[v5,00/23] x86: text_poke() fixes and executable lockdowns

Message

Nadav Amit April 26, 2019, 12:11 a.m. UTC

Yet another version, per PeterZ request, addressing the latest feedback.

This patchset improves several overlapping issues around stale TLB
entries and W^X violations. It is combined from "x86/alternative:
text_poke() enhancements v7" [1] and "Don't leave executable TLB entries
to freed pages v2" [2] patchsets that were conflicting.

The related issues that this fixes:
1. Fixmap PTEs that are used for patching are available for access from
  other cores and might be exploited. They are not even flushed from
  the TLB in remote cores, so the risk is even higher. Address this
  issue by introducing a temporary mm that is only used during
  patching. Unfortunately, due to init ordering, fixmap is still used
  during boot-time patching. Future patches can eliminate the need for
  it.
2. Missing lockdep assertion to ensure text_mutex is taken. It is
  actually not always taken, so fix the instances that were found not
  to take the lock (although they should be safe even without taking
  the lock).
3. Module_alloc returning memory that is RWX until a module is finished
  loading.
4. Sometimes when memory is freed via the module subsystem, an
  executable permissioned TLB entry can remain to a freed page. If the
  page is re-used to back an address that will receive data from
  userspace, it can result in user data being mapped as executable in
  the kernel. The root of this behavior is vfree lazily flushing the
  TLB, but not lazily freeing the underlying pages.


Changes v4 to v5:
- Change temporary state variable name [Borislav]
- Commit log and comment fixes [Borislav]

Changes v3 to v4:
- Remove the size parameter from tramp_free() [Steven]
- Remove caching of hw_breakpoint_active() [Sean]
- Prevent the use of bpf_probe_write_user() while using temporary mm [Jann]
- Fix build issues on other archs

Changes v2 to v3:
- Fix commit messages and comments [Boris]
- Rename VM_HAS_SPECIAL_PERMS [Boris]
- Remove unnecessary local variables [Boris]
- Rename set_alias_*() functions [Boris, Andy]
- Save/restore DR registers when using temporary mm
- Move line deletion from patch 10 to patch 17

Changes v1 to v2:
- Adding "Reviewed-by tag" [Masami]
- Comment instead of code to warn against module removal while
  patching [Masami]
- Avoiding open-coded TLB flush [Andy]
- Remove "This patch" [Borislav Petkov]
- Not set global bit during text poking [Andy, hpa]
- Add Ack from [Pavel Machek]
- Split patch 16 "Plug in new special vfree flag" into 4 patches (16-19)
  to make it easier to review. There were no code changes.

The changes from "Don't leave executable TLB entries to freed pages
v2" to v1:
- Add support for case of hibernate trying to save an unmapped page
  on the directmap. (Ard Biesheuvel)
- No week arch breakout for vfree-ing special memory (Andy Lutomirski)
- Avoid changing deferred free code by moving modules init free to work
  queue (Andy Lutomirski)
- Plug in new flag for kprobes and ftrace
- More arch generic names for set_pages functions (Ard Biesheuvel)
- Fix for TLB not always flushing the directmap (Nadav Amit)

Changes from "x86/alternative: text_poke() enhancements v7" to v1
- Fix build failure on CONFIG_RANDOMIZE_BASE=n (Rick)
- Remove text_poke usage from ftrace (Nadav)

[1] https://lkml.org/lkml/2018/12/5/200
[2] https://lkml.org/lkml/2018/12/11/1571


Andy Lutomirski (1):
  x86/mm: Introduce temporary mm structs

Nadav Amit (15):
  Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"
  x86/jump_label: Use text_poke_early() during early init
  x86/mm: Save debug registers when loading a temporary mm
  fork: Provide a function for copying init_mm
  x86/alternative: Initialize temporary mm for patching
  x86/alternative: Use temporary mm for text poking
  x86/kgdb: Avoid redundant comparison of patched code
  x86/ftrace: Set trampoline pages as executable
  x86/kprobes: Set instruction page as executable
  x86/module: Avoid breaking W^X while loading modules
  x86/jump-label: Remove support for custom poker
  x86/alternative: Remove the return value of text_poke_*()
  x86/alternative: Comment about module removal races
  mm/tlb: Provide default nmi_uaccess_okay()
  bpf: Fail bpf_probe_write_user() while mm is switched

Rick Edgecombe (7):
  x86/mm/cpa: Add set_direct_map_ functions
  mm: Make hibernate handle unmapped pages
  vmalloc: Add flag for free of special permsissions
  modules: Use vmalloc special flag
  bpf: Use vmalloc special flag
  x86/ftrace: Use vmalloc special flag
  x86/kprobes: Use vmalloc special flag

 arch/Kconfig                         |   4 +
 arch/x86/Kconfig                     |   1 +
 arch/x86/include/asm/fixmap.h        |   2 -
 arch/x86/include/asm/mmu_context.h   |  56 ++++++++
 arch/x86/include/asm/pgtable.h       |   3 +
 arch/x86/include/asm/set_memory.h    |   3 +
 arch/x86/include/asm/text-patching.h |   7 +-
 arch/x86/include/asm/tlbflush.h      |   2 +
 arch/x86/kernel/alternative.c        | 201 ++++++++++++++++++++-------
 arch/x86/kernel/ftrace.c             |  22 +--
 arch/x86/kernel/jump_label.c         |  21 ++-
 arch/x86/kernel/kgdb.c               |  25 +---
 arch/x86/kernel/kprobes/core.c       |  19 ++-
 arch/x86/kernel/module.c             |   2 +-
 arch/x86/mm/init_64.c                |  36 +++++
 arch/x86/mm/pageattr.c               |  16 ++-
 arch/x86/xen/mmu_pv.c                |   2 -
 include/asm-generic/tlb.h            |   9 ++
 include/linux/filter.h               |  18 +--
 include/linux/mm.h                   |  18 +--
 include/linux/sched/task.h           |   1 +
 include/linux/set_memory.h           |  11 ++
 include/linux/vmalloc.h              |  15 ++
 init/main.c                          |   3 +
 kernel/bpf/core.c                    |   1 -
 kernel/fork.c                        |  24 +++-
 kernel/module.c                      |  82 ++++++-----
 kernel/power/snapshot.c              |   5 +-
 kernel/trace/bpf_trace.c             |   8 ++
 mm/page_alloc.c                      |   7 +-
 mm/vmalloc.c                         | 113 ++++++++++++---
 31 files changed, 542 insertions(+), 195 deletions(-)

Comments

Peter Zijlstra April 26, 2019, 12:36 p.m. UTC | #1

On Thu, Apr 25, 2019 at 05:11:20PM -0700, Nadav Amit wrote:
> Yet another version, per PeterZ request, addressing the latest feedback.
> 

Well, I would've been OK with just an updated to the one patch, but
thanks. Let me see if I can get all that to apply :-)