From: Daniel Latypov <[email protected]>
Allow function redirection using ftrace and kernel livepatch. This is
basically equivalent to the static_stub support in the previous patch,
but does not require the function being replaced to be modified (save
for the addition of KUNIT_STUBBABLE/noinline).
This is hidden behind the CONFIG_KUNIT_FTRACE_STUBS option, and has a
number of dependencies, including ftrace, livepatch and
CONFIG_KALLSYMS_ALL. As a result, it only works on architectures where
these are available.
You can run the KUnit example tests with the following:
$ ./tools/testing/kunit/kunit.py run --kunitconfig lib/kunit/stubs_example.kunitconfig --arch=x86_64
To the end user, replacing a function is very simple, e.g.
KUNIT_STUBBABLE void real_func(int n);
void replacement_func(int n);
/* in tests */
kunit_activate_ftrace_stub(test, real_func, replacement_func);
The implementation is inspired by Steven's snippet here [1].
Some more details:
* stubbing is automatically undone at the end of tests
* it can also be manually undone with kunit_deactive_ftrace_stub()
* stubbing only applies when current->kunit_test == test
* note: currently can't have more than one test running at a time
* KUNIT_STUBBABLE marks tests as noinline when CONFIG_KUNIT_STUBS is set
* this ensures we can actually stub all calls
* KUNIT_STUBBABLE_TRAMPOLINE is a version that evaluates to
__always_inline when stubbing is not enabled
* This may need to be used with a wrapper function.
* See the doc comment for more details.
Sharp-edges:
* kernel livepatch only works on some arches (not UML)
* if you don't use noinline/KUNIT_STUBBABLE, functions might be inlined
and thus none of this works:
* if it's always inlined, at least the attempt to stub will fail
* if it's sometimes inlined, then the stub silently won't work
[1] https://lore.kernel.org/lkml/[email protected]
Co-developed-by: David Gow <[email protected]>
Signed-off-by: David Gow <[email protected]>
Signed-off-by: Daniel Latypov <[email protected]>
---
include/kunit/ftrace_stub.h | 84 +++++++++++++++++
lib/kunit/Kconfig | 11 +++
lib/kunit/Makefile | 4 +
lib/kunit/ftrace_stub.c | 138 ++++++++++++++++++++++++++++
lib/kunit/kunit-example-test.c | 27 +++++-
lib/kunit/stubs_example.kunitconfig | 11 +++
6 files changed, 274 insertions(+), 1 deletion(-)
create mode 100644 include/kunit/ftrace_stub.h
create mode 100644 lib/kunit/ftrace_stub.c
create mode 100644 lib/kunit/stubs_example.kunitconfig
diff --git a/include/kunit/ftrace_stub.h b/include/kunit/ftrace_stub.h
new file mode 100644
index 000000000000..54c053b7e9c1
--- /dev/null
+++ b/include/kunit/ftrace_stub.h
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _KUNIT_FTRACE_STUB_H
+#define _KUNIT_FTRACE_STUB_H
+
+/** KUNIT_STUBBABLE - marks a function as stubbable when stubbing support is
+ * enabled.
+ *
+ * Stubbing uses ftrace internally, so we can only stub out functions when they
+ * are not inlined. This macro eavlautes to noinline when stubbing support is
+ * enabled to thus make it safe.
+ *
+ * If you cannot add this annotation to the function, you can instead use
+ * KUNIT_STUBBABLE_TRAMPOLINE, which is the same, but evaluates to
+ * __always_inline when stubbing is not enabled.
+ *
+ * Consider copy_to_user, which is marked as __always_inline:
+ *
+ * .. code-block:: c
+ * static KUNIT_STUBBABLE_TRAMPOLINE unsigned long
+ * copy_to_user_trampoline(void __user *to, const void *from, unsigned long n)
+ * {
+ * return copy_to_user(to, from, n);
+ * }
+ *
+ * Then we simply need to update our code to go through this function instead
+ * (in the places where we want to stub it out).
+ */
+#if IS_ENABLED(CONFIG_KUNIT_FTRACE_STUBS)
+#define KUNIT_STUBBABLE noinline
+#define KUNIT_STUBBABLE_TRAMPOLINE noinline
+#else
+#define KUNIT_STUBBABLE
+#define KUNIT_STUBBABLE_TRAMPOLINE __always_inline
+#endif
+
+struct kunit;
+
+/**
+ * kunit_activate_ftrace_stub() - makes all calls to @func go to @replacement during @test.
+ * @test: The test context object.
+ * @func: The function to stub out, must be annotated with KUNIT_STUBBABLE.
+ * @replacement: The function to replace @func with.
+ *
+ * All calls to @func will instead call @replacement for the duration of the
+ * current test. If called from outside the test's thread, the function will
+ * not be redirected.
+ *
+ * The redirection can be disabled again with kunit_deactivate_ftrace_stub().
+ *
+ * Example:
+ *
+ * .. code-block:: c
+ * KUNIT_STUBBABLE int real_func(int n)
+ * {
+ * pr_info("real_func() called with %d", n);
+ * return 0;
+ * }
+ *
+ * void replacement_func(int n)
+ * {
+ * pr_info("replacement_func() called with %d", n);
+ * return 42;
+ * }
+ *
+ * void example_test(struct kunit *test)
+ * {
+ * kunit_active_ftrace_stub(test, real_func, replacement_func);
+ * KUNIT_EXPECT_EQ(test, real_func(1), 42);
+ * }
+ *
+ */
+#define kunit_activate_ftrace_stub(test, func, replacement) do { \
+ typecheck(typeof(func), replacement); \
+ __kunit_activate_ftrace_stub(test, #func, func, replacement); \
+} while (0)
+
+void __kunit_activate_ftrace_stub(struct kunit *test,
+ const char *name,
+ void *real_fn_addr,
+ void *replacement_addr);
+
+
+void kunit_deactivate_ftrace_stub(struct kunit *test, void *real_fn_addr);
+#endif /* _KUNIT_STUB_H */
diff --git a/lib/kunit/Kconfig b/lib/kunit/Kconfig
index 0b5dfb001bac..978e4f72bae0 100644
--- a/lib/kunit/Kconfig
+++ b/lib/kunit/Kconfig
@@ -59,4 +59,15 @@ config KUNIT_ALL_TESTS
If unsure, say N.
+config KUNIT_FTRACE_STUBS
+ bool "Support for stubbing out functions in KUnit tests with ftrace and kernel livepatch"
+ depends on FTRACE=y && FUNCTION_TRACER=y && MODULES=y && DEBUG_KERNEL=y && KALLSYMS_ALL=y && LIVEPATCH=y
+ help
+ Builds support for stubbing out functions for the duration of KUnit
+ test cases or suites using ftrace and kernel livepatch.
+ See KUNIT_EXAMPLE_TEST for an example.
+
+ NOTE: this does not work on all architectures (like UML, arm64) and
+ relies on a lot of magic (see the dependencies list).
+
endif # KUNIT
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index f9e929700782..75092c12c3d0 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -19,3 +19,7 @@ obj-$(CONFIG_KUNIT_TEST) += string-stream-test.o
endif
obj-$(CONFIG_KUNIT_EXAMPLE_TEST) += kunit-example-test.o
+
+ifeq ($(CONFIG_KUNIT_FTRACE_STUBS),y)
+kunit-objs += ftrace_stub.o
+endif
diff --git a/lib/kunit/ftrace_stub.c b/lib/kunit/ftrace_stub.c
new file mode 100644
index 000000000000..13207e1c7aff
--- /dev/null
+++ b/lib/kunit/ftrace_stub.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <kunit/test.h>
+
+#include <linux/typecheck.h>
+
+#include <linux/ftrace.h>
+#include <linux/livepatch.h>
+#include <linux/sched.h>
+
+struct kunit_ftrace_stub_ctx {
+ struct kunit *test;
+ unsigned long real_fn_addr; /* used as a key to lookup the stub */
+ unsigned long replacement_addr;
+ struct ftrace_ops ops; /* a copy of kunit_stub_base_ops with .private set */
+};
+
+static void kunit_stub_trampoline(unsigned long ip, unsigned long parent_ip,
+ struct ftrace_ops *ops,
+ struct ftrace_regs *fregs)
+{
+ struct kunit_ftrace_stub_ctx *ctx = ops->private;
+ int lock_bit;
+
+ if (current->kunit_test != ctx->test)
+ return;
+
+ lock_bit = ftrace_test_recursion_trylock(ip, parent_ip);
+ KUNIT_ASSERT_GE(ctx->test, lock_bit, 0);
+
+ klp_arch_set_pc(fregs, ctx->replacement_addr);
+
+ ftrace_test_recursion_unlock(lock_bit);
+}
+
+static struct ftrace_ops kunit_stub_base_ops = {
+ .func = &kunit_stub_trampoline,
+ .flags = FTRACE_OPS_FL_IPMODIFY |
+#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
+ FTRACE_OPS_FL_SAVE_REGS |
+#endif
+ FTRACE_OPS_FL_DYNAMIC
+};
+
+static void __kunit_ftrace_stub_resource_free(struct kunit_resource *res)
+{
+ struct kunit_ftrace_stub_ctx *ctx = res->data;
+
+ unregister_ftrace_function(&ctx->ops);
+ kfree(ctx);
+}
+
+/* Matching function for kunit_find_resource(). match_data is real_fn_addr. */
+static bool __kunit_static_stub_resource_match(struct kunit *test,
+ struct kunit_resource *res,
+ void *match_real_fn_addr)
+{
+ /* This pointer is only valid if res is a static stub resource. */
+ struct kunit_ftrace_stub_ctx *ctx = res->data;
+
+ /* Make sure the resource is a static stub resource. */
+ if (res->free != &__kunit_ftrace_stub_resource_free)
+ return false;
+
+ return ctx->real_fn_addr == (unsigned long)match_real_fn_addr;
+}
+
+void kunit_deactivate_ftrace_stub(struct kunit *test, void *real_fn_addr)
+{
+ struct kunit_resource *res;
+
+ KUNIT_ASSERT_PTR_NE_MSG(test, real_fn_addr, NULL,
+ "Tried to deactivate a NULL stub.");
+
+ /* Look up the existing stub for this function. */
+ res = kunit_find_resource(test,
+ __kunit_static_stub_resource_match,
+ real_fn_addr);
+
+ /* Error out if the stub doesn't exist. */
+ KUNIT_ASSERT_PTR_NE_MSG(test, res, NULL,
+ "Tried to deactivate a nonexistent stub.");
+
+ /* Free the stub. We 'put' twice, as we got a reference
+ * from kunit_find_resource(). The free function will deactivate the
+ * ftrace stub.
+ */
+ kunit_remove_resource(test, res);
+ kunit_put_resource(res);
+}
+EXPORT_SYMBOL_GPL(kunit_deactivate_ftrace_stub);
+
+void __kunit_activate_ftrace_stub(struct kunit *test,
+ const char *name,
+ void *real_fn_addr,
+ void *replacement_addr)
+{
+ unsigned long ftrace_ip;
+ struct kunit_ftrace_stub_ctx *ctx;
+ int ret;
+
+ ftrace_ip = ftrace_location((unsigned long)real_fn_addr);
+ if (!ftrace_ip)
+ KUNIT_ASSERT_FAILURE(test, "%s ip is invalid: not a function, or is marked notrace or inline", name);
+
+ /* Allocate the stub context, which contains pointers to the replacement
+ * function and the test object. It's also registered as a KUnit
+ * resource which can be looked up by address (to deactivate manually)
+ * and is destroyed automatically on test exit.
+ */
+ ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
+ KUNIT_ASSERT_NOT_ERR_OR_NULL_MSG(test, ctx, "failed to allocate kunit stub for %s", name);
+
+ ctx->test = test;
+ ctx->ops = kunit_stub_base_ops;
+ ctx->ops.private = ctx;
+ ctx->real_fn_addr = (unsigned long)real_fn_addr;
+ ctx->replacement_addr = (unsigned long)replacement_addr;
+
+ ret = ftrace_set_filter_ip(&ctx->ops, ftrace_ip, 0, 0);
+ if (ret) {
+ kfree(ctx);
+ KUNIT_ASSERT_FAILURE(test, "failed to set filter ip for %s: %d", name, ret);
+ }
+
+ ret = register_ftrace_function(&ctx->ops);
+ if (ret) {
+ kfree(ctx);
+ if (ret == -EBUSY)
+ KUNIT_ASSERT_FAILURE(test, "failed to register stub (-EBUSY) for %s, likely due to already stubbing it?", name);
+ KUNIT_ASSERT_FAILURE(test, "failed to register stub for %s: %d", name, ret);
+ }
+
+ /* Register the stub as a resource with a cleanup function */
+ kunit_alloc_resource(test, NULL,
+ __kunit_ftrace_stub_resource_free,
+ GFP_KERNEL, ctx);
+}
+EXPORT_SYMBOL_GPL(__kunit_activate_ftrace_stub);
diff --git a/lib/kunit/kunit-example-test.c b/lib/kunit/kunit-example-test.c
index 670c21e74446..7f20b132343b 100644
--- a/lib/kunit/kunit-example-test.c
+++ b/lib/kunit/kunit-example-test.c
@@ -8,6 +8,7 @@
#include <kunit/test.h>
#include <kunit/static_stub.h>
+#include <kunit/ftrace_stub.h>
/*
* This is the most fundamental element of KUnit, the test case. A test case
@@ -72,7 +73,7 @@ static void example_mark_skipped_test(struct kunit *test)
}
/* This is a function we'll replace with static stubs. */
-static int add_one(int i)
+static KUNIT_STUBBABLE int add_one(int i)
{
/* This will trigger the stub if active. */
KUNIT_STATIC_STUB_REDIRECT(add_one, i);
@@ -107,6 +108,29 @@ static void example_static_stub_test(struct kunit *test)
KUNIT_EXPECT_EQ(test, add_one(1), 2);
}
+/*
+ * This test shows the use of static stubs.
+ */
+static void example_ftrace_stub_test(struct kunit *test)
+{
+#if !IS_ENABLED(CONFIG_KUNIT_FTRACE_STUBS)
+ kunit_skip(test, "KUNIT_FTRACE_STUBS not enabled");
+#else
+ /* By default, function is not stubbed. */
+ KUNIT_EXPECT_EQ(test, add_one(1), 2);
+
+ /* Replace add_one() with subtract_one(). */
+ kunit_activate_ftrace_stub(test, add_one, subtract_one);
+
+ /* add_one() is now replaced. */
+ KUNIT_EXPECT_EQ(test, add_one(1), 0);
+
+ /* Return add_one() to normal. */
+ kunit_deactivate_ftrace_stub(test, add_one);
+ KUNIT_EXPECT_EQ(test, add_one(1), 2);
+#endif
+}
+
/*
* Here we make a list of all the test cases we want to add to the test suite
* below.
@@ -122,6 +146,7 @@ static struct kunit_case example_test_cases[] = {
KUNIT_CASE(example_skip_test),
KUNIT_CASE(example_mark_skipped_test),
KUNIT_CASE(example_static_stub_test),
+ KUNIT_CASE(example_ftrace_stub_test),
{}
};
diff --git a/lib/kunit/stubs_example.kunitconfig b/lib/kunit/stubs_example.kunitconfig
new file mode 100644
index 000000000000..a47369199fb9
--- /dev/null
+++ b/lib/kunit/stubs_example.kunitconfig
@@ -0,0 +1,11 @@
+CONFIG_KUNIT=y
+CONFIG_KUNIT_FTRACE_STUBS=y
+CONFIG_KUNIT_EXAMPLE_TEST=y
+
+# Depedencies
+CONFIG_FTRACE=y
+CONFIG_FUNCTION_TRACER=y
+CONFIG_MODULES=y
+CONFIG_DEBUG_KERNEL=y
+CONFIG_KALLSYMS_ALL=y
+CONFIG_LIVEPATCH=y
--
2.35.1.894.gb6a874cedc-goog
+Steve Muckle
On Thu, Mar 17, 2022 at 10:13 PM David Gow <[email protected]> wrote:
>
> From: Daniel Latypov <[email protected]>
>
> Allow function redirection using ftrace and kernel livepatch. This is
> basically equivalent to the static_stub support in the previous patch,
> but does not require the function being replaced to be modified (save
> for the addition of KUNIT_STUBBABLE/noinline).
>
> This is hidden behind the CONFIG_KUNIT_FTRACE_STUBS option, and has a
> number of dependencies, including ftrace, livepatch and
> CONFIG_KALLSYMS_ALL. As a result, it only works on architectures where
> these are available.
>
> You can run the KUnit example tests with the following:
> $ ./tools/testing/kunit/kunit.py run --kunitconfig lib/kunit/stubs_example.kunitconfig --arch=x86_64
>
> To the end user, replacing a function is very simple, e.g.
> KUNIT_STUBBABLE void real_func(int n);
> void replacement_func(int n);
>
> /* in tests */
> kunit_activate_ftrace_stub(test, real_func, replacement_func);
>
> The implementation is inspired by Steven's snippet here [1].
>
> Some more details:
> * stubbing is automatically undone at the end of tests
> * it can also be manually undone with kunit_deactive_ftrace_stub()
> * stubbing only applies when current->kunit_test == test
> * note: currently can't have more than one test running at a time
> * KUNIT_STUBBABLE marks tests as noinline when CONFIG_KUNIT_STUBS is set
> * this ensures we can actually stub all calls
> * KUNIT_STUBBABLE_TRAMPOLINE is a version that evaluates to
> __always_inline when stubbing is not enabled
> * This may need to be used with a wrapper function.
> * See the doc comment for more details.
>
> Sharp-edges:
> * kernel livepatch only works on some arches (not UML)
> * if you don't use noinline/KUNIT_STUBBABLE, functions might be inlined
> and thus none of this works:
> * if it's always inlined, at least the attempt to stub will fail
> * if it's sometimes inlined, then the stub silently won't work
>
> [1] https://lore.kernel.org/lkml/[email protected]
>
> Co-developed-by: David Gow <[email protected]>
> Signed-off-by: David Gow <[email protected]>
> Signed-off-by: Daniel Latypov <[email protected]>
> ---
> include/kunit/ftrace_stub.h | 84 +++++++++++++++++
> lib/kunit/Kconfig | 11 +++
> lib/kunit/Makefile | 4 +
> lib/kunit/ftrace_stub.c | 138 ++++++++++++++++++++++++++++
> lib/kunit/kunit-example-test.c | 27 +++++-
> lib/kunit/stubs_example.kunitconfig | 11 +++
> 6 files changed, 274 insertions(+), 1 deletion(-)
> create mode 100644 include/kunit/ftrace_stub.h
> create mode 100644 lib/kunit/ftrace_stub.c
> create mode 100644 lib/kunit/stubs_example.kunitconfig
>
> diff --git a/include/kunit/ftrace_stub.h b/include/kunit/ftrace_stub.h
> new file mode 100644
> index 000000000000..54c053b7e9c1
> --- /dev/null
> +++ b/include/kunit/ftrace_stub.h
> @@ -0,0 +1,84 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _KUNIT_FTRACE_STUB_H
> +#define _KUNIT_FTRACE_STUB_H
> +
> +/** KUNIT_STUBBABLE - marks a function as stubbable when stubbing support is
> + * enabled.
> + *
> + * Stubbing uses ftrace internally, so we can only stub out functions when they
> + * are not inlined. This macro eavlautes to noinline when stubbing support is
> + * enabled to thus make it safe.
> + *
> + * If you cannot add this annotation to the function, you can instead use
> + * KUNIT_STUBBABLE_TRAMPOLINE, which is the same, but evaluates to
> + * __always_inline when stubbing is not enabled.
> + *
> + * Consider copy_to_user, which is marked as __always_inline:
> + *
> + * .. code-block:: c
> + * static KUNIT_STUBBABLE_TRAMPOLINE unsigned long
> + * copy_to_user_trampoline(void __user *to, const void *from, unsigned long n)
> + * {
> + * return copy_to_user(to, from, n);
> + * }
> + *
> + * Then we simply need to update our code to go through this function instead
> + * (in the places where we want to stub it out).
> + */
> +#if IS_ENABLED(CONFIG_KUNIT_FTRACE_STUBS)
> +#define KUNIT_STUBBABLE noinline
> +#define KUNIT_STUBBABLE_TRAMPOLINE noinline
> +#else
> +#define KUNIT_STUBBABLE
> +#define KUNIT_STUBBABLE_TRAMPOLINE __always_inline
> +#endif
> +
> +struct kunit;
> +
> +/**
> + * kunit_activate_ftrace_stub() - makes all calls to @func go to @replacement during @test.
> + * @test: The test context object.
> + * @func: The function to stub out, must be annotated with KUNIT_STUBBABLE.
> + * @replacement: The function to replace @func with.
> + *
> + * All calls to @func will instead call @replacement for the duration of the
> + * current test. If called from outside the test's thread, the function will
> + * not be redirected.
> + *
> + * The redirection can be disabled again with kunit_deactivate_ftrace_stub().
> + *
> + * Example:
> + *
> + * .. code-block:: c
> + * KUNIT_STUBBABLE int real_func(int n)
> + * {
> + * pr_info("real_func() called with %d", n);
> + * return 0;
> + * }
> + *
> + * void replacement_func(int n)
> + * {
> + * pr_info("replacement_func() called with %d", n);
> + * return 42;
> + * }
> + *
> + * void example_test(struct kunit *test)
> + * {
> + * kunit_active_ftrace_stub(test, real_func, replacement_func);
> + * KUNIT_EXPECT_EQ(test, real_func(1), 42);
> + * }
> + *
> + */
> +#define kunit_activate_ftrace_stub(test, func, replacement) do { \
> + typecheck(typeof(func), replacement); \
> + __kunit_activate_ftrace_stub(test, #func, func, replacement); \
> +} while (0)
> +
> +void __kunit_activate_ftrace_stub(struct kunit *test,
> + const char *name,
> + void *real_fn_addr,
> + void *replacement_addr);
> +
> +
> +void kunit_deactivate_ftrace_stub(struct kunit *test, void *real_fn_addr);
> +#endif /* _KUNIT_STUB_H */
> diff --git a/lib/kunit/Kconfig b/lib/kunit/Kconfig
> index 0b5dfb001bac..978e4f72bae0 100644
> --- a/lib/kunit/Kconfig
> +++ b/lib/kunit/Kconfig
> @@ -59,4 +59,15 @@ config KUNIT_ALL_TESTS
>
> If unsure, say N.
>
> +config KUNIT_FTRACE_STUBS
> + bool "Support for stubbing out functions in KUnit tests with ftrace and kernel livepatch"
> + depends on FTRACE=y && FUNCTION_TRACER=y && MODULES=y && DEBUG_KERNEL=y && KALLSYMS_ALL=y && LIVEPATCH=y
> + help
> + Builds support for stubbing out functions for the duration of KUnit
> + test cases or suites using ftrace and kernel livepatch.
> + See KUNIT_EXAMPLE_TEST for an example.
> +
> + NOTE: this does not work on all architectures (like UML, arm64) and
> + relies on a lot of magic (see the dependencies list).
> +
> endif # KUNIT
> diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> index f9e929700782..75092c12c3d0 100644
> --- a/lib/kunit/Makefile
> +++ b/lib/kunit/Makefile
> @@ -19,3 +19,7 @@ obj-$(CONFIG_KUNIT_TEST) += string-stream-test.o
> endif
>
> obj-$(CONFIG_KUNIT_EXAMPLE_TEST) += kunit-example-test.o
> +
> +ifeq ($(CONFIG_KUNIT_FTRACE_STUBS),y)
> +kunit-objs += ftrace_stub.o
> +endif
> diff --git a/lib/kunit/ftrace_stub.c b/lib/kunit/ftrace_stub.c
> new file mode 100644
> index 000000000000..13207e1c7aff
> --- /dev/null
> +++ b/lib/kunit/ftrace_stub.c
> @@ -0,0 +1,138 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <kunit/test.h>
> +
> +#include <linux/typecheck.h>
> +
> +#include <linux/ftrace.h>
> +#include <linux/livepatch.h>
> +#include <linux/sched.h>
> +
> +struct kunit_ftrace_stub_ctx {
> + struct kunit *test;
> + unsigned long real_fn_addr; /* used as a key to lookup the stub */
> + unsigned long replacement_addr;
> + struct ftrace_ops ops; /* a copy of kunit_stub_base_ops with .private set */
> +};
> +
> +static void kunit_stub_trampoline(unsigned long ip, unsigned long parent_ip,
> + struct ftrace_ops *ops,
> + struct ftrace_regs *fregs)
> +{
> + struct kunit_ftrace_stub_ctx *ctx = ops->private;
> + int lock_bit;
> +
> + if (current->kunit_test != ctx->test)
> + return;
> +
> + lock_bit = ftrace_test_recursion_trylock(ip, parent_ip);
> + KUNIT_ASSERT_GE(ctx->test, lock_bit, 0);
> +
> + klp_arch_set_pc(fregs, ctx->replacement_addr);
> +
> + ftrace_test_recursion_unlock(lock_bit);
> +}
> +
> +static struct ftrace_ops kunit_stub_base_ops = {
> + .func = &kunit_stub_trampoline,
> + .flags = FTRACE_OPS_FL_IPMODIFY |
> +#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> + FTRACE_OPS_FL_SAVE_REGS |
> +#endif
> + FTRACE_OPS_FL_DYNAMIC
> +};
> +
> +static void __kunit_ftrace_stub_resource_free(struct kunit_resource *res)
> +{
> + struct kunit_ftrace_stub_ctx *ctx = res->data;
> +
> + unregister_ftrace_function(&ctx->ops);
> + kfree(ctx);
> +}
> +
> +/* Matching function for kunit_find_resource(). match_data is real_fn_addr. */
> +static bool __kunit_static_stub_resource_match(struct kunit *test,
> + struct kunit_resource *res,
> + void *match_real_fn_addr)
> +{
> + /* This pointer is only valid if res is a static stub resource. */
> + struct kunit_ftrace_stub_ctx *ctx = res->data;
> +
> + /* Make sure the resource is a static stub resource. */
> + if (res->free != &__kunit_ftrace_stub_resource_free)
> + return false;
> +
> + return ctx->real_fn_addr == (unsigned long)match_real_fn_addr;
> +}
> +
> +void kunit_deactivate_ftrace_stub(struct kunit *test, void *real_fn_addr)
> +{
> + struct kunit_resource *res;
> +
> + KUNIT_ASSERT_PTR_NE_MSG(test, real_fn_addr, NULL,
> + "Tried to deactivate a NULL stub.");
> +
> + /* Look up the existing stub for this function. */
> + res = kunit_find_resource(test,
> + __kunit_static_stub_resource_match,
> + real_fn_addr);
> +
> + /* Error out if the stub doesn't exist. */
> + KUNIT_ASSERT_PTR_NE_MSG(test, res, NULL,
> + "Tried to deactivate a nonexistent stub.");
> +
> + /* Free the stub. We 'put' twice, as we got a reference
> + * from kunit_find_resource(). The free function will deactivate the
> + * ftrace stub.
> + */
> + kunit_remove_resource(test, res);
> + kunit_put_resource(res);
> +}
> +EXPORT_SYMBOL_GPL(kunit_deactivate_ftrace_stub);
> +
> +void __kunit_activate_ftrace_stub(struct kunit *test,
> + const char *name,
> + void *real_fn_addr,
> + void *replacement_addr)
> +{
> + unsigned long ftrace_ip;
> + struct kunit_ftrace_stub_ctx *ctx;
> + int ret;
> +
> + ftrace_ip = ftrace_location((unsigned long)real_fn_addr);
> + if (!ftrace_ip)
> + KUNIT_ASSERT_FAILURE(test, "%s ip is invalid: not a function, or is marked notrace or inline", name);
> +
> + /* Allocate the stub context, which contains pointers to the replacement
> + * function and the test object. It's also registered as a KUnit
> + * resource which can be looked up by address (to deactivate manually)
> + * and is destroyed automatically on test exit.
> + */
> + ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
> + KUNIT_ASSERT_NOT_ERR_OR_NULL_MSG(test, ctx, "failed to allocate kunit stub for %s", name);
> +
> + ctx->test = test;
> + ctx->ops = kunit_stub_base_ops;
> + ctx->ops.private = ctx;
> + ctx->real_fn_addr = (unsigned long)real_fn_addr;
> + ctx->replacement_addr = (unsigned long)replacement_addr;
> +
> + ret = ftrace_set_filter_ip(&ctx->ops, ftrace_ip, 0, 0);
> + if (ret) {
> + kfree(ctx);
> + KUNIT_ASSERT_FAILURE(test, "failed to set filter ip for %s: %d", name, ret);
> + }
> +
> + ret = register_ftrace_function(&ctx->ops);
> + if (ret) {
> + kfree(ctx);
> + if (ret == -EBUSY)
> + KUNIT_ASSERT_FAILURE(test, "failed to register stub (-EBUSY) for %s, likely due to already stubbing it?", name);
> + KUNIT_ASSERT_FAILURE(test, "failed to register stub for %s: %d", name, ret);
> + }
> +
> + /* Register the stub as a resource with a cleanup function */
> + kunit_alloc_resource(test, NULL,
> + __kunit_ftrace_stub_resource_free,
> + GFP_KERNEL, ctx);
> +}
> +EXPORT_SYMBOL_GPL(__kunit_activate_ftrace_stub);
> diff --git a/lib/kunit/kunit-example-test.c b/lib/kunit/kunit-example-test.c
> index 670c21e74446..7f20b132343b 100644
> --- a/lib/kunit/kunit-example-test.c
> +++ b/lib/kunit/kunit-example-test.c
> @@ -8,6 +8,7 @@
>
> #include <kunit/test.h>
> #include <kunit/static_stub.h>
> +#include <kunit/ftrace_stub.h>
>
> /*
> * This is the most fundamental element of KUnit, the test case. A test case
> @@ -72,7 +73,7 @@ static void example_mark_skipped_test(struct kunit *test)
> }
>
> /* This is a function we'll replace with static stubs. */
> -static int add_one(int i)
> +static KUNIT_STUBBABLE int add_one(int i)
> {
> /* This will trigger the stub if active. */
> KUNIT_STATIC_STUB_REDIRECT(add_one, i);
> @@ -107,6 +108,29 @@ static void example_static_stub_test(struct kunit *test)
> KUNIT_EXPECT_EQ(test, add_one(1), 2);
> }
>
> +/*
> + * This test shows the use of static stubs.
> + */
> +static void example_ftrace_stub_test(struct kunit *test)
> +{
> +#if !IS_ENABLED(CONFIG_KUNIT_FTRACE_STUBS)
> + kunit_skip(test, "KUNIT_FTRACE_STUBS not enabled");
> +#else
> + /* By default, function is not stubbed. */
> + KUNIT_EXPECT_EQ(test, add_one(1), 2);
> +
> + /* Replace add_one() with subtract_one(). */
> + kunit_activate_ftrace_stub(test, add_one, subtract_one);
> +
> + /* add_one() is now replaced. */
> + KUNIT_EXPECT_EQ(test, add_one(1), 0);
> +
> + /* Return add_one() to normal. */
> + kunit_deactivate_ftrace_stub(test, add_one);
> + KUNIT_EXPECT_EQ(test, add_one(1), 2);
> +#endif
> +}
> +
> /*
> * Here we make a list of all the test cases we want to add to the test suite
> * below.
> @@ -122,6 +146,7 @@ static struct kunit_case example_test_cases[] = {
> KUNIT_CASE(example_skip_test),
> KUNIT_CASE(example_mark_skipped_test),
> KUNIT_CASE(example_static_stub_test),
> + KUNIT_CASE(example_ftrace_stub_test),
> {}
> };
>
> diff --git a/lib/kunit/stubs_example.kunitconfig b/lib/kunit/stubs_example.kunitconfig
> new file mode 100644
> index 000000000000..a47369199fb9
> --- /dev/null
> +++ b/lib/kunit/stubs_example.kunitconfig
> @@ -0,0 +1,11 @@
> +CONFIG_KUNIT=y
> +CONFIG_KUNIT_FTRACE_STUBS=y
> +CONFIG_KUNIT_EXAMPLE_TEST=y
> +
> +# Depedencies
> +CONFIG_FTRACE=y
> +CONFIG_FUNCTION_TRACER=y
> +CONFIG_MODULES=y
> +CONFIG_DEBUG_KERNEL=y
> +CONFIG_KALLSYMS_ALL=y
> +CONFIG_LIVEPATCH=y
> --
> 2.35.1.894.gb6a874cedc-goog
>
On Thu, Mar 17, 2022 at 9:13 PM David Gow <[email protected]> wrote:
> +
> +/** KUNIT_STUBBABLE - marks a function as stubbable when stubbing support is
> + * enabled.
> + *
> + * Stubbing uses ftrace internally, so we can only stub out functions when they
> + * are not inlined. This macro eavlautes to noinline when stubbing support is
Just noting a couple typos lest they be forgotten:
*evaluates
> + * enabled to thus make it safe.
> + *
<snip>
> + *
> + * void replacement_func(int n)
> + * {
> + * pr_info("replacement_func() called with %d", n);
> + * return 42;
> + * }
> + *
> + * void example_test(struct kunit *test)
> + * {
> + * kunit_active_ftrace_stub(test, real_func, replacement_func);
*activate