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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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