Re: [PATCH 4.9] hugetlbfs: flush TLBs correctly after huge_pmd_unshare

[Anton Ivanov]

On 26/11/2021 17:49, Nadav Amit wrote:
> > On Nov 26, 2021, at 2:21 AM, Anton Ivanov <anton.ivanov@xxxxxxxxxxxxxxxxxx> wrote:
> >
> >
> >
> > On 26/11/2021 06:08, Nadav Amit wrote:
> > > Below is a patch to address CVE-2021-4002 [1] that I created to backport
> > > to 4.9. The stable kernels of 4.14 and prior ones do not have unified
> > > TLB flushing code, and I managed to mess up the arch code a couple of
> > > times.
> > > Now that the CVE is public, I would appreciate your review of this
> > > patch. I send 4.9 for review - the other ones (4.14 and prior) are
> > > pretty similar.
> > > [1] https://www.openwall.com/lists/oss-security/2021/11/25/1
> > > Thanks,
> > > Nadav
> >
> > I do not quite see the rationale for patching um
> >
> > It supports only standard size pages. You should not be able to map a huge page there (and hugetlbfs).
> >
> > I have "non-standard page size" somewhere towards the end of my queue, but it keeps falling through - not enough spare time to work on it.
>
> Thanks for your review.
>
> I did not look at the dependencies, so I did not even look if
> hugetlbfs depends on !um.
>
> Do you prefer that for um, I will just do a BUG()? I prefer
> to have a stub just to avoid potential build issues.

Stub will be fine.

I was just checking in case I missed something.

Brgds,

--
Anton R. Ivanov
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