hardening fixes for v6.15-rc3

- lib/prime_numbers: KUnit test should not select PRIME_NUMBERS
   (Geert Uytterhoeven)
 
 - ubsan: Fix panic from test_ubsan_out_of_bounds (Mostafa Saleh)
 
 - ubsan: Remove 'default UBSAN' from UBSAN_INTEGER_WRAP (Nathan Chancellor)
 
 - string: Add load_unaligned_zeropad() code path to sized_strscpy()
   (Peter Collingbourne)
 
 - kasan: Add strscpy() test to trigger tag fault on arm64 (Vincenzo
   Frascino)
 
 - Disable GCC randstruct for COMPILE_TEST
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Merge tag 'hardening-v6.15-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull hardening fixes from Kees Cook:

 - lib/prime_numbers: KUnit test should not select PRIME_NUMBERS (Geert
   Uytterhoeven)

 - ubsan: Fix panic from test_ubsan_out_of_bounds (Mostafa Saleh)

 - ubsan: Remove 'default UBSAN' from UBSAN_INTEGER_WRAP (Nathan
   Chancellor)

 - string: Add load_unaligned_zeropad() code path to sized_strscpy()
   (Peter Collingbourne)

 - kasan: Add strscpy() test to trigger tag fault on arm64 (Vincenzo
   Frascino)

 - Disable GCC randstruct for COMPILE_TEST

* tag 'hardening-v6.15-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  lib/prime_numbers: KUnit test should not select PRIME_NUMBERS
  ubsan: Fix panic from test_ubsan_out_of_bounds
  lib/Kconfig.ubsan: Remove 'default UBSAN' from UBSAN_INTEGER_WRAP
  hardening: Disable GCC randstruct for COMPILE_TEST
  kasan: Add strscpy() test to trigger tag fault on arm64
  string: Add load_unaligned_zeropad() code path to sized_strscpy()

lib/Kconfig.debug

@@ -3290,7 +3290,7 @@ config GCD_KUNIT_TEST
 config PRIME_NUMBERS_KUNIT_TEST
 	tristate "Prime number generator test" if !KUNIT_ALL_TESTS
 	depends on KUNIT
-	select PRIME_NUMBERS
+	depends on PRIME_NUMBERS
 	default KUNIT_ALL_TESTS
 	help
 	  This option enables the KUnit test suite for the {is,next}_prime_number

lib/Kconfig.ubsan

@@ -118,7 +118,6 @@ config UBSAN_UNREACHABLE
 
 config UBSAN_INTEGER_WRAP
 	bool "Perform checking for integer arithmetic wrap-around"
-	default UBSAN
 	depends on !COMPILE_TEST
 	depends on $(cc-option,-fsanitize-undefined-ignore-overflow-pattern=all)
 	depends on $(cc-option,-fsanitize=signed-integer-overflow)

lib/string.c

@@ -119,6 +119,7 @@ ssize_t sized_strscpy(char *dest, const char *src, size_t count)
 	if (count == 0 || WARN_ON_ONCE(count > INT_MAX))
 		return -E2BIG;
 
+#ifndef CONFIG_DCACHE_WORD_ACCESS
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 	/*
 	 * If src is unaligned, don't cross a page boundary,
@@ -133,12 +134,14 @@ ssize_t sized_strscpy(char *dest, const char *src, size_t count)
 	/* If src or dest is unaligned, don't do word-at-a-time. */
 	if (((long) dest | (long) src) & (sizeof(long) - 1))
 		max = 0;
+#endif
 #endif
 
 	/*
-	 * read_word_at_a_time() below may read uninitialized bytes after the
-	 * trailing zero and use them in comparisons. Disable this optimization
-	 * under KMSAN to prevent false positive reports.
+	 * load_unaligned_zeropad() or read_word_at_a_time() below may read
+	 * uninitialized bytes after the trailing zero and use them in
+	 * comparisons. Disable this optimization under KMSAN to prevent
+	 * false positive reports.
 	 */
 	if (IS_ENABLED(CONFIG_KMSAN))
 		max = 0;
@@ -146,7 +149,11 @@ ssize_t sized_strscpy(char *dest, const char *src, size_t count)
 	while (max >= sizeof(unsigned long)) {
 		unsigned long c, data;
 
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+		c = load_unaligned_zeropad(src+res);
+#else
 		c = read_word_at_a_time(src+res);
+#endif
 		if (has_zero(c, &data, &constants)) {
 			data = prep_zero_mask(c, data, &constants);
 			data = create_zero_mask(data);

lib/test_ubsan.c

@@ -77,18 +77,22 @@ static void test_ubsan_shift_out_of_bounds(void)
 
 static void test_ubsan_out_of_bounds(void)
 {
-	volatile int i = 4, j = 5, k = -1;
-	volatile char above[4] = { }; /* Protect surrounding memory. */
-	volatile int arr[4];
-	volatile char below[4] = { }; /* Protect surrounding memory. */
+	int i = 4, j = 4, k = -1;
+	volatile struct {
+		char above[4]; /* Protect surrounding memory. */
+		int arr[4];
+		char below[4]; /* Protect surrounding memory. */
+	} data;
 
-	above[0] = below[0];
+	OPTIMIZER_HIDE_VAR(i);
+	OPTIMIZER_HIDE_VAR(j);
+	OPTIMIZER_HIDE_VAR(k);
 
 	UBSAN_TEST(CONFIG_UBSAN_BOUNDS, "above");
-	arr[j] = i;
+	data.arr[j] = i;
 
 	UBSAN_TEST(CONFIG_UBSAN_BOUNDS, "below");
-	arr[k] = i;
+	data.arr[k] = i;
 }
 
 enum ubsan_test_enum {

mm/kasan/kasan_test_c.c

@@ -1567,6 +1567,7 @@ static void kasan_memcmp(struct kunit *test)
 static void kasan_strings(struct kunit *test)
 {
 	char *ptr;
+	char *src;
 	size_t size = 24;
 
 	/*
@@ -1578,6 +1579,25 @@ static void kasan_strings(struct kunit *test)
 	ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	src = kmalloc(KASAN_GRANULE_SIZE, GFP_KERNEL | __GFP_ZERO);
+	strscpy(src, "f0cacc1a0000000", KASAN_GRANULE_SIZE);
+
+	/*
+	 * Make sure that strscpy() does not trigger KASAN if it overreads into
+	 * poisoned memory.
+	 *
+	 * The expected size does not include the terminator '\0'
+	 * so it is (KASAN_GRANULE_SIZE - 2) ==
+	 * KASAN_GRANULE_SIZE - ("initial removed character" + "\0").
+	 */
+	KUNIT_EXPECT_EQ(test, KASAN_GRANULE_SIZE - 2,
+			strscpy(ptr, src + 1, KASAN_GRANULE_SIZE));
+
+	/* strscpy should fail if the first byte is unreadable. */
+	KUNIT_EXPECT_KASAN_FAIL(test, strscpy(ptr, src + KASAN_GRANULE_SIZE,
+					      KASAN_GRANULE_SIZE));
+
+	kfree(src);
 	kfree(ptr);
 
 	/*

security/Kconfig.hardening

@@ -344,7 +344,7 @@ config CC_HAS_RANDSTRUCT
 
 choice
 	prompt "Randomize layout of sensitive kernel structures"
-	default RANDSTRUCT_FULL if COMPILE_TEST && (GCC_PLUGINS || CC_HAS_RANDSTRUCT)
+	default RANDSTRUCT_FULL if COMPILE_TEST && CC_HAS_RANDSTRUCT
 	default RANDSTRUCT_NONE
 	help
 	  If you enable this, the layouts of structures that are entirely

tools/testing/selftests/lib/config

@@ -1,2 +1,3 @@
 CONFIG_TEST_BITMAP=m
+CONFIG_PRIME_NUMBERS=m
 CONFIG_TEST_BITOPS=m