Re: arm32 insecure W+X mapping

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Tim Harvey <tharvey@gateworks.com>
Cc: Fabio Estevam <festevam@gmail.com>,
	Shawn Guo <shawnguo@kernel.org>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Linux ARM Mailing List <linux-arm-kernel@lists.infradead.org>,
	Lee Jones <lee.jones@linaro.org>,
	Robin Murphy <robin.murphy@arm.com>,
	NXP Linux Team <linux-imx@nxp.com>
Subject: Re: arm32 insecure W+X mapping
Date: Mon, 20 Sep 2021 22:13:08 +0100	[thread overview]
Message-ID: <YUj5ZFTsRNxWdyOY@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAJ+vNU0NTUnuu0DHJDDyTR81ThHKdVL9xVweCwg7RVtNDfyVjQ@mail.gmail.com>

On Mon, Sep 20, 2021 at 01:56:51PM -0700, Tim Harvey wrote:
> On Mon, Sep 20, 2021 at 9:22 AM Russell King (Oracle)
> <linux@armlinux.org.uk> wrote:
> >
> > On Wed, Sep 15, 2021 at 06:44:56AM -0300, Fabio Estevam wrote:
> > > Not sure if this is related or not to the following behavior that I am seeing.
> > >
> > > On 5.15-rc1 I see the following on an imx6dl based board:
> > >
> > > [    0.123336] imx6q_suspend_init: failed to find ocram device!
> >
> > Looking at the platforms I currently have, two imx6q which booted 5.13
> > do not have this problem, but one imx6dl that booted 5.14 does seem to
> > spit out this message.
> >
> > What I do notice is that in the 5.14 case, /proc/iomem reports that the
> > ocram device does exist:
> >
> > 00900000-0091ffff : 900000.sram sram@900000
> >
> > so I'm suspecting an init ordering issue.
> >
> > It looks on the face of it to be a regression between 5.13 and 5.14.
> > I'm guessing that the sram device isn't being probed early enough.
> > Maybe some of the initialisation/device model debug options can
> > identify what changed?
> >
> 
> Here's what I see on both imx6dl and imx6q with both CONFIG_DEBUG_WX
> and CONFIG_SUSPEND enabled:
> 5.13: 'Checked W+X mappings: FAILED, 1 W+X pages found' on both imx6q and imx6dl
> 5.14: No W+X failure on either board.... so something different for sure
> 5.15-rc2: same as 5.14
> 
> So my results differ from yours but showed that something has been
> fixed vs regressed. I'll bisect and see if I can figure out when my
> original issue I reported here went away.

I'm not sure we are disagreeing. I don't have CONFIG_DEBUG_WX enabled,
but in 5.13, I see in /sys/kernel/debug/kernel_page_tables:

0xf087d000-0xf087e000           4K KERNEL      RW x  SHD MEM/BUFFERABLE/WC

and /proc/vmallocinfo has:

0xf087d000-0xf087f000    8192 imx6_pm_common_init+0x13c/0x390 phys=0x00900000 ioremap

So this will give a W+X failure.

Under 5.14, there is no mapping for this RAM in kernel_page_tables nor
vmallocinfo - which is not surprising because imx6_pm_common_init()
said it failed to find the ocram, and it only gets one shot at it.
So there won't be a W+X failure.

In other words, we are in complete agreement.

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