Re: [PATCH v4 25/45] kmsan: add tests for KMSAN

Marco Elver
2022-07-12T14:17:26Z

)

On Fri, 1 Jul 2022 at 16:24, 'Alexander Potapenko' via kasan-dev
<kasan-dev@googlegroups.com> wrote:
>
> The testing module triggers KMSAN warnings in different cases and checks
> that the errors are properly reported, using console probes to capture
> the tool's output.
>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> ---
> v2:
> -- add memcpy tests
>
> v4:
> -- change sizeof(type) to sizeof(*ptr)
> -- add test expectations for CONFIG_KMSAN_CHECK_PARAM_RETVAL
>
> Link: https://linux-review.googlesource.com/id/I49c3f59014cc37fd13541c80beb0b75a75244650
> ---
> lib/Kconfig.kmsan | 12 +
> mm/kmsan/Makefile | 4 +
> mm/kmsan/kmsan_test.c | 552 ++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 568 insertions(+)
> create mode 100644 mm/kmsan/kmsan_test.c
>
> diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> index 8f768d4034e3c..f56ed7f7c7090 100644
> --- a/lib/Kconfig.kmsan
> +++ b/lib/Kconfig.kmsan
> @@ -47,4 +47,16 @@ config KMSAN_CHECK_PARAM_RETVAL
> may potentially report errors in corner cases when non-instrumented
> functions call instrumented ones.
>
> +config KMSAN_KUNIT_TEST
> + tristate "KMSAN integration test suite" if !KUNIT_ALL_TESTS
> + default KUNIT_ALL_TESTS
> + depends on TRACEPOINTS && KUNIT
> + help
> + Test suite for KMSAN, testing various error detection scenarios,
> + and checking that reports are correctly output to console.
> +
> + Say Y here if you want the test to be built into the kernel and run
> + during boot; say M if you want the test to build as a module; say N
> + if you are unsure.
> +
> endif
> diff --git a/mm/kmsan/Makefile b/mm/kmsan/Makefile
> index 401acb1a491ce..98eab2856626f 100644
> --- a/mm/kmsan/Makefile
> +++ b/mm/kmsan/Makefile
> @@ -22,3 +22,7 @@ CFLAGS_init.o := $(CC_FLAGS_KMSAN_RUNTIME)
> CFLAGS_instrumentation.o := $(CC_FLAGS_KMSAN_RUNTIME)
> CFLAGS_report.o := $(CC_FLAGS_KMSAN_RUNTIME)
> CFLAGS_shadow.o := $(CC_FLAGS_KMSAN_RUNTIME)
> +
> +obj-$(CONFIG_KMSAN_KUNIT_TEST) += kmsan_test.o
> +KMSAN_SANITIZE_kmsan_test.o := y
> +CFLAGS_kmsan_test.o += $(call cc-disable-warning, uninitialized)
> diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
> new file mode 100644
> index 0000000000000..1b8da71ae0d4f
> --- /dev/null
> +++ b/mm/kmsan/kmsan_test.c
> @@ -0,0 +1,552 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Test cases for KMSAN.
> + * For each test case checks the presence (or absence) of generated reports.
> + * Relies on 'console' tracepoint to capture reports as they appear in the
> + * kernel log.
> + *
> + * Copyright (C) 2021-2022, Google LLC.
> + * Author: Alexander Potapenko <glider@google.com>
> + *
> + */
> +
> +#include <kunit/test.h>
> +#include "kmsan.h"
> +
> +#include <linux/jiffies.h>
> +#include <linux/kernel.h>
> +#include <linux/kmsan.h>
> +#include <linux/mm.h>
> +#include <linux/random.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/string.h>
> +#include <linux/tracepoint.h>
> +#include <trace/events/printk.h>
> +
> +static DEFINE_PER_CPU(int, per_cpu_var);
> +
> +/* Report as observed from console. */
> +static struct {
> + spinlock_t lock;
> + bool available;
> + bool ignore; /* Stop console output collection. */
> + char header[256];
> +} observed = {
> + .lock = __SPIN_LOCK_UNLOCKED(observed.lock),
> +};
> +
> +/* Probe for console output: obtains observed lines of interest. */
> +static void probe_console(void *ignore, const char *buf, size_t len)
> +{
> + unsigned long flags;
> +
> + if (observed.ignore)
> + return;
> + spin_lock_irqsave(&observed.lock, flags);
> +
> + if (strnstr(buf, "BUG: KMSAN: ", len)) {
> + /*
> + * KMSAN report and related to the test.
> + *
> + * The provided @buf is not NUL-terminated; copy no more than
> + * @len bytes and let strscpy() add the missing NUL-terminator.
> + */
> + strscpy(observed.header, buf,
> + min(len + 1, sizeof(observed.header)));
> + WRITE_ONCE(observed.available, true);
> + observed.ignore = true;
> + }
> + spin_unlock_irqrestore(&observed.lock, flags);
> +}
> +
> +/* Check if a report related to the test exists. */
> +static bool report_available(void)
> +{
> + return READ_ONCE(observed.available);
> +}
> +
> +/* Information we expect in a report. */
> +struct expect_report {
> + const char *error_type; /* Error type. */
> + /*
> + * Kernel symbol from the error header, or NULL if no report is
> + * expected.
> + */
> + const char *symbol;
> +};
> +
> +/* Check observed report matches information in @r. */
> +static bool report_matches(const struct expect_report *r)
> +{
> + typeof(observed.header) expected_header;
> + unsigned long flags;
> + bool ret = false;
> + const char *end;
> + char *cur;
> +
> + /* Doubled-checked locking. */
> + if (!report_available() || !r->symbol)
> + return (!report_available() && !r->symbol);
> +
> + /* Generate expected report contents. */
> +
> + /* Title */
> + cur = expected_header;
> + end = &expected_header[sizeof(expected_header) - 1];
> +
> + cur += scnprintf(cur, end - cur, "BUG: KMSAN: %s", r->error_type);
> +
> + scnprintf(cur, end - cur, " in %s", r->symbol);
> + /* The exact offset won't match, remove it; also strip module name. */
> + cur = strchr(expected_header, '+');
> + if (cur)
> + *cur = '\0';
> +
> + spin_lock_irqsave(&observed.lock, flags);
> + if (!report_available())
> + goto out; /* A new report is being captured. */
> +
> + /* Finally match expected output to what we actually observed. */
> + ret = strstr(observed.header, expected_header);
> +out:
> + spin_unlock_irqrestore(&observed.lock, flags);
> +
> + return ret;
> +}
> +
> +/* ===== Test cases ===== */
> +
> +/* Prevent replacing branch with select in LLVM. */
> +static noinline void check_true(char *arg)
> +{
> + pr_info("%s is true\n", arg);
> +}
> +
> +static noinline void check_false(char *arg)
> +{
> + pr_info("%s is false\n", arg);
> +}
> +
> +#define USE(x) \
> + do { \
> + if (x) \
> + check_true(#x); \
> + else \
> + check_false(#x); \
> + } while (0)
> +
> +#define EXPECTATION_ETYPE_FN(e, reason, fn) \
> + struct expect_report e = { \
> + .error_type = reason, \
> + .symbol = fn, \
> + }
> +
> +#define EXPECTATION_NO_REPORT(e) EXPECTATION_ETYPE_FN(e, NULL, NULL)
> +#define EXPECTATION_UNINIT_VALUE_FN(e, fn) \
> + EXPECTATION_ETYPE_FN(e, "uninit-value", fn)
> +#define EXPECTATION_UNINIT_VALUE(e) EXPECTATION_UNINIT_VALUE_FN(e, __func__)
> +#define EXPECTATION_USE_AFTER_FREE(e) \
> + EXPECTATION_ETYPE_FN(e, "use-after-free", __func__)
> +
> +/* Test case: ensure that kmalloc() returns uninitialized memory. */
> +static void test_uninit_kmalloc(struct kunit *test)
> +{
> + EXPECTATION_UNINIT_VALUE(expect);
> + int *ptr;
> +
> + kunit_info(test, "uninitialized kmalloc test (UMR report)\n");
> + ptr = kmalloc(sizeof(*ptr), GFP_KERNEL);
> + USE(*ptr);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/*
> + * Test case: ensure that kmalloc'ed memory becomes initialized after memset().
> + */
> +static void test_init_kmalloc(struct kunit *test)
> +{
> + EXPECTATION_NO_REPORT(expect);
> + int *ptr;
> +
> + kunit_info(test, "initialized kmalloc test (no reports)\n");
> + ptr = kmalloc(sizeof(*ptr), GFP_KERNEL);
> + memset(ptr, 0, sizeof(*ptr));
> + USE(*ptr);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/* Test case: ensure that kzalloc() returns initialized memory. */
> +static void test_init_kzalloc(struct kunit *test)
> +{
> + EXPECTATION_NO_REPORT(expect);
> + int *ptr;
> +
> + kunit_info(test, "initialized kzalloc test (no reports)\n");
> + ptr = kzalloc(sizeof(*ptr), GFP_KERNEL);
> + USE(*ptr);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/* Test case: ensure that local variables are uninitialized by default. */
> +static void test_uninit_stack_var(struct kunit *test)
> +{
> + EXPECTATION_UNINIT_VALUE(expect);
> + volatile int cond;
> +
> + kunit_info(test, "uninitialized stack variable (UMR report)\n");
> + USE(cond);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/* Test case: ensure that local variables with initializers are initialized. */
> +static void test_init_stack_var(struct kunit *test)
> +{
> + EXPECTATION_NO_REPORT(expect);
> + volatile int cond = 1;
> +
> + kunit_info(test, "initialized stack variable (no reports)\n");
> + USE(cond);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +static noinline void two_param_fn_2(int arg1, int arg2)
> +{
> + USE(arg1);
> + USE(arg2);
> +}
> +
> +static noinline void one_param_fn(int arg)
> +{
> + two_param_fn_2(arg, arg);
> + USE(arg);
> +}
> +
> +static noinline void two_param_fn(int arg1, int arg2)
> +{
> + int init = 0;
> +
> + one_param_fn(init);
> + USE(arg1);
> + USE(arg2);
> +}
> +
> +static void test_params(struct kunit *test)
> +{
> +#ifdef CONFIG_KMSAN_CHECK_PARAM_RETVAL

if (IS_ENABLED(...))

> + /*
> + * With eager param/retval checking enabled, KMSAN will report an error
> + * before the call to two_param_fn().
> + */
> + EXPECTATION_UNINIT_VALUE_FN(expect, "test_params");
> +#else
> + EXPECTATION_UNINIT_VALUE_FN(expect, "two_param_fn");
> +#endif
> + volatile int uninit, init = 1;
> +
> + kunit_info(test,
> + "uninit passed through a function parameter (UMR report)\n");
> + two_param_fn(uninit, init);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +static int signed_sum3(int a, int b, int c)
> +{
> + return a + b + c;
> +}
> +
> +/*
> + * Test case: ensure that uninitialized values are tracked through function
> + * arguments.
> + */
> +static void test_uninit_multiple_params(struct kunit *test)
> +{
> + EXPECTATION_UNINIT_VALUE(expect);
> + volatile char b = 3, c;
> + volatile int a;
> +
> + kunit_info(test, "uninitialized local passed to fn (UMR report)\n");
> + USE(signed_sum3(a, b, c));
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/* Helper function to make an array uninitialized. */
> +static noinline void do_uninit_local_array(char *array, int start, int stop)
> +{
> + volatile char uninit;
> + int i;
> +
> + for (i = start; i < stop; i++)
> + array[i] = uninit;
> +}
> +
> +/*
> + * Test case: ensure kmsan_check_memory() reports an error when checking
> + * uninitialized memory.
> + */
> +static void test_uninit_kmsan_check_memory(struct kunit *test)
> +{
> + EXPECTATION_UNINIT_VALUE_FN(expect, "test_uninit_kmsan_check_memory");
> + volatile char local_array[8];
> +
> + kunit_info(
> + test,
> + "kmsan_check_memory() called on uninit local (UMR report)\n");
> + do_uninit_local_array((char *)local_array, 5, 7);
> +
> + kmsan_check_memory((char *)local_array, 8);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/*
> + * Test case: check that a virtual memory range created with vmap() from
> + * initialized pages is still considered as initialized.
> + */
> +static void test_init_kmsan_vmap_vunmap(struct kunit *test)
> +{
> + EXPECTATION_NO_REPORT(expect);
> + const int npages = 2;
> + struct page **pages;
> + void *vbuf;
> + int i;
> +
> + kunit_info(test, "pages initialized via vmap (no reports)\n");
> +
> + pages = kmalloc_array(npages, sizeof(*pages), GFP_KERNEL);
> + for (i = 0; i < npages; i++)
> + pages[i] = alloc_page(GFP_KERNEL);
> + vbuf = vmap(pages, npages, VM_MAP, PAGE_KERNEL);
> + memset(vbuf, 0xfe, npages * PAGE_SIZE);
> + for (i = 0; i < npages; i++)
> + kmsan_check_memory(page_address(pages[i]), PAGE_SIZE);
> +
> + if (vbuf)
> + vunmap(vbuf);
> + for (i = 0; i < npages; i++)

add { }

> + if (pages[i])
> + __free_page(pages[i]);
> + kfree(pages);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/*
> + * Test case: ensure that memset() can initialize a buffer allocated via
> + * vmalloc().
> + */
> +static void test_init_vmalloc(struct kunit *test)
> +{
> + EXPECTATION_NO_REPORT(expect);
> + int npages = 8, i;
> + char *buf;
> +
> + kunit_info(test, "vmalloc buffer can be initialized (no reports)\n");
> + buf = vmalloc(PAGE_SIZE * npages);
> + buf[0] = 1;
> + memset(buf, 0xfe, PAGE_SIZE * npages);
> + USE(buf[0]);
> + for (i = 0; i < npages; i++)
> + kmsan_check_memory(&buf[PAGE_SIZE * i], PAGE_SIZE);
> + vfree(buf);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/* Test case: ensure that use-after-free reporting works. */
> +static void test_uaf(struct kunit *test)
> +{
> + EXPECTATION_USE_AFTER_FREE(expect);
> + volatile int value;
> + volatile int *var;
> +
> + kunit_info(test, "use-after-free in kmalloc-ed buffer (UMR report)\n");
> + var = kmalloc(80, GFP_KERNEL);
> + var[3] = 0xfeedface;
> + kfree((int *)var);
> + /* Copy the invalid value before checking it. */
> + value = var[3];
> + USE(value);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/*
> + * Test case: ensure that uninitialized values are propagated through per-CPU
> + * memory.
> + */
> +static void test_percpu_propagate(struct kunit *test)
> +{
> + EXPECTATION_UNINIT_VALUE(expect);
> + volatile int uninit, check;
> +
> + kunit_info(test,
> + "uninit local stored to per_cpu memory (UMR report)\n");
> +
> + this_cpu_write(per_cpu_var, uninit);
> + check = this_cpu_read(per_cpu_var);
> + USE(check);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/*
> + * Test case: ensure that passing uninitialized values to printk() leads to an
> + * error report.
> + */
> +static void test_printk(struct kunit *test)
> +{
> +#ifdef CONFIG_KMSAN_CHECK_PARAM_RETVAL

if (IS_ENABLED(CONFIG_KMSAN_CHECK_PARAM_RETVAL))

> + /*
> + * With eager param/retval checking enabled, KMSAN will report an error
> + * before the call to pr_info().
> + */
> + EXPECTATION_UNINIT_VALUE_FN(expect, "test_printk");
> +#else
> + EXPECTATION_UNINIT_VALUE_FN(expect, "number");
> +#endif
> + volatile int uninit;
> +
> + kunit_info(test, "uninit local passed to pr_info() (UMR report)\n");
> + pr_info("%px contains %d\n", &uninit, uninit);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/*
> + * Test case: ensure that memcpy() correctly copies uninitialized values between
> + * aligned `src` and `dst`.
> + */
> +static void test_memcpy_aligned_to_aligned(struct kunit *test)
> +{
> + EXPECTATION_UNINIT_VALUE_FN(expect, "test_memcpy_aligned_to_aligned");
> + volatile int uninit_src;
> + volatile int dst = 0;
> +
> + kunit_info(test, "memcpy()ing aligned uninit src to aligned dst (UMR report)\n");
> + memcpy((void *)&dst, (void *)&uninit_src, sizeof(uninit_src));
> + kmsan_check_memory((void *)&dst, sizeof(dst));
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/*
> + * Test case: ensure that memcpy() correctly copies uninitialized values between
> + * aligned `src` and unaligned `dst`.
> + *
> + * Copying aligned 4-byte value to an unaligned one leads to touching two
> + * aligned 4-byte values. This test case checks that KMSAN correctly reports an
> + * error on the first of the two values.
> + */
> +static void test_memcpy_aligned_to_unaligned(struct kunit *test)
> +{
> + EXPECTATION_UNINIT_VALUE_FN(expect, "test_memcpy_aligned_to_unaligned");
> + volatile int uninit_src;
> + volatile char dst[8] = {0};
> +
> + kunit_info(test, "memcpy()ing aligned uninit src to unaligned dst (UMR report)\n");
> + memcpy((void *)&dst[1], (void *)&uninit_src, sizeof(uninit_src));
> + kmsan_check_memory((void *)dst, 4);
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +/*
> + * Test case: ensure that memcpy() correctly copies uninitialized values between
> + * aligned `src` and unaligned `dst`.
> + *
> + * Copying aligned 4-byte value to an unaligned one leads to touching two
> + * aligned 4-byte values. This test case checks that KMSAN correctly reports an
> + * error on the second of the two values.
> + */
> +static void test_memcpy_aligned_to_unaligned2(struct kunit *test)
> +{
> + EXPECTATION_UNINIT_VALUE_FN(expect, "test_memcpy_aligned_to_unaligned2");
> + volatile int uninit_src;
> + volatile char dst[8] = {0};
> +
> + kunit_info(test, "memcpy()ing aligned uninit src to unaligned dst - part 2 (UMR report)\n");
> + memcpy((void *)&dst[1], (void *)&uninit_src, sizeof(uninit_src));
> + kmsan_check_memory((void *)&dst[4], sizeof(uninit_src));
> + KUNIT_EXPECT_TRUE(test, report_matches(&expect));
> +}
> +
> +static struct kunit_case kmsan_test_cases[] = {
> + KUNIT_CASE(test_uninit_kmalloc),
> + KUNIT_CASE(test_init_kmalloc),
> + KUNIT_CASE(test_init_kzalloc),
> + KUNIT_CASE(test_uninit_stack_var),
> + KUNIT_CASE(test_init_stack_var),
> + KUNIT_CASE(test_params),
> + KUNIT_CASE(test_uninit_multiple_params),
> + KUNIT_CASE(test_uninit_kmsan_check_memory),
> + KUNIT_CASE(test_init_kmsan_vmap_vunmap),
> + KUNIT_CASE(test_init_vmalloc),
> + KUNIT_CASE(test_uaf),
> + KUNIT_CASE(test_percpu_propagate),
> + KUNIT_CASE(test_printk),
> + KUNIT_CASE(test_memcpy_aligned_to_aligned),
> + KUNIT_CASE(test_memcpy_aligned_to_unaligned),
> + KUNIT_CASE(test_memcpy_aligned_to_unaligned2),
> + {},
> +};
> +
> +/* ===== End test cases ===== */
> +
> +static int test_init(struct kunit *test)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&observed.lock, flags);
> + observed.header[0] = '\0';
> + observed.ignore = false;
> + observed.available = false;
> + spin_unlock_irqrestore(&observed.lock, flags);
> +
> + return 0;
> +}
> +
> +static void test_exit(struct kunit *test)
> +{
> +}
> +
> +static struct kunit_suite kmsan_test_suite = {
> + .name = "kmsan",
> + .test_cases = kmsan_test_cases,
> + .init = test_init,
> + .exit = test_exit,
> +};
> +static struct kunit_suite *kmsan_test_suites[] = { &kmsan_test_suite, NULL };
> +
> +static void register_tracepoints(struct tracepoint *tp, void *ignore)
> +{
> + check_trace_callback_type_console(probe_console);
> + if (!strcmp(tp->name, "console"))
> + WARN_ON(tracepoint_probe_register(tp, probe_console, NULL));
> +}
> +
> +static void unregister_tracepoints(struct tracepoint *tp, void *ignore)
> +{
> + if (!strcmp(tp->name, "console"))
> + tracepoint_probe_unregister(tp, probe_console, NULL);
> +}
> +
> +/*
> + * We only want to do tracepoints setup and teardown once, therefore we have to
> + * customize the init and exit functions and cannot rely on kunit_test_suite().
> + */

This is no longer true. See a recent version of
mm/kfence/kfence_test.c which uses the new suite_init/exit.

> +static int __init kmsan_test_init(void)
> +{
> + /*
> + * Because we want to be able to build the test as a module, we need to
> + * iterate through all known tracepoints, since the static registration
> + * won't work here.
> + */
> + for_each_kernel_tracepoint(register_tracepoints, NULL);
> + return __kunit_test_suites_init(kmsan_test_suites);
> +}
> +
> +static void kmsan_test_exit(void)
> +{
> + __kunit_test_suites_exit(kmsan_test_suites);
> + for_each_kernel_tracepoint(unregister_tracepoints, NULL);
> + tracepoint_synchronize_unregister();
> +}
> +
> +late_initcall_sync(kmsan_test_init);
> +module_exit(kmsan_test_exit);
> +
> +MODULE_LICENSE("GPL v2");

A recent version of checkpatch should complain about this, wanting
only "GPL" instead of "GPL v2".

> +MODULE_AUTHOR("Alexander Potapenko <glider@google.com>");