Messages in this thread | | | Date | Tue, 15 Mar 2011 14:22:09 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH v2 2.6.38-rc8-tip 3/20] 3: uprobes: Breakground page replacement. |
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On Mon, 14 Mar 2011, Srikar Dronamraju wrote: > +/* > + * Called with tsk->mm->mmap_sem held (either for read or write and > + * with a reference to tsk->mm
Hmm, why is holding it for read sufficient? . > + */ > +static int write_opcode(struct task_struct *tsk, struct uprobe * uprobe, > + unsigned long vaddr, uprobe_opcode_t opcode) > +{ > + struct page *old_page, *new_page; > + void *vaddr_old, *vaddr_new; > + struct vm_area_struct *vma; > + spinlock_t *ptl; > + pte_t *orig_pte; > + unsigned long addr; > + int ret = -EINVAL;
That initialization is pointless.
> + /* Read the page with vaddr into memory */ > + ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 1, 1, &old_page, &vma); > + if (ret <= 0) > + return -EINVAL; > + ret = -EINVAL; > + > + /* > + * check if the page we are interested is read-only mapped > + * Since we are interested in text pages, Our pages of interest > + * should be mapped read-only. > + */ > + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) == > + (VM_READ|VM_EXEC)) > + goto put_out;
IIRC then text pages are (VM_READ|VM_EXEC)
> + /* Allocate a page */ > + new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr); > + if (!new_page) { > + ret = -ENOMEM; > + goto put_out; > + } > + > + /* > + * lock page will serialize against do_wp_page()'s > + * PageAnon() handling > + */ > + lock_page(old_page); > + /* copy the page now that we've got it stable */ > + vaddr_old = kmap_atomic(old_page, KM_USER0); > + vaddr_new = kmap_atomic(new_page, KM_USER1); > + > + memcpy(vaddr_new, vaddr_old, PAGE_SIZE); > + /* poke the new insn in, ASSUMES we don't cross page boundary */
And what makes sure that we don't ?
> + addr = vaddr; > + vaddr &= ~PAGE_MASK; > + memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz); > + > + kunmap_atomic(vaddr_new, KM_USER1); > + kunmap_atomic(vaddr_old, KM_USER0); > + > + orig_pte = page_check_address(old_page, tsk->mm, addr, &ptl, 0); > + if (!orig_pte) > + goto unlock_out; > + pte_unmap_unlock(orig_pte, ptl); > + > + lock_page(new_page); > + if (!anon_vma_prepare(vma))
Why don't you get the error code of anon_vma_prepare()?
> + /* flip pages, do_wp_page() will fail pte_same() and bail */
-ENOPARSE
> + ret = replace_page(vma, old_page, new_page, *orig_pte); > + > + unlock_page(new_page); > + if (ret != 0) > + page_cache_release(new_page); > +unlock_out: > + unlock_page(old_page); > + > +put_out: > + put_page(old_page); /* we did a get_page in the beginning */ > + return ret; > +} > + > +/** > + * read_opcode - read the opcode at a given virtual address. > + * @tsk: the probed task. > + * @vaddr: the virtual address to store the opcode. > + * @opcode: location to store the read opcode. > + * > + * For task @tsk, read the opcode at @vaddr and store it in @opcode. > + * Return 0 (success) or a negative errno.
Wants to called with mmap_sem held as well, right ?
> + */ > +int __weak read_opcode(struct task_struct *tsk, unsigned long vaddr, > + uprobe_opcode_t *opcode) > +{ > + struct vm_area_struct *vma; > + struct page *page; > + void *vaddr_new; > + int ret; > + > + ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 0, 0, &page, &vma); > + if (ret <= 0) > + return -EFAULT; > + ret = -EFAULT; > + > + /* > + * check if the page we are interested is read-only mapped > + * Since we are interested in text pages, Our pages of interest > + * should be mapped read-only. > + */ > + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) == > + (VM_READ|VM_EXEC)) > + goto put_out;
Same as above
> + lock_page(page); > + vaddr_new = kmap_atomic(page, KM_USER0); > + vaddr &= ~PAGE_MASK; > + memcpy(&opcode, vaddr_new + vaddr, uprobe_opcode_sz); > + kunmap_atomic(vaddr_new, KM_USER0); > + unlock_page(page); > + ret = uprobe_opcode_sz;
ret = 0 ?? At least, that's what the comment above says.
> + > +put_out: > + put_page(page); /* we did a get_page in the beginning */ > + return ret; > +} > +
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