[RFC 05/19] ktf: Implementation of ktf support for overriding function entry and return.

Knut Omang
2019-08-13T06:12:55Z

From: Alan Maguire <alan.maguire@oracle.com>

This is a very powerful and yet simple way to verify or modify
behaviour of kernel calls. It uses the same technique as the error
injection framework in kernel/fail_function.c to to override function
entry and return. In addition to error injection, this is very useful
to for instance verify that a particular API actually ends up being
called, and in the right way, as an effect of a test.

ktf_override.c: support for overriding function entry.
ktf_override.h: Function override support interface for KTF.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Knut Omang <knut.omang@oracle.com>
---
tools/testing/selftests/ktf/kernel/ktf_override.c | 45 ++++++++++++++++-
tools/testing/selftests/ktf/kernel/ktf_override.h | 15 +++++-
2 files changed, 60 insertions(+)
create mode 100644 tools/testing/selftests/ktf/kernel/ktf_override.c
create mode 100644 tools/testing/selftests/ktf/kernel/ktf_override.h

diff --git a/tools/testing/selftests/ktf/kernel/ktf_override.c b/tools/testing/selftests/ktf/kernel/ktf_override.c
new file mode 100644
index 0000000..7f046c8
--- /dev/null
+++ b/tools/testing/selftests/ktf/kernel/ktf_override.c
@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * Author: Alan Maguire <alan.maguire@oracle.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0
+ *
+ * ktf_override.c: support for overriding function entry.
+ */
+#include <linux/kprobes.h>
+#include <linux/ptrace.h>
+#include "ktf.h"
+#include "ktf_override.h"
+
+asmlinkage void ktf_just_return_func(void);
+
+asm(
+ ".type ktf_just_return_func, @function\n"
+ ".globl ktf_just_return_func\n"
+ "ktf_just_return_func:\n"
+ " ret\n"
+ ".size ktf_just_return_func, .-ktf_just_return_func\n"
+);
+
+void ktf_post_handler(struct kprobe *kp, struct pt_regs *regs,
+ unsigned long flags)
+{
+ /*
+ * A dummy post handler is required to prohibit optimizing, because
+ * jump optimization does not support execution path overriding.
+ */
+}
+EXPORT_SYMBOL(ktf_post_handler);
+
+void ktf_override_function_with_return(struct pt_regs *regs)
+{
+ KTF_SET_INSTRUCTION_POINTER(regs, (unsigned long)&ktf_just_return_func);
+}
+EXPORT_SYMBOL(ktf_override_function_with_return);
+NOKPROBE_SYMBOL(ktf_override_function_with_return);
+
+int ktf_register_override(struct kprobe *kp)
+{
+ return register_kprobe(kp);
+}
+EXPORT_SYMBOL(ktf_register_override);
diff --git a/tools/testing/selftests/ktf/kernel/ktf_override.h b/tools/testing/selftests/ktf/kernel/ktf_override.h
new file mode 100644
index 0000000..8a9cf39
--- /dev/null
+++ b/tools/testing/selftests/ktf/kernel/ktf_override.h
@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * Author: Alan Maguire <alan.maguire@oracle.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0
+ *
+ * ktf_override.h: Function override support interface for KTF.
+ */
+#include <linux/kprobes.h>
+#include "ktf.h"
+
+void ktf_post_handler(struct kprobe *kp, struct pt_regs *regs,
+ unsigned long flags);
+void ktf_override_function_with_return(struct pt_regs *regs);
+int ktf_register_override(struct kprobe *kp);
--
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