When parsing the capability list make sure the offset is between the
MMIO region mapped in 'regs', or else the kernel hits a page fault.

This fault has been seen when running as a Xen PVH dom0, which doesn't
have the MMIO regions mapped into the domain physical memory map,
despite having the device reported in the ACPI DSDT table. This
results in reporting a capability offset of 0xffff (because the kernel
is accessing unpopulated memory), and such offset is outside of the
mapped region.

Adding the check is harmless, and prevents buggy or broken systems
from crashing the kernel if the MMIO region is not properly reported.

Fixes: 91d898e51e60 ('pinctrl: intel: Convert capability list to features')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
---
Resend because I've missed adding the maintainers, sorry for the spam.
---
 drivers/pinctrl/intel/pinctrl-intel.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/pinctrl/intel/pinctrl-intel.c b/drivers/pinctrl/intel/pinctrl-intel.c
index 8085782cd8f9..bc8b990d8021 100644
--- a/drivers/pinctrl/intel/pinctrl-intel.c
+++ b/drivers/pinctrl/intel/pinctrl-intel.c
@@ -1481,16 +1481,22 @@ static int intel_pinctrl_probe(struct platform_device *pdev,
 
 	for (i = 0; i < pctrl->ncommunities; i++) {
 		struct intel_community *community = &pctrl->communities[i];
+		struct resource *res;
 		void __iomem *regs;
+		size_t size;
 		u32 offset;
 		u32 value;
 
 		*community = pctrl->soc->communities[i];
 
-		regs = devm_platform_ioremap_resource(pdev, community->barno);
+		regs = devm_platform_get_and_ioremap_resource(pdev,
+							      community->barno,
+							      &res);
 		if (IS_ERR(regs))
 			return PTR_ERR(regs);
 
+		size = res->end - res->start;
+
 		/* Determine community features based on the revision */
 		value = readl(regs + REVID);
 		if (((value & REVID_MASK) >> REVID_SHIFT) >= 0x94) {
@@ -1519,6 +1525,12 @@ static int intel_pinctrl_probe(struct platform_device *pdev,
 				break;
 			}
 			offset = (value & CAPLIST_NEXT_MASK) >> CAPLIST_NEXT_SHIFT;
+			if (offset >= size) {
+				dev_err(&pdev->dev,
+					"wrong capability offset: %#x\n",
+					offset);
+				return -ENOENT;
+			}
 		} while (offset);
 
 		dev_dbg(&pdev->dev, "Community%d features: %#08x\n", i, community->features);
-- 
2.30.1

On Wed, Mar 24, 2021 at 01:31:18PM +0100, Roger Pau Monne wrote:
> When parsing the capability list make sure the offset is between the
> MMIO region mapped in 'regs', or else the kernel hits a page fault.
> 
> This fault has been seen when running as a Xen PVH dom0, which doesn't
> have the MMIO regions mapped into the domain physical memory map,
> despite having the device reported in the ACPI DSDT table. This
> results in reporting a capability offset of 0xffff (because the kernel
> is accessing unpopulated memory), and such offset is outside of the
> mapped region.
> 
> Adding the check is harmless, and prevents buggy or broken systems
> from crashing the kernel if the MMIO region is not properly reported.

Thanks for the report.

Looking into the code I would like rather see the explicit comparison to 0xffff
or ~0 against entire register b/c it's (one of) standard way of devices to tell
that something is not supported.

Moreover, it seems you are bailing out and basically denying driver to load.
This does look that capability is simply the first register that blows the setup.
I think you have to fix something into Xen to avoid loading these drivers or
check with something like pci_device_is_present() approach.

> Fixes: 91d898e51e60 ('pinctrl: intel: Convert capability list to features')
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
> Cc: Andy Shevchenko <andy@kernel.org>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Cc: linux-gpio@vger.kernel.org
> ---
> Resend because I've missed adding the maintainers, sorry for the spam.

I have a script to make it easier: https://github.com/andy-shev/home-bin-tools/blob/master/ge2maintainer.sh

-- 
With Best Regards,
Andy Shevchenko