From patchwork Sat Sep 10 21:28:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Gow X-Patchwork-Id: 604695 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 56965C6FA82 for ; Sat, 10 Sep 2022 21:35:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230142AbiIJVf1 (ORCPT ); Sat, 10 Sep 2022 17:35:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42396 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230257AbiIJVfJ (ORCPT ); Sat, 10 Sep 2022 17:35:09 -0400 Received: from mail-pj1-x1049.google.com (mail-pj1-x1049.google.com [IPv6:2607:f8b0:4864:20::1049]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CC286451 for ; Sat, 10 Sep 2022 14:29:45 -0700 (PDT) Received: by mail-pj1-x1049.google.com with SMTP id 2-20020a17090a0b8200b001fdb8fd5f29so2444890pjr.8 for ; Sat, 10 Sep 2022 14:29:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date; bh=AQSKyyxRM/1kBel8Rm51NXzepcXl8uNiWvzYLoszy5E=; b=n8OGXovB5FHB+F5y6rDvwNqMdhfVoc1TSoNm0hOcpRnXTtlPzq2bayYdR+A9cMdZio KzyfVxHd48bdOQBiBR6VMQl/YshnLy4Nt08kEGf4tXpgHmJKz0kji3szP+cs4QEY/7T5 vMMTXKIaMxuGLG8F+Qvxn6bEgP54oMvFXngPhfAJC61y8MvABZ8TN8OInHiGys5UqzmD ZJkC11cu/9/nAL7vaiOOGl+kPhcDxwLB0+81dPY9BNES9qz0IM4Ffoz1siCz4I/uOQ4+ 2Lr5zelrdp3ZS9ZJ/fc4e2RAgEkSusp+mb3plWyFIvnCafW5NRMYRRQhPa+ky2lZBVyA NjzA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date; bh=AQSKyyxRM/1kBel8Rm51NXzepcXl8uNiWvzYLoszy5E=; b=DOvCvi6mVhn+a6dYLM7PZ2bu6As+nxgryp+FTsCOPu1ddgbvVAIpGDyn3ylHESoHLa wezt4veD19EWFa1HZ5Y2kY9mhNQ3ie3KhYqks+bvHh6zycrtvJFZe8dihAJfZ5Y383O9 hBNCbKu7XgrG7Ygc7Y2cwFnYEs/GRB6SDdFtGE3NHBc3G1vPgMRTgkGGIacaQFGf2L2b mlyDcpmBVJqbZnL3F9TZ7DATNzLQLxlczZQTOaMlWgrhbyuStyWNzpUwPKxAgProHi2c 1dRhqvH3JpAwAFOYy9RBcz5MjmCMCFMrvWxaCxyt3la9VRqcCfFp61nqKdi1r3ibd3BE N4LQ== X-Gm-Message-State: ACgBeo3JuaHqns9eUqBpcsfJvHvuDp88V0WDpZHArPqfu0sZSC2kpFvf expZq6zem1zKx4zFevHcGG4fI2z5cnj6iA== X-Google-Smtp-Source: AA6agR5UOnOMtfBD2Sy2mmTQLFHHhyx4dWygs7y/DUkF0UU+Tvj4ZAiQ9ZW9GNd+yLu6S9cS/z5liRDBLG640w== X-Received: from slicestar.c.googlers.com ([fda3:e722:ac3:cc00:4f:4b78:c0a8:20a1]) (user=davidgow job=sendgmr) by 2002:a17:902:7602:b0:172:a064:4a2f with SMTP id k2-20020a170902760200b00172a0644a2fmr19529716pll.56.1662845303343; Sat, 10 Sep 2022 14:28:23 -0700 (PDT) Date: Sun, 11 Sep 2022 05:28:03 +0800 In-Reply-To: <20220910212804.670622-1-davidgow@google.com> Mime-Version: 1.0 References: <20220910212804.670622-1-davidgow@google.com> X-Mailer: git-send-email 2.37.2.789.g6183377224-goog Message-ID: <20220910212804.670622-2-davidgow@google.com> Subject: [RFC PATCH v2 1/2] kunit: Expose 'static stub' API to redirect functions From: David Gow To: Brendan Higgins , Daniel Latypov , Kees Cook , Shuah Khan , Steven Rostedt , Joe Fradley Cc: Steve Muckle , kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, David Gow Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Add a simple way of redirecting calls to functions by including a special prologue in the "real" function which checks to see if the replacement function should be called (and, if so, calls it). To redirect calls to a function, make the first (non-declaration) line of the function: KUNIT_STATIC_STUB_REDIRECT(function_name, [function arguments]); (This will compile away to nothing if KUnit is not enabled, otherwise it will check if a redirection is active, call the replacement function, and return.) Calls to the real function can be redirected to a replacement using: kunit_activate_static_stub(test, real_fn, replacement_fn); The redirection will only affect calls made from within the kthread of the current test, and will be automatically disabled when the test completes. It can also be manually disabled with kunit_deactivate_static_stub(). The 'example' KUnit test suite has a more complete example. This is intended to be an alternative to ftrace-based stubbing (see the next patch), with different tradeoffs. In particular: - 'static stubs' work on all architectures, and don't have any dependencies. - There's no separate Kconfig option to enable them, they always exist. - They must be explicitly opted-into by the function being replaced (which can be good or bad depending on your POV) - They have a greater performance penalty when not in active use (as every call to the real function must check to see if the stub is enabled) - They could more easily be extended to pass additional context to replacement functions. Co-developed-by: Daniel Latypov Signed-off-by: Daniel Latypov Signed-off-by: David Gow --- Changes since RFC v1: https://lore.kernel.org/lkml/20220318021314.3225240-2-davidgow@google.com/ - Use typecheck_fn() to fix typechecking in some cases (thanks Brendan) --- include/kunit/static_stub.h | 106 ++++++++++++++++++++++++++++ lib/kunit/Makefile | 1 + lib/kunit/kunit-example-test.c | 38 ++++++++++ lib/kunit/static_stub.c | 125 +++++++++++++++++++++++++++++++++ 4 files changed, 270 insertions(+) create mode 100644 include/kunit/static_stub.h create mode 100644 lib/kunit/static_stub.c diff --git a/include/kunit/static_stub.h b/include/kunit/static_stub.h new file mode 100644 index 000000000000..7417ba8efdbb --- /dev/null +++ b/include/kunit/static_stub.h @@ -0,0 +1,106 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * KUnit function redirection (static stubbing) API. + * + * Copyright (C) 2022, Google LLC. + * Author: David Gow + */ +#ifndef _KUNIT_STATIC_STUB_H +#define _KUNIT_STATIC_STUB_H + +#if !IS_REACHABLE(CONFIG_KUNIT) + +/* If CONFIG_KUNIT is not enabled, these stubs quietly disappear. */ +#define KUNIT_TRIGGER_STATIC_STUB(real_fn_name, args...) do {} while (0) + +#else + +#include + +#include /* for {un,}likely() */ +#include /* for task_struct */ + +/* Returns the address of the replacement function. */ +void *__kunit_get_static_stub_address(struct kunit *test, void *real_fn_addr); + +/** + * KUNIT_STATIC_STUB_REDIRECT() - call a replacement 'static stub' if one exists + * @real_fn_name: The name of this function (as an identifier, not a string) + * @args: All of the arguments passed to this function + * + * This is a function prologue which is used to allow calls to the current + * function to be redirected by a KUnit test. KUnit tests can call + * kunit_activate_static_stub() to pass a replacement function in. The + * replacement function will be called by KUNIT_TRIGGER_STATIC_STUB(), which + * will then return from the function. If the caller is not in a KUnit context, + * the function will continue execution as normal. + * + * Example: + * + * .. code-block:: c + * int real_func(int n) + * { + * KUNIT_STATIC_STUB_REDIRECT(real_func, n); + * return 0; + * } + * + * void replacement_func(int n) + * { + * return 42; + * } + * + * void example_test(struct kunit *test) + * { + * kunit_activate_static_stub(test, real_func, replacement_func); + * KUNIT_EXPECT_EQ(test, real_func(1), 42); + * } + * + */ +#define KUNIT_STATIC_STUB_REDIRECT(real_fn_name, args...) \ +do { \ + typeof(&real_fn_name) replacement; \ + struct kunit *current_test = current->kunit_test; \ + \ + if (likely(!current_test)) \ + break; \ + \ + KUNIT_ASSERT_STREQ_MSG(current_test, __func__, #real_fn_name, \ + "Static stub function name mismatch"); \ + \ + replacement = __kunit_get_static_stub_address(current_test, \ + &real_fn_name); \ + \ + if (unlikely(replacement)) \ + return replacement(args); \ +} while (0) + +/* Helper function for kunit_activate_static_stub(). The macro does + * typechecking, so use it instead. + */ +void __kunit_activate_static_stub(struct kunit *test, + void *real_fn_addr, + void *replacement_addr); + +/** + * kunit_activate_static_stub() - replace a function using static stubs. + * @test: A pointer to the 'struct kunit' test context for the current test. + * @real_fn_addr: The address of the function to replace. + * @replacement_addr: The address of the function to replace it with. + * + * When activated, calls to real_fn_addr from within this test (even if called + * indirectly) will instead call replacement_addr. The function pointed to by + * real_fn_addr must begin with the static stub prologue in + * KUNIT_TRIGGER_STATIC_STUB() for this to work. real_fn_addr and + * replacement_addr must have the same type. + * + * The redirection can be disabled again with kunit_deactivate_static_stub(). + */ +#define kunit_activate_static_stub(test, real_fn_addr, replacement_addr) do { \ + typecheck_fn(typeof(&real_fn_addr), replacement_addr); \ + __kunit_activate_static_stub(test, real_fn_addr, replacement_addr); \ +} while (0) + +void kunit_deactivate_static_stub(struct kunit *test, void *real_fn_addr); + +#endif +#endif diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile index 29aff6562b42..78d9d3414b67 100644 --- a/lib/kunit/Makefile +++ b/lib/kunit/Makefile @@ -2,6 +2,7 @@ obj-$(CONFIG_KUNIT) += kunit.o kunit-objs += test.o \ resource.o \ + static_stub.o \ string-stream.o \ assert.o \ try-catch.o \ diff --git a/lib/kunit/kunit-example-test.c b/lib/kunit/kunit-example-test.c index f8fe582c9e36..a065dd0ae332 100644 --- a/lib/kunit/kunit-example-test.c +++ b/lib/kunit/kunit-example-test.c @@ -7,6 +7,7 @@ */ #include +#include /* * This is the most fundamental element of KUnit, the test case. A test case @@ -123,6 +124,42 @@ static void example_all_expect_macros_test(struct kunit *test) KUNIT_ASSERT_GT_MSG(test, sizeof(int), 0, "Your ints are 0-bit?!"); } +/* This is a function we'll replace with static stubs. */ +static int add_one(int i) +{ + /* This will trigger the stub if active. */ + KUNIT_STATIC_STUB_REDIRECT(add_one, i); + + return i + 1; +} + +/* This is used as a replacement for the above function. */ +static int subtract_one(int i) +{ + /* We don't need to trigger the stub from the replacement. */ + + return i - 1; +} + +/* + * This test shows the use of static stubs. + */ +static void example_static_stub_test(struct kunit *test) +{ + /* By default, function is not stubbed. */ + KUNIT_EXPECT_EQ(test, add_one(1), 2); + + /* Replace add_one() with subtract_one(). */ + kunit_activate_static_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_static_stub(test, add_one); + KUNIT_EXPECT_EQ(test, add_one(1), 2); +} + /* * Here we make a list of all the test cases we want to add to the test suite * below. @@ -138,6 +175,7 @@ static struct kunit_case example_test_cases[] = { KUNIT_CASE(example_skip_test), KUNIT_CASE(example_mark_skipped_test), KUNIT_CASE(example_all_expect_macros_test), + KUNIT_CASE(example_static_stub_test), {} }; diff --git a/lib/kunit/static_stub.c b/lib/kunit/static_stub.c new file mode 100644 index 000000000000..b06b88f82dd7 --- /dev/null +++ b/lib/kunit/static_stub.c @@ -0,0 +1,125 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * KUnit function redirection (static stubbing) API. + * + * Copyright (C) 2022, Google LLC. + * Author: David Gow + */ + +#include +#include + + +/* Context for a static stub. This is stored in the resource data. */ +struct kunit_static_stub_ctx { + void *real_fn_addr; + void *replacement_addr; +}; + +static void __kunit_static_stub_resource_free(struct kunit_resource *res) +{ + kfree(res->data); +} + +/* 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_static_stub_ctx *ctx = res->data; + + /* Make sure the resource is a static stub resource. */ + if (res->free != &__kunit_static_stub_resource_free) + return false; + + return ctx->real_fn_addr == match_real_fn_addr; +} + +/* Returns the address of the replacement function. */ +void *__kunit_get_static_stub_address(struct kunit *test, void *real_fn_addr) +{ + struct kunit_resource *res; + struct kunit_static_stub_ctx *ctx; + void *replacement_addr; + + res = kunit_find_resource(test, + __kunit_static_stub_resource_match, + real_fn_addr); + + if (!res) + return NULL; + + ctx = res->data; + replacement_addr = ctx->replacement_addr; + kunit_put_resource(res); + return replacement_addr; +} +EXPORT_SYMBOL_GPL(__kunit_get_static_stub_address); + +void kunit_deactivate_static_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() + */ + kunit_remove_resource(test, res); + kunit_put_resource(res); +} +EXPORT_SYMBOL_GPL(kunit_deactivate_static_stub); + +/* Helper function for kunit_activate_static_stub(). The macro does + * typechecking, so use it instead. + */ +void __kunit_activate_static_stub(struct kunit *test, + void *real_fn_addr, + void *replacement_addr) +{ + struct kunit_static_stub_ctx *ctx; + struct kunit_resource *res; + + KUNIT_ASSERT_PTR_NE_MSG(test, real_fn_addr, NULL, + "Tried to activate a stub for function NULL"); + + /* If the replacement address is NULL, deactivate the stub. */ + if (!replacement_addr) { + kunit_deactivate_static_stub(test, replacement_addr); + return; + } + + /* Look up any existing stubs for this function, and replace them. */ + res = kunit_find_resource(test, + __kunit_static_stub_resource_match, + real_fn_addr); + if (res) { + ctx = res->data; + ctx->replacement_addr = replacement_addr; + + /* We got an extra reference from find_resource(), so put it. */ + kunit_put_resource(res); + } else { + ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx); + ctx->real_fn_addr = real_fn_addr; + ctx->replacement_addr = replacement_addr; + res = kunit_alloc_resource(test, NULL, + &__kunit_static_stub_resource_free, + GFP_KERNEL, ctx); + } +} +EXPORT_SYMBOL_GPL(__kunit_activate_static_stub); + + From patchwork Sat Sep 10 21:28:04 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Gow X-Patchwork-Id: 605640 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AEA7FC6FA83 for ; Sat, 10 Sep 2022 21:35:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230365AbiIJVfd (ORCPT ); Sat, 10 Sep 2022 17:35:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49830 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230376AbiIJVfN (ORCPT ); Sat, 10 Sep 2022 17:35:13 -0400 Received: from mail-pj1-x104a.google.com (mail-pj1-x104a.google.com [IPv6:2607:f8b0:4864:20::104a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5D26721833 for ; Sat, 10 Sep 2022 14:29:48 -0700 (PDT) Received: by mail-pj1-x104a.google.com with SMTP id oo12-20020a17090b1c8c00b001faa0b549caso5326078pjb.0 for ; Sat, 10 Sep 2022 14:29:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date; bh=xYhC/vunqIspNGc0NjaBaZxphwujM9X3N3qa94aFOOY=; b=kFLhvsZXp82eWLX3OanDPllrIADP4hUNwMJCnO2TCZPT0PdspByeUUv+o45BU32UdQ PfhHg2uC0c5ALOTbNRJUyRjmc4P7H4EvuUUjzV+9bp6njF6KWUsv5Y19zHNJgymAjtNf F+UDMAK7vPuRjbZ26Kv/WhN4cUZTb0Nd3F65ihHXI56L9G52nhyZdgX+1ICkcfZkOJBG 75ZgqoHNuz7aPGQ/i+dFXSvpeiiFwU7RfclHIP9QUztmGVjQ2dfqnZpHNmCaFsd0uipw Jei6Jnqrzy9dHGkg6fMFhf1LvR+YMeiK3itwBoa5/Glk4AbACfx4hkfThLHgbqbhe/uZ mG+Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date; bh=xYhC/vunqIspNGc0NjaBaZxphwujM9X3N3qa94aFOOY=; b=LjHOzD1oOGyPhl29h3TNITLcJi4ZzSCoLXQW0ZZxp+SwL2l9ug1vYD8pSnYV7eoXrM Dw4VRWy/7Pu6Z8/BN3ejveujV/quRfQ9zrLWQDGJcCDnk3dKVrJtif9cj+xY1Lr5YPgv NRhzeRIkUBi24GmqbYbejGfhgRDzruSzkQPxr9WPl1lCnSmCW1EJXY8dZ1uiO4pcmII6 0rja7SKWnfguZBP8QuH5hYirpEg51ylb/Vsek4jLWLprpKFv/96vUb5dgOvnwau3gpzq iJRS+/6gxlBbXISOdM7J9L6guHoem5KR6uiKppn4IVfl+Hg9SNQp0C69bYjZRFWI5jtV IkEQ== X-Gm-Message-State: ACgBeo1FJaXlo9JrnTv/Em4toNIfIx4nJ7FhkEj4m3kqQThq7o6j4Z9p 0yH2FQ6MYW4u8E8bzyss1UAxkv1bwPlIvg== X-Google-Smtp-Source: AA6agR4plFoX0c5CNTARiKFERZf7iQc5ahU33NT0TREPvvRx3YogHXysMCsPRcD3Ev5/8H1Kz2I5TPGzLG1nHw== X-Received: from slicestar.c.googlers.com ([fda3:e722:ac3:cc00:4f:4b78:c0a8:20a1]) (user=davidgow job=sendgmr) by 2002:a05:6a00:13aa:b0:540:dc91:83df with SMTP id t42-20020a056a0013aa00b00540dc9183dfmr10357642pfg.5.1662845307884; Sat, 10 Sep 2022 14:28:27 -0700 (PDT) Date: Sun, 11 Sep 2022 05:28:04 +0800 In-Reply-To: <20220910212804.670622-1-davidgow@google.com> Mime-Version: 1.0 References: <20220910212804.670622-1-davidgow@google.com> X-Mailer: git-send-email 2.37.2.789.g6183377224-goog Message-ID: <20220910212804.670622-3-davidgow@google.com> Subject: [RFC PATCH v2 2/2] kunit: expose ftrace-based API for stubbing out functions during tests From: David Gow To: Brendan Higgins , Daniel Latypov , Kees Cook , Shuah Khan , Steven Rostedt , Joe Fradley Cc: Steve Muckle , kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, David Gow Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org From: Daniel Latypov 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 ftrace only works on some arches (not UML) * and (this use of it) seems broken on others (e.g, arm64) * 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 Signed-off-by: David Gow Signed-off-by: Daniel Latypov Reviewed-by: Steven Rostedt (Google) --- Changes since RFC v1: https://lore.kernel.org/lkml/20220318021314.3225240-3-davidgow@google.com/ - Fix some typos (thanks Daniel) - Use typecheck_fn() to fix typechecking in some cases (thanks Brendan) - Use ftrace_instruction_pointer_set() in place of kernel livepatch, which seems to have disappeared: https://lore.kernel.org/lkml/0a76550d-008d-0364-8244-4dae2981ea05@csgroup.eu/T/ - Fix a copy-paste name error in the resource finding function. - Rebase on top of torvalds/master, as it wasn't applying cleanly. --- include/kunit/ftrace_stub.h | 84 +++++++++++++++++ lib/kunit/Kconfig | 11 +++ lib/kunit/Makefile | 4 + lib/kunit/ftrace_stub.c | 137 ++++++++++++++++++++++++++++ lib/kunit/kunit-example-test.c | 27 +++++- lib/kunit/stubs_example.kunitconfig | 10 ++ 6 files changed, 272 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..82d33267f49f --- /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 evalautes 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_activate_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_fn(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..35462529dd30 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 + 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 78d9d3414b67..f2421b388108 100644 --- a/lib/kunit/Makefile +++ b/lib/kunit/Makefile @@ -20,3 +20,7 @@ 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..7386340e8dd7 --- /dev/null +++ b/lib/kunit/ftrace_stub.c @@ -0,0 +1,137 @@ +// SPDX-License-Identifier: GPL-2.0 +#include + +#include + +#include +#include + +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_instruction_pointer_set(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_ftrace_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_ftrace_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 a065dd0ae332..c61d366192d8 100644 --- a/lib/kunit/kunit-example-test.c +++ b/lib/kunit/kunit-example-test.c @@ -8,6 +8,7 @@ #include #include +#include /* * This is the most fundamental element of KUnit, the test case. A test case @@ -125,7 +126,7 @@ 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); @@ -160,6 +161,29 @@ 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. @@ -176,6 +200,7 @@ static struct kunit_case example_test_cases[] = { KUNIT_CASE(example_mark_skipped_test), KUNIT_CASE(example_all_expect_macros_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..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