[PATCH v2 i-g-t 2/2] tests/intel/xe_compute: check root-only write permission for ccs_mode

[Peter Senna Tschudin <peter.senna@linux.intel.com>]

Add a call to igt_fs_check_root_perm() in test_ccs_mode() to verify that
the "ccs_mode" sysfs attribute is writable only by root. This enforces a
security requirement that only root can modify "ccs_mode", preventing
unintended or unauthorized writes by other users.

Signed-off-by: Peter Senna Tschudin <peter.senna@linux.intel.com>
---
Changes from v1:
 - Moved the test to after the existing test
 - Check for file not found and skip when it is the case

 tests/intel/xe_compute.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/tests/intel/xe_compute.c b/tests/intel/xe_compute.c
index 310093fc5..eb2410a0a 100644
--- a/tests/intel/xe_compute.c
+++ b/tests/intel/xe_compute.c
@@ -14,6 +14,7 @@
 #include <string.h>
 
 #include "igt.h"
+#include "igt_fs.h"
 #include "igt_sysfs.h"
 #include "intel_compute.h"
 #include "xe/xe_ioctl.h"
@@ -88,7 +89,7 @@ test_ccs_mode(void)
 {
 	struct drm_xe_engine_class_instance *hwe;
 	u32 gt, m, ccs_mode, vm, q, num_slices;
-	int fd, gt_fd, num_gt_with_ccs_mode = 0;
+	int fd, file_perm_res, gt_fd, num_gt_with_ccs_mode = 0;
 	uint64_t gt_mask = get_gt_mask();
 
 	/*
@@ -102,6 +103,20 @@ test_ccs_mode(void)
 		num_gt_with_ccs_mode++;
 		gt_fd = gt_sysfs_open(gt);
 		igt_assert(igt_sysfs_printf(gt_fd, "ccs_mode", "%u", 0) < 0);
+
+		/* Check if ccs_mode is writeble only by root. Having root only
+		 * write permission is a security requirement.
+		 */
+		file_perm_res = igt_fs_check_root_perm(gt_fd, "ccs_mode");
+		if (file_perm_res == -ENOENT) {
+			igt_skip("ccs_mode sysfs entry not found\n");
+		} else if (file_perm_res < 0) {
+			igt_skip("Cannot stat ccs_mode file\n");
+		} else {
+			igt_assert_f(file_perm_res == 0,
+				     "ccs_mode sysfs entry has incorrect permissions\n");
+		}
+
 		for (m = 1; m <= num_slices; m++) {
 			/* compute slices are to be equally distributed among enabled engines */
 			if (num_slices % m) {
-- 
2.43.0