Re: [PATCH 09/10] mm: Prevent madvise from changing shadow stack

[Nadav Amit]

Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:

> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> ---
> mm/madvise.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 4d3c922ea1a1..2a6988badd6b 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -839,6 +839,14 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> 	if (vma && start > vma->vm_start)
> 		prev = vma;
> 
> +	/*
> +	 * Don't do anything on shadow stack.
> +	 */
> +	if (vma->vm_flags & VM_SHSTK) {
> +		error = -EINVAL;
> +		goto out_no_plug;
> +	}
> +
> 	blk_start_plug(&plug);
> 	for (;;) {
> 		/* Still start < end. */

What happens if the madvise() revolves multiple VMAs, the first one is not
VM_SHSTK, but the another one is? Shouldnât the test be done inside the
loop, potentially in madvise_vma() ?