linux-kernel - Re: [PATCH 4.9] hugetlbfs: flush TLBs correctly after huge_pmd

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Message-Id: <C1607574-0A6F-4CEC-B488-795750EEF968@gmail.com>
Date:   Fri, 26 Nov 2021 09:49:01 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     Anton Ivanov <anton.ivanov@...bridgegreys.com>
Cc:     Nick Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-ia64@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-arch <linux-arch@...r.kernel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH 4.9] hugetlbfs: flush TLBs correctly after
 huge_pmd_unshare


> On Nov 26, 2021, at 2:21 AM, Anton Ivanov <anton.ivanov@...bridgegreys.com> 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.