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    SubjectRe: [RFC PATCH v2 15/27] mm/mprotect: Prevent mprotect from changing shadow stack
    On Tue, Jul 10, 2018 at 04:10:08PM -0700, Dave Hansen wrote:
    > On 07/10/2018 03:26 PM, Yu-cheng Yu wrote:
    > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
    >
    > This still needs a changelog, even if you think it's simple.
    > > --- a/mm/mprotect.c
    > > +++ b/mm/mprotect.c
    > > @@ -446,6 +446,15 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
    > > error = -ENOMEM;
    > > if (!vma)
    > > goto out;
    > > +
    > > + /*
    > > + * Do not allow changing shadow stack memory.
    > > + */
    > > + if (vma->vm_flags & VM_SHSTK) {
    > > + error = -EINVAL;
    > > + goto out;
    > > + }
    > > +
    >
    > I think this is a _bit_ draconian. Why shouldn't we be able to use
    > protection keys with a shadow stack? Or, set it to PROT_NONE?

    Right, and then there's also madvise() and some of the other accessors.

    Why do we need to disallow this? AFAICT the worst that can happen is
    that a process wrecks itself, so what?

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