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    SubjectRe: Compat 32-bit syscall entry from 64-bit task!? [was: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]
    On Wed, Jan 18, 2012 at 7:04 AM, Eric Paris <eparis@redhat.com> wrote:
    >
    > Gratuitous SELinux for the win e-mail!  (Feel free to delete now)  We
    > typically, for all confined domains, do not allow mapping anonymous
    > memory both W and X.  Actually you can't even map it W and then map it
    > X...

    That doesn't help.

    Anonymous memory is the *one* kind of mapping that this cannot happen
    for - because then you have the same page mapped only at one
    particular virtual address (and all modern x86's are entirely coherent
    in the pipeline for that case, afaik).

    > Now if there is file which you have both W and X SELinux permissions
    > (which is rare, but not impossible) you could map it in two places.  So
    > we can (and do) build SELinux sandboxes which address this.

    So the cases that matter are file-backed and various shared memory setups.

    Linus
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