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    SubjectRe: [PATCH v3 4/5] mm: Add a NO_INHERIT flag to the PR_SET_MDWE prctl
    On Fri, Aug 25, 2023 at 03:38:36PM -0700, Kees Cook wrote:
    > On Tue, Jul 04, 2023 at 05:36:28PM +0200, Florent Revest wrote:
    > > static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3,
    > > unsigned long arg4, unsigned long arg5)
    > > {
    > > + unsigned long current_bits;
    > > +
    > > if (arg3 || arg4 || arg5)
    > > return -EINVAL;
    > >
    > > - if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN))
    > > + if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT))
    > > + return -EINVAL;
    > > +
    > > + /* NO_INHERIT only makes sense with REFUSE_EXEC_GAIN */
    > > + if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN))
    > > return -EINVAL;
    > >
    > > + current_bits = get_current_mdwe();
    > > + if (current_bits && current_bits != bits)
    > > + return -EPERM; /* Cannot unset the flags */
    >
    > I was pondering why PR_MDWE_NO_INHERIT can't be unset, but I guess it
    > doesn't matter. Anything forked with have it off, and any process
    > wanting to launch stuff before locking down can just skip running the
    > prctl() until later.

    I had a similar doubt initially but then realised that the no-inherit
    mode won't be inherited and concluded it's ok.

    --
    Catalin

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