Re: [PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR

Edgecombe, Rick P
2022-06-10T15:25:10Z

On Fri, 2022-06-10 at 17:35 +0300, Kirill A. Shutemov wrote:
> +static int prctl_enable_tagged_addr(unsigned long nr_bits)
> +{
> + struct mm_struct *mm = current->mm;

do_arch_prctl_64() can be called via ptrace. I think you need to
operate on the mm of 'task', or just block the operation if task !=
current.

> +
> + /* Already enabled? */
> + if (mm->context.lam_cr3_mask)
> + return -EBUSY;
> +
> + /* LAM has to be enabled before spawning threads */
> + if (get_nr_threads(current) > 1)
> + return -EBUSY;
> +
> + if (!nr_bits) {
> + return -EINVAL;
> + } else if (nr_bits <= 6) {
> + mm->context.lam_cr3_mask = X86_CR3_LAM_U57;
> + mm->context.untag_mask = ~GENMASK(62, 57);
> + } else {
> + return -EINVAL;
> + }
> +
> + /* Update CR3 to get LAM active */
> + switch_mm(current->mm, current->mm, current);
> + return 0;
> +}
> +
> long do_arch_prctl_64(struct task_struct *task, int option, unsigned
> long arg2)
> {
> int ret = 0;
> @@ -829,7 +855,11 @@ long do_arch_prctl_64(struct task_struct *task,
> int option, unsigned long arg2)
> case ARCH_MAP_VDSO_64:
> return prctl_map_vdso(&vdso_image_64, arg2);
> #endif
> -
> + case ARCH_GET_UNTAG_MASK:
> + return put_user(current->mm->context.untag_mask,
> + (unsigned long __user *)arg2);
> + case ARCH_ENABLE_TAGGED_ADDR:
> + return prctl_enable_tagged_addr(arg2);
> default:
> ret = -EINVAL;
> break;