename arch/parisc/include/asm/{patch.h => text-patching.h} (100%)
 rename arch/powerpc/include/asm/{code-patching.h => text-patching.h} (100%)
 rename arch/riscv/include/asm/{patch.h => text-patching.h} (100%)
 create mode 100644 include/asm-generic/text-patching.h
 create mode 100644 include/linux/text-patching.h