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Fri, 12 Jan 2024 09:31:41 -0800 (PST) MIME-Version: 1.0 References: <20240112013935.1474648-1-surenb@google.com> <511e07da-9b34-4707-8f5a-f1e534c4445a@redhat.com> In-Reply-To: <511e07da-9b34-4707-8f5a-f1e534c4445a@redhat.com> From: Suren Baghdasaryan Date: Fri, 12 Jan 2024 09:31:28 -0800 Message-ID: Subject: Re: [PATCH 1/1] userfaultfd: avoid huge_zero_page in UFFDIO_MOVE To: David Hildenbrand Cc: akpm@linux-foundation.org, sfr@canb.auug.org.au, peterx@redhat.com, aarcange@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzbot+705209281e36404998f6@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 6D9BE40020 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: ogu5jgz5kreokcsngj34ich4izztmxfa X-HE-Tag: 1705080703-947962 X-HE-Meta: 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 ob3PoEoM IBxV8zMwADbvG3dj/B1S0snyXSncYC/Yjtntr2ES9FtcS4tQ6gXp/tExT+nYsgJ4urDId8Q/Zw1uJTExs/+8ozF8fvBAFaHMF7ZNebdAarZd0b6ZnJYRLinQCsC3dCBtIrBiAlxXwxkiOv7U= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jan 12, 2024 at 12:57=E2=80=AFAM David Hildenbrand wrote: > > On 12.01.24 02:39, Suren Baghdasaryan wrote: > > While testing UFFDIO_MOVE ioctl, syzbot triggered VM_BUG_ON_PAGE caused > > by a call to PageAnonExclusive() with a huge_zero_page as a parameter. > > UFFDIO_MOVE does not yet handle zeropages and returns EBUSY when one is > > encountered. Add an early huge_zero_page check in the PMD move path > > to avoid this situation. > > > > Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com > > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") > > Signed-off-by: Suren Baghdasaryan > > --- > > Applies cleanly over linux-next, mm-stable and mm-unstable branches > > > > mm/userfaultfd.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > > index 216ab4c8621f..20e3b0d9cf7e 100644 > > --- a/mm/userfaultfd.c > > +++ b/mm/userfaultfd.c > > @@ -1393,6 +1393,12 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, = struct mm_struct *mm, > > err =3D -ENOENT; > > break; > > } > > + /* Avoid moving zeropages for now */ > > + if (is_huge_zero_pmd(*src_pmd)) { > > + spin_unlock(ptl); > > + err =3D -EBUSY; > > + break; > > + } > > As an alternative (and more future proof?) just reject anything that is > not an anon folio as well? Yes, but I'm going to remove this check shortly, once zeropage movement patch is ready. > > Anyhow, this should handle the issue at hand. > > Acked-by: David Hildenbrand Thanks! > > -- > Cheers, > > David / dhildenb >