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    SubjectRe: [PATCH 2/3] arm64: signal: sigreturn() and rt_sigreturn() sometime returns the wrong signals
    Liam Howlett <liam.howlett@oracle.com> writes:

    > This is way out of scope for what I'm doing. I'm trying to fix a call
    > to the wrong mm API. I was trying to clean up any obvious errors in
    > calling functions which were exposed by fixing that error. If you want
    > this fixed differently, then please go ahead and tackle the problems you
    > see.

    I was asked by the arm maintainers to describe what the code should be
    doing here. I hope I have done that.

    What is very interesting is that the code in __do_page_fault does not
    use find_vma_intersection it uses find_vma. Which suggests that
    find_vma_intersection may not be the proper mm api.

    The logic is:

    From __do_page_fault:
    struct vm_area_struct *vma = find_vma(mm, addr);

    if (unlikely(!vma))
    return VM_FAULT_BADMAP;

    /*
    * Ok, we have a good vm_area for this memory access, so we can handle
    * it.
    */
    if (unlikely(vma->vm_start > addr)) {
    if (!(vma->vm_flags & VM_GROWSDOWN))
    return VM_FAULT_BADMAP;
    if (expand_stack(vma, addr))
    return VM_FAULT_BADMAP;
    }

    /*
    * Check that the permissions on the VMA allow for the fault which
    * occurred.
    */
    if (!(vma->vm_flags & vm_flags))
    return VM_FAULT_BADACCESS;

    From do_page_fault:

    arm64_force_sig_fault(SIGSEGV,
    fault == VM_FAULT_BADACCESS ? SEGV_ACCERR : SEGV_MAPERR,
    far, inf->name);


    Hmm. If the expand_stack step is skipped. Does is the logic equivalent
    to find_vma_intersection?

    static inline struct vm_area_struct *find_vma_intersection(
    struct mm_struct * mm,
    unsigned long start_addr,
    unsigned long end_addr)
    {
    struct vm_area_struct * vma = find_vma(mm,start_addr);

    if (vma && end_addr <= vma->vm_start)
    vma = NULL;
    return vma;
    }

    Yes. It does look that way. VM_FAULT_BADMAP is returned when a vma
    covering the specified address is not found. And VM_FAULT_BADACCESS is
    returned when there is a vma and there is a permission problem.

    There are also two SIGBUS cases that arm64_notify_segfault does not
    handle.

    So it appears changing arm64_notify_segfault to use
    find_vma_intersection instead of find_vma would be a correct but
    incomplete fix.

    I don't see a point in changing sigerturn or rt_sigreturn.

    Eric

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