[DTrace-devel] [PATCH 2/2] Forbid increasing iregs above default

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

If iregs is set larger than the default, code is generated using
nonexistent registers and the BPF verifier emits confusing errors.

Simply do not allow users to increase iregs beyond the default.

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 libdtrace/dt_options.c            |  2 +-
 test/unittest/options/err.iregs.d | 16 ++++++++++++++++
 test/unittest/options/err.iregs.r |  2 ++
 3 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 test/unittest/options/err.iregs.d
 create mode 100644 test/unittest/options/err.iregs.r

diff --git a/libdtrace/dt_options.c b/libdtrace/dt_options.c
index 1c32dc3d..d25b2ac9 100644
--- a/libdtrace/dt_options.c
+++ b/libdtrace/dt_options.c
@@ -264,7 +264,7 @@ dt_opt_iregs(dtrace_hdl_t *dtp, const char *arg, uintptr_t option)
 {
 	int n;
 
-	if (arg == NULL || (n = atoi(arg)) <= 0)
+	if (arg == NULL || (n = atoi(arg)) <= 0 || n > DIF_DIR_NREGS)
 		return dt_set_errno(dtp, EDT_BADOPTVAL);
 
 	dtp->dt_conf.dtc_difintregs = n;
diff --git a/test/unittest/options/err.iregs.d b/test/unittest/options/err.iregs.d
new file mode 100644
index 00000000..ace21d6d
--- /dev/null
+++ b/test/unittest/options/err.iregs.d
@@ -0,0 +1,16 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Licensed under the Universal Permissive License v 1.0 as shown at
+ * http://oss.oracle.com/licenses/upl.
+ */
+
+/* DTrace should recognize when iregs is too great for # of BPF registers */
+#pragma D option iregs=9
+
+BEGIN
+{
+	a = 1;
+	trace(a);
+	exit(0);
+}
diff --git a/test/unittest/options/err.iregs.r b/test/unittest/options/err.iregs.r
new file mode 100644
index 00000000..536c3eb8
--- /dev/null
+++ b/test/unittest/options/err.iregs.r
@@ -0,0 +1,2 @@
+-- @@stderr --
+dtrace: failed to compile script test/unittest/options/err.iregs.d: line 9: failed to set option 'iregs' to '9': Invalid value for specified option
-- 
2.18.4