drm/amd/pm: fix pptable use-after-free

drm/amd/pm: fix pptable use-after-free

amdgpu_dpm_get_pp_table() returns a pointer to a driver-owned power table
after dropping adev->pm.mutex. The sysfs path then copies from that pointer.
A concurrent pp_table write can replace and free the allocation during the
copy, causing a use-after-free.

Change the DPM interface to copy into caller-provided storage while the mutex
is held. Keep the size-only query for attribute discovery without exposing
the driver-owned pointer.

Fixes: 1684d3ba4885 ("drm/amd/amdgpu: change pptable output format from ASCII to binary")
Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit f6eed7acfd30099ef7baeb6ba45bb59daad80631)
Cc: stable@vger.kernel.org