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06249b4e69
When a scatterlists table of a GEM shmem object of size 4 GB or more is
populated with pages allocated from a folio, unsigned int .length
attribute of a scatterlist may get overflowed if total byte length of
pages allocated to that single scatterlist happens to reach or cross the
4GB limit. As a consequence, users of the object may suffer from hitting
unexpected, premature end of the object's backing pages.
[278.780187] ------------[ cut here ]------------
[278.780377] WARNING: CPU: 1 PID: 2326 at drivers/gpu/drm/i915/i915_mm.c:55 remap_sg+0x199/0x1d0 [i915]
...
[278.780654] CPU: 1 UID: 0 PID: 2326 Comm: gem_mmap_offset Tainted: G S U 6.17.0-rc1-CI_DRM_16981-ged823aaa0607+ #1 PREEMPT(voluntary)
[278.780656] Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER
[278.780658] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024
[278.780659] RIP: 0010:remap_sg+0x199/0x1d0 [i915]
...
[278.780786] Call Trace:
[278.780787] <TASK>
[278.780788] ? __apply_to_page_range+0x3e6/0x910
[278.780795] ? __pfx_remap_sg+0x10/0x10 [i915]
[278.780906] apply_to_page_range+0x14/0x30
[278.780908] remap_io_sg+0x14d/0x260 [i915]
[278.781013] vm_fault_cpu+0xd2/0x330 [i915]
[278.781137] __do_fault+0x3a/0x1b0
[278.781140] do_fault+0x322/0x640
[278.781143] __handle_mm_fault+0x938/0xfd0
[278.781150] handle_mm_fault+0x12c/0x300
[278.781152] ? lock_mm_and_find_vma+0x4b/0x760
[278.781155] do_user_addr_fault+0x2d6/0x8e0
[278.781160] exc_page_fault+0x96/0x2c0
[278.781165] asm_exc_page_fault+0x27/0x30
...
That issue was apprehended by the author of a change that introduced it,
and potential risk even annotated with a comment, but then never addressed.
When adding folio pages to a scatterlist table, take care of byte length
of any single scatterlist not exceeding max_segment.
Fixes:
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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.