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SubjectRe: [PATCH v5 3.1.0-rc4-tip 18/26] uprobes: slot allocation.
On 09/20, Srikar Dronamraju wrote:
>
> - * valid_vma: Verify if the specified vma is an executable vma
> + * valid_vma: Verify if the specified vma is an executable vma,
> + * but not an XOL vma.
> * - Return 1 if the specified virtual address is in an
> - * executable vma.
> + * executable vma, but not in an XOL vma.
> */
> static bool valid_vma(struct vm_area_struct *vma)
> {
> + struct uprobes_xol_area *area = vma->vm_mm->uprobes_xol_area;
> +
> if (!vma->vm_file)
> return false;
>
> + if (area && (area->vaddr == vma->vm_start))
> + return false;

Could you explain why do we need this "but not an XOL vma" check?
xol_vma->vm_file is always NULL, no?

> +static struct uprobes_xol_area *xol_alloc_area(void)
> +{
> + struct uprobes_xol_area *area = NULL;
> +
> + area = kzalloc(sizeof(*area), GFP_KERNEL);
> + if (unlikely(!area))
> + return NULL;
> +
> + area->bitmap = kzalloc(BITS_TO_LONGS(UINSNS_PER_PAGE) * sizeof(long),
> + GFP_KERNEL);
> +
> + if (!area->bitmap)
> + goto fail;
> +
> + init_waitqueue_head(&area->wq);
> + spin_lock_init(&area->slot_lock);
> + if (!xol_add_vma(area) && !current->mm->uprobes_xol_area) {
> + task_lock(current);
> + if (!current->mm->uprobes_xol_area) {
> + current->mm->uprobes_xol_area = area;
> + task_unlock(current);
> + return area;
> + }
> + task_unlock(current);

But you can't rely on task_lock(), you can race with another thread
with the same ->mm. I guess you need mmap_sem or xchg().

> static int pre_ssout(struct uprobe *uprobe, struct pt_regs *regs,
> unsigned long vaddr)
> {
> - /* TODO: Yet to be implemented */
> + if (xol_get_insn_slot(uprobe, vaddr) && !pre_xol(uprobe, regs)) {
> + set_instruction_pointer(regs, current->utask->xol_vaddr);

set_instruction_pointer() looks unneded, pre_xol() has already changed
regs->ip.

Oleg.



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