Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re:[RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

[Linus Torvalds]

On Wed, Jan 18, 2012 at 7:04 AM, Eric Paris <eparis@xxxxxxxxxx> 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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