+Steve Muckle
On Thu, Mar 17, 2022 at 10:13 PM David Gow davidgow@google.com wrote:
From: Daniel Latypov dlatypov@google.com
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/20220224091550.2b7e8784@gandalf.local.home
Co-developed-by: David Gow davidgow@google.com Signed-off-by: David Gow davidgow@google.com Signed-off-by: Daniel Latypov dlatypov@google.com
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=yhelpBuilds support for stubbing out functions for the duration of KUnittest 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) andrelies 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