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    Subject[PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder
    Date
    Convert arch_within_stack_frames() to use the new unwinder.

    This also changes some existing behavior:

    - Skip checking of pt_regs frames.
    - Warn if it can't reach the grandparent's stack frame.
    - Warn if it doesn't unwind to the end of the stack.

    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    ---
    arch/x86/lib/usercopy.c | 44 ++++++++++++++++++++++++++++----------------
    1 file changed, 28 insertions(+), 16 deletions(-)

    diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
    index 2492fa7..8fe0a9c 100644
    --- a/arch/x86/lib/usercopy.c
    +++ b/arch/x86/lib/usercopy.c
    @@ -50,30 +50,42 @@ int arch_within_stack_frames(const void * const stack,
    const void * const stackend,
    const void *obj, unsigned long len)
    {
    - const void *frame = NULL;
    - const void *oldframe;
    + struct unwind_state state;
    + const void *frame, *frame_end;
    +
    + /*
    + * Start at the end of our grandparent's frame (beginning of
    + * great-grandparent's frame).
    + */
    + unwind_start(&state, current, NULL, NULL);
    + if (WARN_ON_ONCE(!unwind_next_frame(&state) ||
    + !unwind_next_frame(&state)))
    + return 0;
    + frame = unwind_get_stack_ptr(&state);

    - oldframe = __builtin_frame_address(2);
    - if (oldframe)
    - frame = __builtin_frame_address(3);
    /*
    * low ----------------------------------------------> high
    * [saved bp][saved ip][args][local vars][saved bp][saved ip]
    * ^----------------^
    * allow copies only within here
    */
    - while (stack <= frame && frame < stackend) {
    - /*
    - * If obj + len extends past the last frame, this
    - * check won't pass and the next frame will be 0,
    - * causing us to bail out and correctly report
    - * the copy as invalid.
    - */
    - if (obj + len <= frame)
    - return obj >= oldframe + 2 * sizeof(void *) ? 1 : -1;
    - oldframe = frame;
    - frame = *(const void * const *)frame;
    + frame += 2*sizeof(long);
    +
    + while (unwind_next_frame(&state)) {
    + frame_end = unwind_get_stack_ptr(&state);
    +
    + /* skip checking of pt_regs frames */
    + if (!unwind_get_entry_regs(&state) &&
    + obj >= frame && obj + len <= frame_end)
    + return 1;
    +
    + frame = frame_end + 2*sizeof(long);
    }
    +
    + /* make sure the unwinder reached the end of the task stack */
    + if (WARN_ON_ONCE(frame != (void *)task_pt_regs(current)))
    + return 0;
    +
    return -1;
    }
    #endif /* CONFIG_HARDENED_USERCOPY && CONFIG_FRAME_POINTER */
    --
    2.7.4
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