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    SubjectRe: [PATCH 11/15] uprobes: move BUG_ON(UPROBE_SWBP_INSN_SIZE) from write_opcode() to install_breakpoint()

    >
    > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
    > index 14c71a2..b9c61bd 100644
    > --- a/kernel/events/uprobes.c
    > +++ b/kernel/events/uprobes.c
    > @@ -210,7 +210,6 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
    > void *vaddr_old, *vaddr_new;
    > struct vm_area_struct *vma;
    > struct uprobe *uprobe;
    > - unsigned long pgoff;
    > int ret;
    > retry:
    > /* Read the page with vaddr into memory */
    > @@ -251,11 +250,7 @@ retry:
    > vaddr_new = kmap_atomic(new_page);
    >
    > memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
    > -
    > - /* poke the new insn in, ASSUMES we don't cross page boundary */
    > - pgoff = (vaddr & ~PAGE_MASK);
    > - BUG_ON(pgoff + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
    > - memcpy(vaddr_new + pgoff, &opcode, UPROBE_SWBP_INSN_SIZE);
    > + memcpy(vaddr_new + (vaddr & ~PAGE_MASK), &opcode, UPROBE_SWBP_INSN_SIZE);
    >
    > kunmap_atomic(vaddr_new);
    > kunmap_atomic(vaddr_old);
    > @@ -699,6 +694,10 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
    > if (ret)
    > return ret;
    >
    > + /* write_opcode() assumes we don't cross page boundary */
    > + BUG_ON((uprobe->offset & ~PAGE_MASK) +
    > + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
    > +
    > uprobe->flags |= UPROBE_COPY_INSN;
    > }

    I am now thinking if we really need a BUG_ON? I am now thinking I should
    have had a check at the start in uprobe_register() and failed the request.

    Something like
    if ((offset & ~PAGE_MASK) + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE)
    return -EINVAL;
    --
    Thanks and Regards
    Srikar



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