kfence: add test suite

Add KFENCE test suite, testing various error detection scenarios. Makes
use of KUnit for test organization. Since KFENCE's interface to obtain
error reports is via the console, the test verifies that KFENCE outputs
expected reports to the console.

[[e-mail]: fix typo in test]
Link: https://lkml.kernel.org/r/[e-mail]
[[e-mail]: show access type in report]
Link: https://lkml.kernel.org/r/[e-mail]

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Alexander Potapenko <[e-mail]>
Signed-off-by: Marco Elver <[e-mail]>
Reviewed-by: Dmitry Vyukov <[e-mail]>
Co-developed-by: Alexander Potapenko <[e-mail]>
Reviewed-by: Jann Horn <[e-mail]>
Cc: Andrey Konovalov <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Christopher Lameter <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Hillf Danton <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Joern Engel <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Paul E. McKenney <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: SeongJae Park <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/dev-tools/kfence.rst

···
 A typical out-of-bounds access looks like this::
 
     ==================================================================
-    BUG: KFENCE: out-of-bounds in test_out_of_bounds_read+0xa3/0x22b
+    BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0xa3/0x22b
 
-    Out-of-bounds access at 0xffffffffb672efff (1B left of kfence-#17):
+    Out-of-bounds read at 0xffffffffb672efff (1B left of kfence-#17):
      test_out_of_bounds_read+0xa3/0x22b
      kunit_try_run_case+0x51/0x85
      kunit_generic_run_threadfn_adapter+0x16/0x30
···
 Use-after-free accesses are reported as::
 
     ==================================================================
-    BUG: KFENCE: use-after-free in test_use_after_free_read+0xb3/0x143
+    BUG: KFENCE: use-after-free read in test_use_after_free_read+0xb3/0x143
 
-    Use-after-free access at 0xffffffffb673dfe0 (in kfence-#24):
+    Use-after-free read at 0xffffffffb673dfe0 (in kfence-#24):
      test_use_after_free_read+0xb3/0x143
      kunit_try_run_case+0x51/0x85
      kunit_generic_run_threadfn_adapter+0x16/0x30
···
 object pages had not yet been allocated::
 
     ==================================================================
-    BUG: KFENCE: invalid access in test_invalid_access+0x26/0xe0
+    BUG: KFENCE: invalid read in test_invalid_access+0x26/0xe0
 
-    Invalid access at 0xffffffffb670b00a:
+    Invalid read at 0xffffffffb670b00a:
      test_invalid_access+0x26/0xe0
      kunit_try_run_case+0x51/0x85
      kunit_generic_run_threadfn_adapter+0x16/0x30

arch/arm64/mm/fault.c

···
 	} else if (addr < PAGE_SIZE) {
 		msg = "NULL pointer dereference";
 	} else {
-		if (kfence_handle_page_fault(addr, regs))
+		if (kfence_handle_page_fault(addr, esr & ESR_ELx_WNR, regs))
 			return;
 
 		msg = "paging request";

arch/x86/mm/fault.c

···
 		efi_crash_gracefully_on_page_fault(address);
 
 	/* Only not-present faults should be handled by KFENCE. */
-	if (!(error_code & X86_PF_PROT) && kfence_handle_page_fault(address, regs))
+	if (!(error_code & X86_PF_PROT) &&
+	    kfence_handle_page_fault(address, error_code & X86_PF_WRITE, regs))
 		return;
 
 oops:

include/linux/kfence.h

···
 /**
  * kfence_handle_page_fault() - perform page fault handling for KFENCE pages
  * @addr: faulting address
+ * @is_write: is access a write
  * @regs: current struct pt_regs (can be NULL, but shows full stack trace)
  *
  * Return:
···
  * cases KFENCE prints an error message and marks the offending page as
  * present, so that the kernel can proceed.
  */
-bool __must_check kfence_handle_page_fault(unsigned long addr, struct pt_regs *regs);
+bool __must_check kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs);
 
 #else /* CONFIG_KFENCE */
 
···
 static inline void *kfence_object_start(const void *addr) { return NULL; }
 static inline void __kfence_free(void *addr) { }
 static inline bool __must_check kfence_free(void *addr) { return false; }
-static inline bool __must_check kfence_handle_page_fault(unsigned long addr, struct pt_regs *regs) { return false; }
+static inline bool __must_check kfence_handle_page_fault(unsigned long addr, bool is_write,
+							 struct pt_regs *regs)
+{
+	return false;
+}
 
 #endif
 

lib/Kconfig.kfence

···
 
 	  Only for KFENCE testing; set to 0 if you are not a KFENCE developer.
 
+config KFENCE_KUNIT_TEST
+	tristate "KFENCE integration test suite" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	depends on TRACEPOINTS && KUNIT
+	help
+	  Test suite for KFENCE, testing various error detection scenarios with
+	  various allocation types, 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 # KFENCE

mm/kfence/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_KFENCE) := core.o report.o
+
+CFLAGS_kfence_test.o := -g -fno-omit-frame-pointer -fno-optimize-sibling-calls
+obj-$(CONFIG_KFENCE_KUNIT_TEST) += kfence_test.o

mm/kfence/core.c

···
 		return true;
 
 	atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
-	kfence_report_error((unsigned long)addr, NULL, addr_to_metadata((unsigned long)addr),
+	kfence_report_error((unsigned long)addr, false, NULL, addr_to_metadata((unsigned long)addr),
 			    KFENCE_ERROR_CORRUPTION);
 	return false;
 }
···
 	if (meta->state != KFENCE_OBJECT_ALLOCATED || meta->addr != (unsigned long)addr) {
 		/* Invalid or double-free, bail out. */
 		atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
-		kfence_report_error((unsigned long)addr, NULL, meta, KFENCE_ERROR_INVALID_FREE);
+		kfence_report_error((unsigned long)addr, false, NULL, meta,
+				    KFENCE_ERROR_INVALID_FREE);
 		raw_spin_unlock_irqrestore(&meta->lock, flags);
 		return;
 	}
···
 		kfence_guarded_free(addr, meta, false);
 }
 
-bool kfence_handle_page_fault(unsigned long addr, struct pt_regs *regs)
+bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs)
 {
 	const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE;
 	struct kfence_metadata *to_report = NULL;
···
 
 out:
 	if (to_report) {
-		kfence_report_error(addr, regs, to_report, error_type);
+		kfence_report_error(addr, is_write, regs, to_report, error_type);
 		raw_spin_unlock_irqrestore(&to_report->lock, flags);
 	} else {
 		/* This may be a UAF or OOB access, but we can't be sure. */
-		kfence_report_error(addr, regs, NULL, KFENCE_ERROR_INVALID);
+		kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID);
 	}
 
 	return kfence_unprotect(addr); /* Unprotect and let access proceed. */

mm/kfence/kfence.h

···
 	KFENCE_ERROR_INVALID_FREE,	/* Invalid free. */
 };
 
-void kfence_report_error(unsigned long address, struct pt_regs *regs,
+void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
 			 const struct kfence_metadata *meta, enum kfence_error_type type);
 
 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);

mm/kfence/kfence_test.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test cases for KFENCE memory safety error detector. Since the interface with
+ * which KFENCE's reports are obtained is via the console, this is the output we
+ * should verify. 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) 2020, Google LLC.
+ * Author: Alexander Potapenko <[e-mail]>
+ *         Marco Elver <[e-mail]>
+ */
+
+#include <kunit/test.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/kfence.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>
+
+#include "kfence.h"
+
+/* Report as observed from console. */
+static struct {
+	spinlock_t lock;
+	int nlines;
+	char lines[2][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;
+	int nlines;
+
+	spin_lock_irqsave(&observed.lock, flags);
+	nlines = observed.nlines;
+
+	if (strnstr(buf, "BUG: KFENCE: ", len) && strnstr(buf, "test_", len)) {
+		/*
+		 * KFENCE 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.lines[0], buf, min(len + 1, sizeof(observed.lines[0])));
+		nlines = 1;
+	} else if (nlines == 1 && (strnstr(buf, "at 0x", len) || strnstr(buf, "of 0x", len))) {
+		strscpy(observed.lines[nlines++], buf, min(len + 1, sizeof(observed.lines[0])));
+	}
+
+	WRITE_ONCE(observed.nlines, nlines); /* Publish new nlines. */
+	spin_unlock_irqrestore(&observed.lock, flags);
+}
+
+/* Check if a report related to the test exists. */
+static bool report_available(void)
+{
+	return READ_ONCE(observed.nlines) == ARRAY_SIZE(observed.lines);
+}
+
+/* Information we expect in a report. */
+struct expect_report {
+	enum kfence_error_type type; /* The type or error. */
+	void *fn; /* Function pointer to expected function where access occurred. */
+	char *addr; /* Address at which the bad access occurred. */
+	bool is_write; /* Is access a write. */
+};
+
+static const char *get_access_type(const struct expect_report *r)
+{
+	return r->is_write ? "write" : "read";
+}
+
+/* Check observed report matches information in @r. */
+static bool report_matches(const struct expect_report *r)
+{
+	bool ret = false;
+	unsigned long flags;
+	typeof(observed.lines) expect;
+	const char *end;
+	char *cur;
+
+	/* Doubled-checked locking. */
+	if (!report_available())
+		return false;
+
+	/* Generate expected report contents. */
+
+	/* Title */
+	cur = expect[0];
+	end = &expect[0][sizeof(expect[0]) - 1];
+	switch (r->type) {
+	case KFENCE_ERROR_OOB:
+		cur += scnprintf(cur, end - cur, "BUG: KFENCE: out-of-bounds %s",
+				 get_access_type(r));
+		break;
+	case KFENCE_ERROR_UAF:
+		cur += scnprintf(cur, end - cur, "BUG: KFENCE: use-after-free %s",
+				 get_access_type(r));
+		break;
+	case KFENCE_ERROR_CORRUPTION:
+		cur += scnprintf(cur, end - cur, "BUG: KFENCE: memory corruption");
+		break;
+	case KFENCE_ERROR_INVALID:
+		cur += scnprintf(cur, end - cur, "BUG: KFENCE: invalid %s",
+				 get_access_type(r));
+		break;
+	case KFENCE_ERROR_INVALID_FREE:
+		cur += scnprintf(cur, end - cur, "BUG: KFENCE: invalid free");
+		break;
+	}
+
+	scnprintf(cur, end - cur, " in %pS", r->fn);
+	/* The exact offset won't match, remove it; also strip module name. */
+	cur = strchr(expect[0], '+');
+	if (cur)
+		*cur = '\0';
+
+	/* Access information */
+	cur = expect[1];
+	end = &expect[1][sizeof(expect[1]) - 1];
+
+	switch (r->type) {
+	case KFENCE_ERROR_OOB:
+		cur += scnprintf(cur, end - cur, "Out-of-bounds %s at", get_access_type(r));
+		break;
+	case KFENCE_ERROR_UAF:
+		cur += scnprintf(cur, end - cur, "Use-after-free %s at", get_access_type(r));
+		break;
+	case KFENCE_ERROR_CORRUPTION:
+		cur += scnprintf(cur, end - cur, "Corrupted memory at");
+		break;
+	case KFENCE_ERROR_INVALID:
+		cur += scnprintf(cur, end - cur, "Invalid %s at", get_access_type(r));
+		break;
+	case KFENCE_ERROR_INVALID_FREE:
+		cur += scnprintf(cur, end - cur, "Invalid free of");
+		break;
+	}
+
+	cur += scnprintf(cur, end - cur, " 0x" PTR_FMT, (void *)r->addr);
+
+	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.lines[0], expect[0]) && strstr(observed.lines[1], expect[1]);
+out:
+	spin_unlock_irqrestore(&observed.lock, flags);
+	return ret;
+}
+
+/* ===== Test cases ===== */
+
+#define TEST_PRIV_WANT_MEMCACHE ((void *)1)
+
+/* Cache used by tests; if NULL, allocate from kmalloc instead. */
+static struct kmem_cache *test_cache;
+
+static size_t setup_test_cache(struct kunit *test, size_t size, slab_flags_t flags,
+			       void (*ctor)(void *))
+{
+	if (test->priv != TEST_PRIV_WANT_MEMCACHE)
+		return size;
+
+	kunit_info(test, "%s: size=%zu, ctor=%ps\n", __func__, size, ctor);
+
+	/*
+	 * Use SLAB_NOLEAKTRACE to prevent merging with existing caches. Any
+	 * other flag in SLAB_NEVER_MERGE also works. Use SLAB_ACCOUNT to
+	 * allocate via memcg, if enabled.
+	 */
+	flags |= SLAB_NOLEAKTRACE | SLAB_ACCOUNT;
+	test_cache = kmem_cache_create("test", size, 1, flags, ctor);
+	KUNIT_ASSERT_TRUE_MSG(test, test_cache, "could not create cache");
+
+	return size;
+}
+
+static void test_cache_destroy(void)
+{
+	if (!test_cache)
+		return;
+
+	kmem_cache_destroy(test_cache);
+	test_cache = NULL;
+}
+
+static inline size_t kmalloc_cache_alignment(size_t size)
+{
+	return kmalloc_caches[kmalloc_type(GFP_KERNEL)][kmalloc_index(size)]->align;
+}
+
+/* Must always inline to match stack trace against caller. */
+static __always_inline void test_free(void *ptr)
+{
+	if (test_cache)
+		kmem_cache_free(test_cache, ptr);
+	else
+		kfree(ptr);
+}
+
+/*
+ * If this should be a KFENCE allocation, and on which side the allocation and
+ * the closest guard page should be.
+ */
+enum allocation_policy {
+	ALLOCATE_ANY, /* KFENCE, any side. */
+	ALLOCATE_LEFT, /* KFENCE, left side of page. */
+	ALLOCATE_RIGHT, /* KFENCE, right side of page. */
+	ALLOCATE_NONE, /* No KFENCE allocation. */
+};
+
+/*
+ * Try to get a guarded allocation from KFENCE. Uses either kmalloc() or the
+ * current test_cache if set up.
+ */
+static void *test_alloc(struct kunit *test, size_t size, gfp_t gfp, enum allocation_policy policy)
+{
+	void *alloc;
+	unsigned long timeout, resched_after;
+	const char *policy_name;
+
+	switch (policy) {
+	case ALLOCATE_ANY:
+		policy_name = "any";
+		break;
+	case ALLOCATE_LEFT:
+		policy_name = "left";
+		break;
+	case ALLOCATE_RIGHT:
+		policy_name = "right";
+		break;
+	case ALLOCATE_NONE:
+		policy_name = "none";
+		break;
+	}
+
+	kunit_info(test, "%s: size=%zu, gfp=%x, policy=%s, cache=%i\n", __func__, size, gfp,
+		   policy_name, !!test_cache);
+
+	/*
+	 * 100x the sample interval should be more than enough to ensure we get
+	 * a KFENCE allocation eventually.
+	 */
+	timeout = jiffies + msecs_to_jiffies(100 * CONFIG_KFENCE_SAMPLE_INTERVAL);
+	/*
+	 * Especially for non-preemption kernels, ensure the allocation-gate
+	 * timer can catch up: after @resched_after, every failed allocation
+	 * attempt yields, to ensure the allocation-gate timer is scheduled.
+	 */
+	resched_after = jiffies + msecs_to_jiffies(CONFIG_KFENCE_SAMPLE_INTERVAL);
+	do {
+		if (test_cache)
+			alloc = kmem_cache_alloc(test_cache, gfp);
+		else
+			alloc = kmalloc(size, gfp);
+
+		if (is_kfence_address(alloc)) {
+			struct page *page = virt_to_head_page(alloc);
+			struct kmem_cache *s = test_cache ?: kmalloc_caches[kmalloc_type(GFP_KERNEL)][kmalloc_index(size)];
+
+			/*
+			 * Verify that various helpers return the right values
+			 * even for KFENCE objects; these are required so that
+			 * memcg accounting works correctly.
+			 */
+			KUNIT_EXPECT_EQ(test, obj_to_index(s, page, alloc), 0U);
+			KUNIT_EXPECT_EQ(test, objs_per_slab_page(s, page), 1);
+
+			if (policy == ALLOCATE_ANY)
+				return alloc;
+			if (policy == ALLOCATE_LEFT && IS_ALIGNED((unsigned long)alloc, PAGE_SIZE))
+				return alloc;
+			if (policy == ALLOCATE_RIGHT &&
+			    !IS_ALIGNED((unsigned long)alloc, PAGE_SIZE))
+				return alloc;
+		} else if (policy == ALLOCATE_NONE)
+			return alloc;
+
+		test_free(alloc);
+
+		if (time_after(jiffies, resched_after))
+			cond_resched();
+	} while (time_before(jiffies, timeout));
+
+	KUNIT_ASSERT_TRUE_MSG(test, false, "failed to allocate from KFENCE");
+	return NULL; /* Unreachable. */
+}
+
+static void test_out_of_bounds_read(struct kunit *test)
+{
+	size_t size = 32;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_OOB,
+		.fn = test_out_of_bounds_read,
+		.is_write = false,
+	};
+	char *buf;
+
+	setup_test_cache(test, size, 0, NULL);
+
+	/*
+	 * If we don't have our own cache, adjust based on alignment, so that we
+	 * actually access guard pages on either side.
+	 */
+	if (!test_cache)
+		size = kmalloc_cache_alignment(size);
+
+	/* Test both sides. */
+
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_LEFT);
+	expect.addr = buf - 1;
+	READ_ONCE(*expect.addr);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+	test_free(buf);
+
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_RIGHT);
+	expect.addr = buf + size;
+	READ_ONCE(*expect.addr);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+	test_free(buf);
+}
+
+static void test_out_of_bounds_write(struct kunit *test)
+{
+	size_t size = 32;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_OOB,
+		.fn = test_out_of_bounds_write,
+		.is_write = true,
+	};
+	char *buf;
+
+	setup_test_cache(test, size, 0, NULL);
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_LEFT);
+	expect.addr = buf - 1;
+	WRITE_ONCE(*expect.addr, 42);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+	test_free(buf);
+}
+
+static void test_use_after_free_read(struct kunit *test)
+{
+	const size_t size = 32;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_UAF,
+		.fn = test_use_after_free_read,
+		.is_write = false,
+	};
+
+	setup_test_cache(test, size, 0, NULL);
+	expect.addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+	test_free(expect.addr);
+	READ_ONCE(*expect.addr);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
+static void test_double_free(struct kunit *test)
+{
+	const size_t size = 32;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_INVALID_FREE,
+		.fn = test_double_free,
+	};
+
+	setup_test_cache(test, size, 0, NULL);
+	expect.addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+	test_free(expect.addr);
+	test_free(expect.addr); /* Double-free. */
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
+static void test_invalid_addr_free(struct kunit *test)
+{
+	const size_t size = 32;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_INVALID_FREE,
+		.fn = test_invalid_addr_free,
+	};
+	char *buf;
+
+	setup_test_cache(test, size, 0, NULL);
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+	expect.addr = buf + 1; /* Free on invalid address. */
+	test_free(expect.addr); /* Invalid address free. */
+	test_free(buf); /* No error. */
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
+static void test_corruption(struct kunit *test)
+{
+	size_t size = 32;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_CORRUPTION,
+		.fn = test_corruption,
+	};
+	char *buf;
+
+	setup_test_cache(test, size, 0, NULL);
+
+	/* Test both sides. */
+
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_LEFT);
+	expect.addr = buf + size;
+	WRITE_ONCE(*expect.addr, 42);
+	test_free(buf);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_RIGHT);
+	expect.addr = buf - 1;
+	WRITE_ONCE(*expect.addr, 42);
+	test_free(buf);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
+/*
+ * KFENCE is unable to detect an OOB if the allocation's alignment requirements
+ * leave a gap between the object and the guard page. Specifically, an
+ * allocation of e.g. 73 bytes is aligned on 8 and 128 bytes for SLUB or SLAB
+ * respectively. Therefore it is impossible for the allocated object to
+ * contiguously line up with the right guard page.
+ *
+ * However, we test that an access to memory beyond the gap results in KFENCE
+ * detecting an OOB access.
+ */
+static void test_kmalloc_aligned_oob_read(struct kunit *test)
+{
+	const size_t size = 73;
+	const size_t align = kmalloc_cache_alignment(size);
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_OOB,
+		.fn = test_kmalloc_aligned_oob_read,
+		.is_write = false,
+	};
+	char *buf;
+
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_RIGHT);
+
+	/*
+	 * The object is offset to the right, so there won't be an OOB to the
+	 * left of it.
+	 */
+	READ_ONCE(*(buf - 1));
+	KUNIT_EXPECT_FALSE(test, report_available());
+
+	/*
+	 * @buf must be aligned on @align, therefore buf + size belongs to the
+	 * same page -> no OOB.
+	 */
+	READ_ONCE(*(buf + size));
+	KUNIT_EXPECT_FALSE(test, report_available());
+
+	/* Overflowing by @align bytes will result in an OOB. */
+	expect.addr = buf + size + align;
+	READ_ONCE(*expect.addr);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+
+	test_free(buf);
+}
+
+static void test_kmalloc_aligned_oob_write(struct kunit *test)
+{
+	const size_t size = 73;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_CORRUPTION,
+		.fn = test_kmalloc_aligned_oob_write,
+	};
+	char *buf;
+
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_RIGHT);
+	/*
+	 * The object is offset to the right, so we won't get a page
+	 * fault immediately after it.
+	 */
+	expect.addr = buf + size;
+	WRITE_ONCE(*expect.addr, READ_ONCE(*expect.addr) + 1);
+	KUNIT_EXPECT_FALSE(test, report_available());
+	test_free(buf);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
+/* Test cache shrinking and destroying with KFENCE. */
+static void test_shrink_memcache(struct kunit *test)
+{
+	const size_t size = 32;
+	void *buf;
+
+	setup_test_cache(test, size, 0, NULL);
+	KUNIT_EXPECT_TRUE(test, test_cache);
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+	kmem_cache_shrink(test_cache);
+	test_free(buf);
+
+	KUNIT_EXPECT_FALSE(test, report_available());
+}
+
+static void ctor_set_x(void *obj)
+{
+	/* Every object has at least 8 bytes. */
+	memset(obj, 'x', 8);
+}
+
+/* Ensure that SL*B does not modify KFENCE objects on bulk free. */
+static void test_free_bulk(struct kunit *test)
+{
+	int iter;
+
+	for (iter = 0; iter < 5; iter++) {
+		const size_t size = setup_test_cache(test, 8 + prandom_u32_max(300), 0,
+						     (iter & 1) ? ctor_set_x : NULL);
+		void *objects[] = {
+			test_alloc(test, size, GFP_KERNEL, ALLOCATE_RIGHT),
+			test_alloc(test, size, GFP_KERNEL, ALLOCATE_NONE),
+			test_alloc(test, size, GFP_KERNEL, ALLOCATE_LEFT),
+			test_alloc(test, size, GFP_KERNEL, ALLOCATE_NONE),
+			test_alloc(test, size, GFP_KERNEL, ALLOCATE_NONE),
+		};
+
+		kmem_cache_free_bulk(test_cache, ARRAY_SIZE(objects), objects);
+		KUNIT_ASSERT_FALSE(test, report_available());
+		test_cache_destroy();
+	}
+}
+
+/* Test init-on-free works. */
+static void test_init_on_free(struct kunit *test)
+{
+	const size_t size = 32;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_UAF,
+		.fn = test_init_on_free,
+		.is_write = false,
+	};
+	int i;
+
+	if (!IS_ENABLED(CONFIG_INIT_ON_FREE_DEFAULT_ON))
+		return;
+	/* Assume it hasn't been disabled on command line. */
+
+	setup_test_cache(test, size, 0, NULL);
+	expect.addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+	for (i = 0; i < size; i++)
+		expect.addr[i] = i + 1;
+	test_free(expect.addr);
+
+	for (i = 0; i < size; i++) {
+		/*
+		 * This may fail if the page was recycled by KFENCE and then
+		 * written to again -- this however, is near impossible with a
+		 * default config.
+		 */
+		KUNIT_EXPECT_EQ(test, expect.addr[i], (char)0);
+
+		if (!i) /* Only check first access to not fail test if page is ever re-protected. */
+			KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+	}
+}
+
+/* Ensure that constructors work properly. */
+static void test_memcache_ctor(struct kunit *test)
+{
+	const size_t size = 32;
+	char *buf;
+	int i;
+
+	setup_test_cache(test, size, 0, ctor_set_x);
+	buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+
+	for (i = 0; i < 8; i++)
+		KUNIT_EXPECT_EQ(test, buf[i], (char)'x');
+
+	test_free(buf);
+
+	KUNIT_EXPECT_FALSE(test, report_available());
+}
+
+/* Test that memory is zeroed if requested. */
+static void test_gfpzero(struct kunit *test)
+{
+	const size_t size = PAGE_SIZE; /* PAGE_SIZE so we can use ALLOCATE_ANY. */
+	char *buf1, *buf2;
+	int i;
+
+	if (CONFIG_KFENCE_SAMPLE_INTERVAL > 100) {
+		kunit_warn(test, "skipping ... would take too long\n");
+		return;
+	}
+
+	setup_test_cache(test, size, 0, NULL);
+	buf1 = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+	for (i = 0; i < size; i++)
+		buf1[i] = i + 1;
+	test_free(buf1);
+
+	/* Try to get same address again -- this can take a while. */
+	for (i = 0;; i++) {
+		buf2 = test_alloc(test, size, GFP_KERNEL | __GFP_ZERO, ALLOCATE_ANY);
+		if (buf1 == buf2)
+			break;
+		test_free(buf2);
+
+		if (i == CONFIG_KFENCE_NUM_OBJECTS) {
+			kunit_warn(test, "giving up ... cannot get same object back\n");
+			return;
+		}
+	}
+
+	for (i = 0; i < size; i++)
+		KUNIT_EXPECT_EQ(test, buf2[i], (char)0);
+
+	test_free(buf2);
+
+	KUNIT_EXPECT_FALSE(test, report_available());
+}
+
+static void test_invalid_access(struct kunit *test)
+{
+	const struct expect_report expect = {
+		.type = KFENCE_ERROR_INVALID,
+		.fn = test_invalid_access,
+		.addr = &__kfence_pool[10],
+		.is_write = false,
+	};
+
+	READ_ONCE(__kfence_pool[10]);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
+/* Test SLAB_TYPESAFE_BY_RCU works. */
+static void test_memcache_typesafe_by_rcu(struct kunit *test)
+{
+	const size_t size = 32;
+	struct expect_report expect = {
+		.type = KFENCE_ERROR_UAF,
+		.fn = test_memcache_typesafe_by_rcu,
+		.is_write = false,
+	};
+
+	setup_test_cache(test, size, SLAB_TYPESAFE_BY_RCU, NULL);
+	KUNIT_EXPECT_TRUE(test, test_cache); /* Want memcache. */
+
+	expect.addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+	*expect.addr = 42;
+
+	rcu_read_lock();
+	test_free(expect.addr);
+	KUNIT_EXPECT_EQ(test, *expect.addr, (char)42);
+	/*
+	 * Up to this point, memory should not have been freed yet, and
+	 * therefore there should be no KFENCE report from the above access.
+	 */
+	rcu_read_unlock();
+
+	/* Above access to @expect.addr should not have generated a report! */
+	KUNIT_EXPECT_FALSE(test, report_available());
+
+	/* Only after rcu_barrier() is the memory guaranteed to be freed. */
+	rcu_barrier();
+
+	/* Expect use-after-free. */
+	KUNIT_EXPECT_EQ(test, *expect.addr, (char)42);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
+/* Test krealloc(). */
+static void test_krealloc(struct kunit *test)
+{
+	const size_t size = 32;
+	const struct expect_report expect = {
+		.type = KFENCE_ERROR_UAF,
+		.fn = test_krealloc,
+		.addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY),
+		.is_write = false,
+	};
+	char *buf = expect.addr;
+	int i;
+
+	KUNIT_EXPECT_FALSE(test, test_cache);
+	KUNIT_EXPECT_EQ(test, ksize(buf), size); /* Precise size match after KFENCE alloc. */
+	for (i = 0; i < size; i++)
+		buf[i] = i + 1;
+
+	/* Check that we successfully change the size. */
+	buf = krealloc(buf, size * 3, GFP_KERNEL); /* Grow. */
+	/* Note: Might no longer be a KFENCE alloc. */
+	KUNIT_EXPECT_GE(test, ksize(buf), size * 3);
+	for (i = 0; i < size; i++)
+		KUNIT_EXPECT_EQ(test, buf[i], (char)(i + 1));
+	for (; i < size * 3; i++) /* Fill to extra bytes. */
+		buf[i] = i + 1;
+
+	buf = krealloc(buf, size * 2, GFP_KERNEL); /* Shrink. */
+	KUNIT_EXPECT_GE(test, ksize(buf), size * 2);
+	for (i = 0; i < size * 2; i++)
+		KUNIT_EXPECT_EQ(test, buf[i], (char)(i + 1));
+
+	buf = krealloc(buf, 0, GFP_KERNEL); /* Free. */
+	KUNIT_EXPECT_EQ(test, (unsigned long)buf, (unsigned long)ZERO_SIZE_PTR);
+	KUNIT_ASSERT_FALSE(test, report_available()); /* No reports yet! */
+
+	READ_ONCE(*expect.addr); /* Ensure krealloc() actually freed earlier KFENCE object. */
+	KUNIT_ASSERT_TRUE(test, report_matches(&expect));
+}
+
+/* Test that some objects from a bulk allocation belong to KFENCE pool. */
+static void test_memcache_alloc_bulk(struct kunit *test)
+{
+	const size_t size = 32;
+	bool pass = false;
+	unsigned long timeout;
+
+	setup_test_cache(test, size, 0, NULL);
+	KUNIT_EXPECT_TRUE(test, test_cache); /* Want memcache. */
+	/*
+	 * 100x the sample interval should be more than enough to ensure we get
+	 * a KFENCE allocation eventually.
+	 */
+	timeout = jiffies + msecs_to_jiffies(100 * CONFIG_KFENCE_SAMPLE_INTERVAL);
+	do {
+		void *objects[100];
+		int i, num = kmem_cache_alloc_bulk(test_cache, GFP_ATOMIC, ARRAY_SIZE(objects),
+						   objects);
+		if (!num)
+			continue;
+		for (i = 0; i < ARRAY_SIZE(objects); i++) {
+			if (is_kfence_address(objects[i])) {
+				pass = true;
+				break;
+			}
+		}
+		kmem_cache_free_bulk(test_cache, num, objects);
+		/*
+		 * kmem_cache_alloc_bulk() disables interrupts, and calling it
+		 * in a tight loop may not give KFENCE a chance to switch the
+		 * static branch. Call cond_resched() to let KFENCE chime in.
+		 */
+		cond_resched();
+	} while (!pass && time_before(jiffies, timeout));
+
+	KUNIT_EXPECT_TRUE(test, pass);
+	KUNIT_EXPECT_FALSE(test, report_available());
+}
+
+/*
+ * KUnit does not provide a way to provide arguments to tests, and we encode
+ * additional info in the name. Set up 2 tests per test case, one using the
+ * default allocator, and another using a custom memcache (suffix '-memcache').
+ */
+#define KFENCE_KUNIT_CASE(test_name)						\
+	{ .run_case = test_name, .name = #test_name },				\
+	{ .run_case = test_name, .name = #test_name "-memcache" }
+
+static struct kunit_case kfence_test_cases[] = {
+	KFENCE_KUNIT_CASE(test_out_of_bounds_read),
+	KFENCE_KUNIT_CASE(test_out_of_bounds_write),
+	KFENCE_KUNIT_CASE(test_use_after_free_read),
+	KFENCE_KUNIT_CASE(test_double_free),
+	KFENCE_KUNIT_CASE(test_invalid_addr_free),
+	KFENCE_KUNIT_CASE(test_corruption),
+	KFENCE_KUNIT_CASE(test_free_bulk),
+	KFENCE_KUNIT_CASE(test_init_on_free),
+	KUNIT_CASE(test_kmalloc_aligned_oob_read),
+	KUNIT_CASE(test_kmalloc_aligned_oob_write),
+	KUNIT_CASE(test_shrink_memcache),
+	KUNIT_CASE(test_memcache_ctor),
+	KUNIT_CASE(test_invalid_access),
+	KUNIT_CASE(test_gfpzero),
+	KUNIT_CASE(test_memcache_typesafe_by_rcu),
+	KUNIT_CASE(test_krealloc),
+	KUNIT_CASE(test_memcache_alloc_bulk),
+	{},
+};
+
+/* ===== End test cases ===== */
+
+static int test_init(struct kunit *test)
+{
+	unsigned long flags;
+	int i;
+
+	spin_lock_irqsave(&observed.lock, flags);
+	for (i = 0; i < ARRAY_SIZE(observed.lines); i++)
+		observed.lines[i][0] = '\0';
+	observed.nlines = 0;
+	spin_unlock_irqrestore(&observed.lock, flags);
+
+	/* Any test with 'memcache' in its name will want a memcache. */
+	if (strstr(test->name, "memcache"))
+		test->priv = TEST_PRIV_WANT_MEMCACHE;
+	else
+		test->priv = NULL;
+
+	return 0;
+}
+
+static void test_exit(struct kunit *test)
+{
+	test_cache_destroy();
+}
+
+static struct kunit_suite kfence_test_suite = {
+	.name = "kfence",
+	.test_cases = kfence_test_cases,
+	.init = test_init,
+	.exit = test_exit,
+};
+static struct kunit_suite *kfence_test_suites[] = { &kfence_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().
+ */
+static int __init kfence_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(kfence_test_suites);
+}
+
+static void kfence_test_exit(void)
+{
+	__kunit_test_suites_exit(kfence_test_suites);
+	for_each_kernel_tracepoint(unregister_tracepoints, NULL);
+	tracepoint_synchronize_unregister();
+}
+
+late_initcall(kfence_test_init);
+module_exit(kfence_test_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Alexander Potapenko <[e-mail]>, Marco Elver <[e-mail]>");

mm/kfence/report.c

···
 	pr_cont(" ]");
 }
 
-void kfence_report_error(unsigned long address, struct pt_regs *regs,
+static const char *get_access_type(bool is_write)
+{
+	return is_write ? "write" : "read";
+}
+
+void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
 			 const struct kfence_metadata *meta, enum kfence_error_type type)
 {
 	unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 };
···
 	case KFENCE_ERROR_OOB: {
 		const bool left_of_object = address < meta->addr;
 
-		pr_err("BUG: KFENCE: out-of-bounds in %pS\n\n", (void *)stack_entries[skipnr]);
-		pr_err("Out-of-bounds access at 0x" PTR_FMT " (%luB %s of kfence-#%zd):\n",
-		       (void *)address,
+		pr_err("BUG: KFENCE: out-of-bounds %s in %pS\n\n", get_access_type(is_write),
+		       (void *)stack_entries[skipnr]);
+		pr_err("Out-of-bounds %s at 0x" PTR_FMT " (%luB %s of kfence-#%zd):\n",
+		       get_access_type(is_write), (void *)address,
 		       left_of_object ? meta->addr - address : address - meta->addr,
 		       left_of_object ? "left" : "right", object_index);
 		break;
 	}
 	case KFENCE_ERROR_UAF:
-		pr_err("BUG: KFENCE: use-after-free in %pS\n\n", (void *)stack_entries[skipnr]);
-		pr_err("Use-after-free access at 0x" PTR_FMT " (in kfence-#%zd):\n",
-		       (void *)address, object_index);
+		pr_err("BUG: KFENCE: use-after-free %s in %pS\n\n", get_access_type(is_write),
+		       (void *)stack_entries[skipnr]);
+		pr_err("Use-after-free %s at 0x" PTR_FMT " (in kfence-#%zd):\n",
+		       get_access_type(is_write), (void *)address, object_index);
 		break;
 	case KFENCE_ERROR_CORRUPTION:
 		pr_err("BUG: KFENCE: memory corruption in %pS\n\n", (void *)stack_entries[skipnr]);
···
 		pr_cont(" (in kfence-#%zd):\n", object_index);
 		break;
 	case KFENCE_ERROR_INVALID:
-		pr_err("BUG: KFENCE: invalid access in %pS\n\n", (void *)stack_entries[skipnr]);
-		pr_err("Invalid access at 0x" PTR_FMT ":\n", (void *)address);
+		pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write),
+		       (void *)stack_entries[skipnr]);
+		pr_err("Invalid %s at 0x" PTR_FMT ":\n", get_access_type(is_write),
+		       (void *)address);
 		break;
 	case KFENCE_ERROR_INVALID_FREE:
 		pr_err("BUG: KFENCE: invalid free in %pS\n\n", (void *)stack_entries[skipnr]);