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

[Nadav Amit <nadav.amit@xxxxxxxxx>]

> 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.