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);