Re: [PATCH V4 05/16] soc: tegra: pmc: Avoid extra remapping of PMC registers

Thierry Reding
2016-01-14T13:45:26Z

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On Fri, Dec 04, 2015 at 02:57:06PM +0000, Jon Hunter wrote:
> During early initialisation, the PMC registers are mapped and the PMC SoC
> data is populated in the PMC data structure. This allows other drivers
> access the PMC register space, via the public tegra PMC APIs, prior to
> probing the PMC device.
>
> When the PMC device is probed, the PMC registers are mapped again and if
> successful the initial mapping is freed. If the probing of the PMC device
> fails after the registers are remapped, then the registers will be
> unmapped and hence the pointer to the PMC registers will be invalid. This
> could lead to a potential crash, because once the PMC SoC data pointer is
> populated, the driver assumes that the PMC register mapping is also valid
> and a user calling any of the public tegra PMC APIs could trigger an
> exception because these APIs don't check that the mapping is still valid.
>
> Rather than adding a test to see if the PMC register mapping is valid,
> fix this by removing the second mapping of the PMC registers and reserve
> the memory region for the PMC registers during early initialisation where
> the initial mapping is created. During the probing of the PMC simply check
> that the PMC registers have been mapped.
>
> Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
> ---
> drivers/soc/tegra/pmc.c | 19 +++++++++----------
> 1 file changed, 9 insertions(+), 10 deletions(-)

devm_ioremap_resource() was used on purpose to make sure we get a proper
name assigned to the memory region in /proc/iomem. As it is, there will
be no name associated with it, which I think is unfortunate. As such I'd
prefer keeping that call and instead fix the issue with the invalid
mapping by making sure that pmc->base is assigned only after nothing can
fail in probe anymore.

> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
> index e60fc2d33c94..fdd1a8d0940f 100644
> --- a/drivers/soc/tegra/pmc.c
> +++ b/drivers/soc/tegra/pmc.c
> @@ -807,22 +807,17 @@ out:
>
> static int tegra_pmc_probe(struct platform_device *pdev)
> {
> - void __iomem *base = pmc->base;

The alternative that I proposed above would entail not setting this...

> - struct resource *res;
> int err;
>
> + if (!pmc->base) {
> + dev_err(&pdev->dev, "base address is not configured\n");
> + return -ENXIO;
> + }
> +
> err = tegra_pmc_parse_dt(pmc, pdev->dev.of_node);
> if (err < 0)
> return err;
>
> - /* take over the memory region from the early initialization */
> - res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> - pmc->base = devm_ioremap_resource(&pdev->dev, res);

... and storing the result of the mapping in "base" instead...

> - if (IS_ERR(pmc->base))
> - return PTR_ERR(pmc->base);
> -
> - iounmap(base);

... and move the unmap to the very end of the probe function, which
would look something like:

/* take over the memory region from the early initialization */
iounmap(pmc->base);
pmc->base = base;

That way the mapping in "base" will automatically be undone upon error
and the pmc->base will only be overridden when it's certain that the
probe will succeed.

What do you think?

Thierry

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