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When both hwmon and hwmon drvdata (on which hwmon depends) are device
managed resources, the expectation, on device unbind, is that hwmon will be
released before drvdata. However, in i915 there are two separate code
paths, which both release either drvdata or hwmon and either can be
released before the other. These code paths (for device unbind) are as
follows (see also the bug referenced below):
Call Trace:
release_nodes+0x11/0x70
devres_release_group+0xb2/0x110
component_unbind_all+0x8d/0xa0
component_del+0xa5/0x140
intel_pxp_tee_component_fini+0x29/0x40 [i915]
intel_pxp_fini+0x33/0x80 [i915]
i915_driver_remove+0x4c/0x120 [i915]
i915_pci_remove+0x19/0x30 [i915]
pci_device_remove+0x32/0xa0
device_release_driver_internal+0x19c/0x200
unbind_store+0x9c/0xb0
and
Call Trace:
release_nodes+0x11/0x70
devres_release_all+0x8a/0xc0
device_unbind_cleanup+0x9/0x70
device_release_driver_internal+0x1c1/0x200
unbind_store+0x9c/0xb0
This means that in i915, if use devm, we cannot gurantee that hwmon will
always be released before drvdata. Which means that we have a uaf if hwmon
sysfs is accessed when drvdata has been released but hwmon hasn't.
The only way out of this seems to be do get rid of devm_ and release/free
everything explicitly during device unbind.
v2: Change commit message and other minor code changes
v3: Cleanup from i915_hwmon_register on error (Armin Wolf)
v4: Eliminate potential static analyzer warning (Rodrigo)
Eliminate fetch_and_zero (Jani)
v5: Restore previous logic for ddat_gt->hwmon_dev error return (Andi)
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10366
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240417145646.793223-1-ashutosh.dixit@intel.com
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.