Allow function redirection using ftrace. 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 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/20220224091550.2b7e8784@gandalf.local.home
Co-developed-by: Daniel Latypov dlatypov@google.com Signed-off-by: Eddie Phillips eddiephillips@google.com ---
Link to original: https://lore.kernel.org/all/20220910212804.670622-3-davidgow@google.com/
include/kunit/ftrace_stub.h | 84 ++++++++++++++++ lib/kunit/Kconfig | 11 +++ lib/kunit/Makefile | 4 + lib/kunit/ftrace_stub.c | 146 ++++++++++++++++++++++++++++ lib/kunit/kunit-example-test.c | 29 +++++- lib/kunit/stubs_example.kunitconfig | 10 ++ 6 files changed, 282 insertions(+), 2 deletions(-) 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..bfd57ea6289c --- /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, real_fn_addr, replacement_addr) do { \ + typecheck_fn(typeof(&replacement_addr), real_fn_addr); \ + __kunit_activate_ftrace_stub(test, #real_fn_addr, real_fn_addr, replacement_addr); \ +} 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 7a6af361d2fc..8a629017b917 100644 --- a/lib/kunit/Kconfig +++ b/lib/kunit/Kconfig @@ -70,6 +70,17 @@ 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 + help + Builds support for stubbing out functions for the duration of KUnit + test cases or suites using ftrace. + See KUNIT_EXAMPLE_TEST for an example. + + NOTE: this does not work on all architectures (like UML) and + relies on a lot of magic (see the dependencies list). + config KUNIT_DEFAULT_ENABLED bool "Default value of kunit.enable" default y diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile index 656f1fa35abc..f04f6ea4d6a8 100644 --- a/lib/kunit/Makefile +++ b/lib/kunit/Makefile @@ -29,3 +29,7 @@ obj-$(CONFIG_KUNIT_TEST) += assert_test.o endif
obj-$(CONFIG_KUNIT_EXAMPLE_TEST) += kunit-example-test.o + +ifeq ($(CONFIG_KUNIT_FTRACE_STUBS),y) +kunit-objs += ftrace_stub.o +endif \ No newline at end of file diff --git a/lib/kunit/ftrace_stub.c b/lib/kunit/ftrace_stub.c new file mode 100644 index 000000000000..b19eaa35f5ed --- /dev/null +++ b/lib/kunit/ftrace_stub.c @@ -0,0 +1,146 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <kunit/ftrace_stub.h> +#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); + + ftrace_regs_set_instruction_pointer(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_FAIL_ASSERTION(test, KUNIT_ASSERTION, + "%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_PTR_NE_MSG(test, ctx, NULL, "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_FAIL_ASSERTION(test, KUNIT_ASSERTION, + "failed to set filter ip for %s: %d", name, ret); + } + + ret = register_ftrace_function(&ctx->ops); + if (ret) { + kfree(ctx); + if (ret == -EBUSY) + KUNIT_FAIL_ASSERTION( + test, KUNIT_ASSERTION, + "failed to register stub (-EBUSY) for %s, likely due to already stubbing it?", + name); + KUNIT_FAIL_ASSERTION(test, KUNIT_ASSERTION, + "failed to register stub for %s: %d", name, + ret); + } + + 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 9452b163956f..676ad552ae7b 100644 --- a/lib/kunit/kunit-example-test.c +++ b/lib/kunit/kunit-example-test.c @@ -6,8 +6,9 @@ * Author: Brendan Higgins brendanhiggins@google.com */
-#include <kunit/test.h> +#include <kunit/ftrace_stub.h> #include <kunit/static_stub.h> +#include <kunit/test.h>
/* * This is the most fundamental element of KUnit, the test case. A test case @@ -152,7 +153,7 @@ static void example_all_expect_macros_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); @@ -221,6 +222,29 @@ static void example_static_stub_using_fn_ptr_test(struct kunit *test) KUNIT_EXPECT_EQ(test, add_one(1), 2); }
+/* + * This test shows the use of dynamic 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 +} + static const struct example_param { int value; } example_params_array[] = { @@ -506,6 +530,7 @@ static struct kunit_case example_test_cases[] = { KUNIT_CASE(example_all_expect_macros_test), KUNIT_CASE(example_static_stub_test), KUNIT_CASE(example_static_stub_using_fn_ptr_test), + KUNIT_CASE(example_ftrace_stub_test), KUNIT_CASE(example_priv_test), KUNIT_CASE_PARAM(example_params_test, example_gen_params), KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init, kunit_array_gen_params, diff --git a/lib/kunit/stubs_example.kunitconfig b/lib/kunit/stubs_example.kunitconfig new file mode 100644 index 000000000000..20af4da9bc75 --- /dev/null +++ b/lib/kunit/stubs_example.kunitconfig @@ -0,0 +1,10 @@ +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