features: tolerate EPERM in haveObjName and objNameAllowsDot

When loading ELFs using unprivileged tools or tests, EPERM causes dots and
underscores to be stripped from MapSpec.Name, causing strange results for
maps like .rodata.foo.

Also, only consider ErrNotSupported as conclusive and bubble up any other
errors to the caller. Most callers just check err != nil, but in case
someone indirectly relies on the sentinel, this should result in more
accurate output.

Signed-off-by: Timo Beckers <timo@isovalent.com>

Author: ti-mo

syscalls.go

@@ -179,10 +179,18 @@ var haveObjName = internal.NewFeatureTest("object names", func() error {
 		MapName:    sys.NewObjName("feature_test"),
 	}
 
+	// Tolerate EPERM as this runs during ELF loading which is potentially
+	// unprivileged. Only EINVAL is conclusive, thrown from CHECK_ATTR.
 	fd, err := sys.MapCreate(&attr)
-	if err != nil {
+	if errors.Is(err, unix.EPERM) {
+		return nil
+	}
+	if errors.Is(err, unix.EINVAL) {
 		return internal.ErrNotSupported
 	}
+	if err != nil {
+		return err
+	}
 
 	_ = fd.Close()
 	return nil
@@ -201,10 +209,19 @@ var objNameAllowsDot = internal.NewFeatureTest("dot in object names", func() err
 		MapName:    sys.NewObjName(".test"),
 	}
 
+	// Tolerate EPERM, otherwise MapSpec.Name has its dots removed when run by
+	// unprivileged tools. (bpf2go, other code gen). Only EINVAL is conclusive,
+	// thrown from bpf_obj_name_cpy().
 	fd, err := sys.MapCreate(&attr)
-	if err != nil {
+	if errors.Is(err, unix.EPERM) {
+		return nil
+	}
+	if errors.Is(err, unix.EINVAL) {
 		return internal.ErrNotSupported
 	}
+	if err != nil {
+		return err
+	}
 
 	_ = fd.Close()
 	return nil