On Wed, Jul 13, 2022 at 1:13 AM Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> Add a couple of arch_prctl() handles:
>
> - ARCH_ENABLE_TAGGED_ADDR enabled LAM. The argument is required number
> of tag bits. It is rounded up to the nearest LAM mode that can
> provide it. For now only LAM_U57 is supported, with 6 tag bits.
>
> - ARCH_GET_UNTAG_MASK returns untag mask. It can indicates where tag
> bits located in the address.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> arch/x86/include/uapi/asm/prctl.h | 3 ++
> arch/x86/kernel/process_64.c | 60 ++++++++++++++++++++++++++++++-
> 2 files changed, 62 insertions(+), 1 deletion(-)
> +
> +static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
> +{
> + int ret = 0;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_LAM))
> + return -ENODEV;
Hm, I used to think ENODEV is specific to devices, and -EINVAL is more
appropriate here.
On the other hand, e.g. prctl(PR_SET_SPECULATION_CTRL) can also return ENODEV...
> long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
> {
> int ret = 0;
> @@ -829,7 +883,11 @@ 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(task->mm->context.untag_mask,
> + (unsigned long __user *)arg2);
Can we have ARCH_GET_UNTAG_MASK return the same error value (ENODEV or
EINVAL) as ARCH_ENABLE_TAGGED_ADDR in the case the host doesn't
support LAM?
After all, the mask does not make much sense in this case.
> + case ARCH_ENABLE_TAGGED_ADDR:
> + return prctl_enable_tagged_addr(task->mm, arg2);
> default:
> ret = -EINVAL;
> break;
> --
> 2.35.1
>
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
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