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From: Barry Song <21cnbao@gmail.com>
Date: Tue, 19 Mar 2024 10:37:32 +1300
Message-ID: <CAGsJ_4xTx_FRCrh0KQ4dGAyHisWaK9kUa5UPETWcLnqPwxPkkg@mail.gmail.com>
Subject: Re: [syzbot] [mm?] kernel BUG in sg_init_one
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Yosry Ahmed <yosryahmed@google.com>, Nhat Pham <nphamcs@gmail.com>, 
	syzbot <syzbot+adbc983a1588b7805de3@syzkaller.appspotmail.com>, 
	akpm@linux-foundation.org, chengming.zhou@linux.dev, 
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, 
	syzkaller-bugs@googlegroups.com, Barry Song <v-songbaohua@oppo.com>
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On Tue, Mar 19, 2024 at 10:33=E2=80=AFAM Johannes Weiner <hannes@cmpxchg.or=
g> wrote:
>
> On Tue, Mar 19, 2024 at 10:15:43AM +1300, Barry Song wrote:
> > On Tue, Mar 19, 2024 at 10:10=E2=80=AFAM Johannes Weiner <hannes@cmpxch=
g.org> wrote:
> > >
> > > On Mon, Mar 18, 2024 at 01:17:19PM -0700, Yosry Ahmed wrote:
> > > > On Mon, Mar 18, 2024 at 11:00=E2=80=AFAM Nhat Pham <nphamcs@gmail.c=
om> wrote:
> > > > >
> > > > > On Mon, Mar 18, 2024 at 9:58=E2=80=AFAM syzbot
> > > > > <syzbot+adbc983a1588b7805de3@syzkaller.appspotmail.com> wrote:
> > > > > >
> > > > > > Hello,
> > > > > >
> > > > > > syzbot found the following issue on:
> > > > > >
> > > > > > HEAD commit:    e5eb28f6d1af Merge tag 'mm-nonmm-stable-2024-03=
-14-09-36' ..
> > > > > > git tree:       upstream
> > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=3D130=
43abe180000
> > > > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=3D19b=
b57c23dffc38e
> > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=3Dadbc9=
83a1588b7805de3
> > > > > > compiler:       arm-linux-gnueabi-gcc (Debian 12.2.0-14) 12.2.0=
, GNU ld (GNU Binutils for Debian) 2.40
> > > > > > userspace arch: arm
> > > > > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=3D1=
706d231180000
> > > > > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=3D13b=
a7959180000
> > > > > >
> > > > > > Downloadable assets:
> > > > > > disk image (non-bootable): https://storage.googleapis.com/syzbo=
t-assets/8ead8862021c/non_bootable_disk-e5eb28f6.raw.xz
> > > > > > vmlinux: https://storage.googleapis.com/syzbot-assets/0a7371c63=
ff2/vmlinux-e5eb28f6.xz
> > > > > > kernel image: https://storage.googleapis.com/syzbot-assets/7539=
441b4add/zImage-e5eb28f6.xz
> > > > > >
> > > > > > IMPORTANT: if you fix the issue, please add the following tag t=
o the commit:
> > > > > > Reported-by: syzbot+adbc983a1588b7805de3@syzkaller.appspotmail.=
com
> > > > > >
> > > > > > ------------[ cut here ]------------
> > > > > > kernel BUG at include/linux/scatterlist.h:187!
> > > > >
> > > > > Looks like the provided buffer is invalid:
> > > > >
> > > > > #ifdef CONFIG_DEBUG_SG
> > > > > BUG_ON(!virt_addr_valid(buf));
> > > > > #endif
> > > > >
> > > > > which is "src" from:
> > > > >
> > > > > sg_init_one(&input, src, entry->length);
> > > > >
> > > > > Looking at the surrounding code and recent history, there's this
> > > > > commit that stands out:
> > > > >
> > > > > mm/zswap: remove the memcpy if acomp is not sleepable
> > > > > (sha: 270700dd06ca41a4779c19eb46608f076bb7d40e)
> > > > >
> > > > > which has the effect of, IIUC, using the zpool mapped memory dire=
ctly
> > > > > as src, instead of acomp_ctx->buffer (which was previously the ca=
se,
> > > > > as zsmalloc was not sleepable).
> > > > >
> > > > > This might not necessarily be a bug with that commit itself, but =
might
> > > > > have revealed another bug elsewhere.
> > > > >
> > > > > Anyway, cc-ing the author, Barry Song, to fact check me :) Will t=
ake a
> > > > > closer look later.
> > > >
> > > > I am not a highmem expert, but the reproducer has CONFIG_HIGHMEM=3D=
y,
> > > > and it seems like zs_map_object() may return a highmem address if t=
he
> > > > compressed object is entirely in a single page to avoid copying to =
a
> > > > buffer:
> > > >
> > > > if (off + class->size <=3D PAGE_SIZE) {
> > > >    /* this object is contained entirely within a page */
> > > >    area->vm_addr =3D kmap_atomic(page);
> > > >    ret =3D area->vm_addr + off;
> > > >    goto out;
> > > > }
> > > >
> > > > The virt_addr_valid() check seems to indicate that we expect a dire=
ct
> > > > map address in sg_init_one(), right?
> > >
> > > If the page is highmem, kmap_atomic() establishes a temporary mapping
> > > to it in the direct map, such that we have a legit kernel pointer to
> > > the memory. Otherwise the memcpy() in zswap also wouldn't work... Am =
I
> > > missing something?
> >
> > Right, we built a map but it is not a linear mapping. so we can't use
> > virt_to_page
> > on this kind of non-linear mapping.
> > kmap_to_page can handle both linear and non-linear, but  Ira's commit
> > added a WARN_ON_ONCE in it for non-linear mapping case.
>
> Ah, I misread what virt_addr_valid() does. It actually excludes
> kmap. Which, yes, makes sense, if the next line does virt_to_page()...
>
> Sorry about the noise.

no worries. I just wonder why Ira's commit ef6e06b2ef870 has added a
WARN_ON_ONCE
in kmap_to_page() given we still have many users :-)

drivers/fpga/fpga-mgr.c:                        pages[index] =3D
kmap_to_page((void *)p);
drivers/spi/spi.c:                              vm_page =3D kmap_to_page(bu=
f);
drivers/vfio/pci/pds/lm.c:                      pages[i] =3D
kmap_to_page((void *)p);
fs/erofs/data.c:                        .page =3D kmap_to_page(ptr),
fs/smb/server/transport_rdma.c:                 page =3D kmap_to_page(buf);
net/9p/trans_virtio.c:                          (*pages)[index] =3D
kmap_to_page(p);