drm/amd/pm: Reject negative values in thermal_throttling_logging

Discovery: Fuzzing for secure supply chain requirements
Tool: amd_fuzzing_sysfs (IGT test)

The thermal_throttling_logging sysfs store function accepts negative
values like -1 and -9999999, which are nonsensical for a logging interval.

Current behavior:
- Values <= 0 disable logging (intended for 0 only)
- Values 1-3600 enable logging with interval in seconds
- Negative values are accepted and treated as disable

Issue:
Large negative values like -9999999 make no semantic sense and could
indicate input validation bypass attempts. While they functionally
disable logging (same as 0), accepting arbitrary negative values
suggests inadequate input validation.

Fix:
Add explicit check to reject values < 0 before processing.
Only accept:
- 0: disable thermal throttling logging
- 1-3600: enable with interval in seconds (existing validation)

This improves input validation and makes the interface more robust.

Test Results Before Fix:
  thermal_throttling_logging: 6 failures
  - Accepted: 0, -1, -9999999, -2147483648, empty string, 0777

Test Results After Fix:
  thermal_throttling_logging: 3 failures
  - Rejected: -1, -9999999, -2147483648 (now return -EINVAL)
  - Remaining: empty string (VFS behavior), 0 (valid), 0777 (octal)

Tested: amd_fuzzing_sysfs IGT test

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Jesse Zhang <jesse.zhang@amd.com>

Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/amdgpu_pm.c

@@ -1634,6 +1634,10 @@ static ssize_t amdgpu_set_thermal_throttling_logging(struct device *dev,
 	if (ret)
 		return ret;
 
+	/* Reject negative values - only 0 (disable) or 1-3600 (seconds) are valid */
+	if (throttling_logging_interval < 0)
+		return -EINVAL;
+
 	if (throttling_logging_interval > 3600)
 		return -EINVAL;