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Subject: Re: [PATCH 4.9] hugetlbfs: flush TLBs correctly after
 huge_pmd_unshare
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <7a2feed4-7c73-c7ad-881e-c980235c8293@cambridgegreys.com>
Date:   Fri, 26 Nov 2021 09:49:01 -0800
Cc:     Nick Piggin <npiggin@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
        linux-um@lists.infradead.org, linux-arm-kernel@lists.infradead.org,
        linux-arch <linux-arch@vger.kernel.org>,
        Mike Kravetz <mike.kravetz@oracle.com>
Content-Transfer-Encoding: quoted-printable
Message-Id: <C1607574-0A6F-4CEC-B488-795750EEF968@gmail.com>
References: <3BD89231-2CB9-4CE5-B0FA-5B58419D7CB8@gmail.com>
 <7a2feed4-7c73-c7ad-881e-c980235c8293@cambridgegreys.com>
To:     Anton Ivanov <anton.ivanov@cambridgegreys.com>
Precedence: bulk


> On Nov 26, 2021, at 2:21 AM, Anton Ivanov =
<anton.ivanov@cambridgegreys.com> wrote:
>=20
>=20
>=20
> 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
>=20
> I do not quite see the rationale for patching um
>=20
> It supports only standard size pages. You should not be able to map a =
huge page there (and hugetlbfs).
>=20
> 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.