7bf168c8fe
When running the latest kernel on an sc7180 with KASAN I got this splat: BUG: KASAN: slab-out-of-bounds in a6xx_gpu_init+0x618/0x644 Read of size 4 at addr ffffff8088f36100 by task kworker/7:1/58 CPU: 7 PID: 58 Comm: kworker/7:1 Not tainted 5.11.0+ #3 Hardware name: Google Lazor (rev1 - 2) with LTE (DT) Workqueue: events deferred_probe_work_func Call trace: dump_backtrace+0x0/0x3a8 show_stack+0x24/0x30 dump_stack+0x174/0x1e0 print_address_description+0x70/0x2e4 kasan_report+0x178/0x1bc __asan_report_load4_noabort+0x44/0x50 a6xx_gpu_init+0x618/0x644 adreno_bind+0x26c/0x438 This is because the speed bin is defined like this: gpu_speed_bin: gpu_speed_bin@1d2 { reg = <0x1d2 0x2>; bits = <5 8>; }; As you can see the "length" is 2 bytes. That means that the nvmem subsystem allocates only 2 bytes. The GPU code, however, was casting the pointer allocated by nvmem to a (u32 *) and dereferencing. That's not so good. Let's fix this to just use the nvmem_cell_read_u16() accessor function which simplifies things and also gets rid of the splat. Let's also put an explicit conversion from little endian in place just to make things clear. The nvmem subsystem today is assuming little endian and this makes it clear. Specifically, the way the above sc7180 cell is interpreted: NVMEM: +--------+--------+--------+--------+--------+ | ...... | 0x1d3 | 0x1d2 | ...... | 0x000 | +--------+--------+--------+--------+--------+ ^ ^ msb lsb You can see that the least significant data is at the lower address which is little endian. NOTE: someone who is truly paying attention might wonder about me picking the "u16" version of this accessor instead of the "u8" (since the value is 8 bits big) or the u32 version (just for fun). At the moment you need to pick the accessor that exactly matches the length the cell was specified as in the device tree. Hopefully future patches to the nvmem subsystem will fix this. Fixes: fe7952c629da ("drm/msm: Add speed-bin support to a618 gpu") Signed-off-by: Douglas Anderson <dianders@chromium.org> Signed-off-by: Rob Clark <robdclark@chromium.org>
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 Restructured Text 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.