drm/amd: Guard against bad data for ATIF ACPI method

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/amd: Guard against bad data for ATIF ACPI method If a BIOS provides bad data in response to an ATIF method call this causes a NULL pointer dereference in the caller. ``` ? show_regs (arch/x86/kernel/dumpstack.c:478 (discriminator 1)) ? __die (arch/x86/kernel/dumpstack.c:423 arch/x86/kernel/dumpstack.c:434) ? page_fault_oops (arch/x86/mm/fault.c:544 (discriminator 2) arch/x86/mm/fault.c:705 (discriminator 2)) ? do_user_addr_fault (arch/x86/mm/fault.c:440 (discriminator 1) arch/x86/mm/fault.c:1232 (discriminator 1)) ? acpi_ut_update_object_reference (drivers/acpi/acpica/utdelete.c:642) ? exc_page_fault (arch/x86/mm/fault.c:1542) ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623) ? amdgpu_atif_query_backlight_caps.constprop.0 (drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c:387 (discriminator 2)) amdgpu ? amdgpu_atif_query_backlight_caps.constprop.0 (drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c:386 (discriminator 1)) amdgpu ``` It has been encountered on at least one system, so guard for it. (cherry picked from commit c9b7c809b89f24e9372a4e7f02d64c950b07fdee)

References

• https://git.kernel.org/stable/c/58556dcbd5606a5daccaee73b2130bc16b48e025
• https://git.kernel.org/stable/c/43b4fa6e0e238c6e2662f4fb61d9f51c2785fb1d
• https://git.kernel.org/stable/c/234682910971732cd4da96fd95946e296e486b38
• https://git.kernel.org/stable/c/6032287747f874b52dc8b9d7490e2799736e035f
• https://git.kernel.org/stable/c/cd67af3c1762de4c2483ae4dbdd98f9ea8fa56e3
• https://git.kernel.org/stable/c/975ede2a7bec52b5da1428829b3439667c8a234b
• https://git.kernel.org/stable/c/1d7175f9c57b1abf9ecfbdfd53ea760761f52ffe
• https://git.kernel.org/stable/c/bf58f03931fdcf7b3c45cb76ac13244477a60f44