Received-SPF: pass (google.com: domain of linux-kernel+bounces-164298-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Tue, 30 Apr 2024 17:42:38 +0200
From: Joel Granados <j.granados@samsung.com>
To: Alexandre Ghiti <alex@ghiti.fr>
CC: Nam Cao <namcao@linutronix.de>, Mike Rapoport <rppt@kernel.org>, Andreas
	Dilger <adilger@dilger.ca>, =?utf-8?B?QmrDtnJuIFTDtnBlbA==?=
	<bjorn@kernel.org>, <linux-riscv@lists.infradead.org>, Thomas Gleixner
	<tglx@linutronix.de>, Andrew Morton <akpm@linux-foundation.org>,
	"ndesaulniers @ google . com" <ndesaulniers@google.com>, Luis Chamberlain
	<mcgrof@kernel.org>, Ingo Molnar <mingo@kernel.org>, Christophe Leroy
	<christophe.leroy@csgroup.eu>, Tejun Heo <tj@kernel.org>, Krister Johansen
	<kjlx@templeofstupid.com>, Changbin Du <changbin.du@huawei.com>, Arnd
	Bergmann <arnd@arndb.de>, Geert Uytterhoeven <geert+renesas@glider.be>,
	<linux-kernel@vger.kernel.org>, <stable@vger.kernel.org>
Subject: Re: [PATCH] init: fix allocated page overlapping with PTR_ERR
Message-ID: <20240430154238.nu6pebmdlpkxnk7q@joelS2.panther.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: multipart/signed; micalg="pgp-sha512";
	protocol="application/pgp-signature"; boundary="xorqn2blaq43v63q"
Content-Disposition: inline
In-Reply-To: <0049995a-07d0-4aaa-abc7-5bfc0dc22ace@ghiti.fr>
CMS-TYPE: 201P
References: <20240418102943.180510-1-namcao@linutronix.de>
	<CGME20240429125236eucas1p24219f2d332e0267794a2f87dea9f39c4@eucas1p2.samsung.com>
	<20240429125230.s5pbeye24iw5aurz@joelS2.panther.com>
	<20240430073056.bEG4-yk8@linutronix.de>
	<0049995a-07d0-4aaa-abc7-5bfc0dc22ace@ghiti.fr>

--xorqn2blaq43v63q
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Tue, Apr 30, 2024 at 10:37:59AM +0200, Alexandre Ghiti wrote:
> Hi Joel, Nam,
>=20
> On 30/04/2024 09:31, Nam Cao wrote:
> > On Mon, Apr 29, 2024 at 02:52:30PM +0200, Joel Granados wrote:
> >> On Thu, Apr 18, 2024 at 12:29:43PM +0200, Nam Cao wrote:
> >>> There is nothing preventing kernel memory allocators from allocating a
> >>> page that overlaps with PTR_ERR(), except for architecture-specific
> >>> code that setup memblock.
> >>>
> >>> It was discovered that RISCV architecture doesn't setup memblock
> >>> corectly, leading to a page overlapping with PTR_ERR() being allocate=
d,
> >>> and subsequently crashing the kernel (link in Close: )
> >>>
> >>> The reported crash has nothing to do with PTR_ERR(): the last page
> >>> (at address 0xfffff000) being allocated leads to an unexpected
> >>> arithmetic overflow in ext4; but still, this page shouldn't be
> >>> allocated in the first place.
> >>>
> >>> Because PTR_ERR() is an architecture-independent thing, we shouldn't
> >>> ask every single architecture to set this up. There may be other
> >>> architectures beside RISCV that have the same problem.
> >>>
> >>> Fix this one and for all by reserving the physical memory page that
> >>> may be mapped to the last virtual memory page as part of low memory.
> >>>
> >>> Unfortunately, this means if there is actual memory at this reserved
> >>> location, that memory will become inaccessible. However, if this page
> >>> is not reserved, it can only be accessed as high memory, so this
> >>> doesn't matter if high memory is not supported. Even if high memory is
> >>> supported, it is still only one page.
> >>>
> >>> Closes: https://lore.kernel.org/linux-riscv/878r1ibpdn.fsf@all.your.b=
ase.are.belong.to.us
> >>> Signed-off-by: Nam Cao <namcao@linutronix.de>
> >>> Cc: <stable@vger.kernel.org> # all versions
> >>> ---
> >>>   init/main.c | 1 +
> >>>   1 file changed, 1 insertion(+)
> >>>
> >>> diff --git a/init/main.c b/init/main.c
> >>> index 881f6230ee59..f8d2793c4641 100644
> >>> --- a/init/main.c
> >>> +++ b/init/main.c
> >>> @@ -900,6 +900,7 @@ void start_kernel(void)
> >>>   	page_address_init();
> >>>   	pr_notice("%s", linux_banner);
> >>>   	early_security_init();
> >>> +	memblock_reserve(__pa(-PAGE_SIZE), PAGE_SIZE); /* reserve last page=
 for ERR_PTR */
> >>>   	setup_arch(&command_line);
> >>>   	setup_boot_config();
> >>>   	setup_command_line(command_line);
> >>> --=20
> >>> 2.39.2
> >>>
> >> I received a similar(ish) report recently
> >> https://lore.kernel.org/oe-kbuild-all/202404211031.J6l2AfJk-lkp@intel.=
com/
> >> regarding RISC-V in init/mail.c. Here is the meat of the report in case
> >> you want to avoid going to the actual link:
> > This issue doesn't look like it has anything to do with this patch: this
> > patch is about overlapping of dynamically allocated memory, while I thi=
nk
> > the issue is about overlapping sections during linking (maybe something
> > wrong with riscv linker script?)
> >
> > Also, FWIW, this patch is not going to be in mainline because of a
> > regression.
> >
> > Nonetheless, I will have a look at this later.
>=20
>=20
> The config shows that it is a XIP kernel that comes with its own=20
> limitations (text is limited to 32MB for example), so I'm not surprised=
=20
> to see those overlaps.
>=20
> We already discussed the removal of randconfig builds on XIP configs,=20
> but IIRC it is not possible.

I just tested this going back until "2023-09-20 602bf1830798 (HEAD)
Merge branch 'for-6.7' into for-next  [Petr Mladek]" and I still saw the
overlapping errors.

Is this just something that happens always?

Best
--=20

Joel Granados

--xorqn2blaq43v63q
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=f44l
-----END PGP SIGNATURE-----

--xorqn2blaq43v63q--