linux-kernel - Re: [PATCH v6] PCI: imx6: limit DBI register length

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Date:   Mon, 25 Feb 2019 14:47:30 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     "stefan@...er.ch" <stefan@...er.ch>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "gustavo.pimentel@...opsys.com" <gustavo.pimentel@...opsys.com>,
        "tpiepho@...inj.com" <tpiepho@...inj.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>
Subject: Re: [PATCH v6] PCI: imx6: limit DBI register length

On Mon, 2019-02-25 at 15:25 +0100, Stefan Agner wrote:
> Define the length of the DBI registers and limit config space to its
> length. This makes sure that the kernel does not access registers
> beyond that point, avoiding the following abort on a i.MX 6Quad:
>   # cat /sys/devices/soc0/soc/1ffc000.pcie/pci0000\:00/0000\:00\:00.0/config
>   [  100.021433] Unhandled fault: imprecise external abort (0x1406) at 0xb6ea7000
>   ...
>   [  100.056423] PC is at dw_pcie_read+0x50/0x84
>   [  100.060790] LR is at dw_pcie_rd_own_conf+0x44/0x48
>  
> +static void imx6_pcie_quirk(struct pci_dev *dev)
> +{
> +	struct pci_bus *bus = dev->bus;
> +	struct pcie_port *pp = bus->sysdata;
> +
> +	if (bus->number == pp->root_bus_nr) {
> +		struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +		struct imx6_pcie *imx6_pcie = to_imx6_pcie(pci);
> +
> +		/*
> +		 * Limit config length to avoid the kernel reading beyond
> +		 * the register set and causing an abort on i.MX 6Quad
> +		 */
> +		dev->cfg_size = imx6_pcie->drvdata->dbi_length;
> +	}
> +}
> +DECLARE_PCI_FIXUP_HEADER(PCI_ANY_ID, PCI_ANY_ID, imx6_pcie_quirk);

Are you sure that this quirk is only applied to imx6-pcie?
Superficially it looks like it would apply to all PCI roots and this
could be a problem on configs which enable all drivers, like arm64.

Maybe the linker magic inside DECLARE_PCI_FIXUP deals with that, in
that case I apologize.

--
Regards,
Leonard