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.

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