[PATCH 0/3] x86/dumpstack: Inline copy_from_user_nmi()

[Kees Cook <keescook@chromium.org>]

Hi,

This fixes a find_vmap_area() deadlock. The main fix is patch 2, repeated here:

    The check_object_size() helper under CONFIG_HARDENED_USERCOPY is
    designed to skip any checks where the length is known at compile time as
    a reasonable heuristic to avoid "likely known-good" cases. However, it can
    only do this when the copy_*_user() helpers are, themselves, inline too.

    Using find_vmap_area() requires taking a spinlock. The check_object_size()
    helper can call find_vmap_area() when the destination is in vmap memory.
    If show_regs() is called in interrupt context, it will attempt a call to
    copy_from_user_nmi(), which may call check_object_size() and then
    find_vmap_area(). If something in normal context happens to be in the
    middle of calling find_vmap_area() (with the spinlock held), the interrupt
    handler will hang forever.

    The copy_from_user_nmi() call is actually being called with a fixed-size
    length, so check_object_size() should never have been called in the
    first place. In order for check_object_size() to see that the length is
    a fixed size, inline copy_from_user_nmi(), as already done with all the
    other uaccess helpers.

    Reported-by: Yu Zhao <yuzhao@google.com>
    Link: https://lore.kernel.org/all/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b3EQ@mail.gmail.com
    Reported-by: dev@der-flo.net

Patch 1 is a refactor for patch 2, and patch 3 should make sure we avoid
future deadlocks.

Thanks,

-Kees


Kees Cook (3):
  x86/uaccess: Move nmi_uaccess_okay() into uaccess.h
  x86/dumpstack: Inline copy_from_user_nmi()
  usercopy: Add find_vmap_area_try() to avoid deadlocks

 arch/x86/events/core.c          |  1 -
 arch/x86/include/asm/tlbflush.h |  3 --
 arch/x86/include/asm/uaccess.h  |  5 ++--
 arch/x86/kernel/dumpstack.c     |  4 +--
 arch/x86/lib/Makefile           |  2 +-
 arch/x86/lib/usercopy.c         | 52 ---------------------------------
 include/asm-generic/tlb.h       |  9 ------
 include/linux/uaccess.h         | 50 +++++++++++++++++++++++++++++++
 include/linux/vmalloc.h         |  1 +
 kernel/trace/bpf_trace.c        |  2 --
 mm/usercopy.c                   | 11 ++++++-
 mm/vmalloc.c                    | 11 +++++++
 12 files changed, 78 insertions(+), 73 deletions(-)
 delete mode 100644 arch/x86/lib/usercopy.c

-- 
2.34.1