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SubjectRe: [PATCH 09/10] mm: Prevent madvise from changing shadow stack
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Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:

> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> ---
> 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? Shouldn’t the test be done inside the
loop, potentially in madvise_vma() ?

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