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    SubjectRe: [PATCH v3 2.6.39-rc1-tip 8/26] 8: uprobes: store/restore original instruction.
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    On Fri, 2011-04-01 at 20:03 +0530, Srikar Dronamraju wrote:

    > +static int __copy_insn(struct address_space *mapping, char *insn,
    > + unsigned long nbytes, unsigned long offset)
    > +{
    > + struct page *page;
    > + void *vaddr;
    > + unsigned long off1;
    > + loff_t idx;
    > +
    > + idx = offset >> PAGE_CACHE_SHIFT;
    > + off1 = offset &= ~PAGE_MASK;
    > + page = grab_cache_page(mapping, (unsigned long)idx);

    What if the page wasn't present due to being swapped out?

    > + if (!page)
    > + return -ENOMEM;
    > +
    > + vaddr = kmap_atomic(page, KM_USER0);
    > + memcpy(insn, vaddr + off1, nbytes);
    > + kunmap_atomic(vaddr, KM_USER0);
    > + unlock_page(page);
    > + page_cache_release(page);
    > + return 0;
    > +}
    > +
    > +static int copy_insn(struct uprobe *uprobe, unsigned long addr)
    > +{
    > + struct address_space *mapping;
    > + int bytes;
    > + unsigned long nbytes;
    > +
    > + addr &= ~PAGE_MASK;
    > + nbytes = PAGE_SIZE - addr;
    > + mapping = uprobe->inode->i_mapping;
    > +
    > + /* Instruction at end of binary; copy only available bytes */
    > + if (uprobe->offset + MAX_UINSN_BYTES > uprobe->inode->i_size)
    > + bytes = uprobe->inode->i_size - uprobe->offset;
    > + else
    > + bytes = MAX_UINSN_BYTES;
    > +
    > + /* Instruction at the page-boundary; copy bytes in second page */
    > + if (nbytes < bytes) {
    > + if (__copy_insn(mapping, uprobe->insn + nbytes,
    > + bytes - nbytes, uprobe->offset + nbytes))
    > + return -ENOMEM;
    > + bytes = nbytes;
    > + }
    > + return __copy_insn(mapping, uprobe->insn, bytes, uprobe->offset);
    > +}

    This all made me think why implement read_opcode() again.. I know its
    all slightly different, but still.

    > +static struct task_struct *uprobes_get_mm_owner(struct mm_struct *mm)
    > +{
    > + struct task_struct *tsk;
    > +
    > + rcu_read_lock();
    > + tsk = rcu_dereference(mm->owner);
    > + if (tsk)
    > + get_task_struct(tsk);
    > + rcu_read_unlock();
    > + return tsk;
    > +}

    Naming is somewhat inconsistent, most of your functions have the _uprobe
    postfix and now its a uprobes_ prefix all of a sudden.

    > static int install_uprobe(struct mm_struct *mm, struct uprobe *uprobe)
    > {
    > - int ret = 0;
    > + struct task_struct *tsk = uprobes_get_mm_owner(mm);
    > + int ret;
    >
    > - /*TODO: install breakpoint */
    > - if (!ret)
    > + if (!tsk) /* task is probably exiting; bail-out */
    > + return -ESRCH;
    > +
    > + if (!uprobe->copy) {
    > + ret = copy_insn(uprobe, mm->uprobes_vaddr);
    > + if (ret)
    > + goto put_return;
    > + if (is_bkpt_insn(uprobe->insn)) {
    > + print_insert_fail(tsk, mm->uprobes_vaddr,
    > + "breakpoint instruction already exists");
    > + ret = -EEXIST;
    > + goto put_return;
    > + }
    > + ret = analyze_insn(tsk, uprobe);
    > + if (ret) {
    > + print_insert_fail(tsk, mm->uprobes_vaddr,
    > + "instruction type cannot be probed");
    > + goto put_return;
    > + }

    If you want to expose this functionality to !root users printing stuff
    to dmesg like that isn't a good idea.

    > + uprobe->copy = 1;
    > + }
    > +
    > + ret = set_bkpt(tsk, uprobe, mm->uprobes_vaddr);
    > + if (ret < 0)
    > + print_insert_fail(tsk, mm->uprobes_vaddr,
    > + "failed to insert bkpt instruction");
    > + else
    > atomic_inc(&mm->uprobes_count);
    > +
    > +put_return:
    > + put_task_struct(tsk);
    > return ret;
    > }



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