[PATCH v3 0/5] fortify: Add KUnit tests for runtime overflows

[PATCH v3 0/5] fortify: Add KUnit tests for runtime overflows

[Kees Cook]

Hi,

This series is the rest of the v2 series that was half landed last year,
and finally introduces KUnit runtime testing of the CONFIG_FORTIFY_SOURCE
APIs. Additionally FORTIFY failure messages are improved to give more
context about read/write and sizes.

-Kees

v3
 - rebase (goodbye strlcpy)
 - avoid extra macros for replacing fortify_panic() (nick)
 - generally clean up macro usage
 - avoid build warnings when testing known overflow conditions
v2 https://lore.kernel.org/all/20230407192717.636137-10-keescook@chromium.org/
v1 https://lore.kernel.org/lkml/20230405235832.never.487-kees@kernel.org/

Kees Cook (5):
  fortify: Split reporting and avoid passing string pointer
  fortify: Allow KUnit test to build without FORTIFY
  fortify: Provide KUnit counters for failure testing
  fortify: Add KUnit tests for runtime overflows
  fortify: Improve buffer overflow reporting

 arch/arm/boot/compressed/misc.c |   2 +-
 arch/x86/boot/compressed/misc.c |   2 +-
 include/linux/fortify-string.h  | 100 +++--
 lib/Kconfig.debug               |   2 +-
 lib/Makefile                    |   1 +
 lib/fortify_kunit.c             | 662 +++++++++++++++++++++++++++++++-
 lib/string_helpers.c            |  26 +-
 tools/objtool/noreturns.h       |   2 +-
 8 files changed, 761 insertions(+), 36 deletions(-)

-- 
2.34.1

[PATCH v3 1/5] fortify: Split reporting and avoid passing string pointer

[Kees Cook]

In preparation for KUnit testing and further improvements in fortify
failure reporting, split out the report and encode the function and access
failure (read or write overflow) into a single u8 argument. This mainly
ends up saving a tiny bit of space in the data segment. For a defconfig
with FORTIFY_SOURCE enabled:

$ size gcc/vmlinux.before gcc/vmlinux.after
   text  	  data     bss     dec    	    hex filename
26132309        9760658 2195460 38088427        2452eeb gcc/vmlinux.before
26132386        9748382 2195460 38076228        244ff44 gcc/vmlinux.after

Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
Cc: linux-hardening@vger.kernel.org
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Cezary Rojewski <cezary.rojewski@intel.com>
Cc: Puyou Lu <puyou.lu@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
---
 arch/arm/boot/compressed/misc.c |  2 +-
 arch/x86/boot/compressed/misc.c |  2 +-
 include/linux/fortify-string.h  | 81 ++++++++++++++++++++++++---------
 lib/string_helpers.c            | 23 ++++++++--
 tools/objtool/noreturns.h       |  2 +-
 5 files changed, 83 insertions(+), 27 deletions(-)

diff --git a/arch/arm/boot/compressed/misc.c b/arch/arm/boot/compressed/misc.c
index 6b4baa6a9a50..d93e2e466f6a 100644
--- a/arch/arm/boot/compressed/misc.c
+++ b/arch/arm/boot/compressed/misc.c
@@ -154,7 +154,7 @@ decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p,
 		putstr(" done, booting the kernel.\n");
 }
 
-void fortify_panic(const char *name)
+void __fortify_panic(const u8 reason)
 {
 	error("detected buffer overflow");
 }
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index b99e08e6815b..c9971b9dbb09 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -496,7 +496,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
 	return output + entry_offset;
 }
 
-void fortify_panic(const char *name)
+void __fortify_panic(const u8 reason)
 {
 	error("detected buffer overflow");
 }
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 06b3aaa63724..4f6767dcd933 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_FORTIFY_STRING_H_
 #define _LINUX_FORTIFY_STRING_H_
 
+#include <linux/bitfield.h>
 #include <linux/bug.h>
 #include <linux/const.h>
 #include <linux/limits.h>
@@ -9,7 +10,44 @@
 #define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable
 #define __RENAME(x) __asm__(#x)
 
-void fortify_panic(const char *name) __noreturn __cold;
+#define FORTIFY_REASON_DIR(r)		FIELD_GET(BIT(0), r)
+#define FORTIFY_REASON_FUNC(r)		FIELD_GET(GENMASK(7, 1), r)
+#define FORTIFY_REASON(func, write)	(FIELD_PREP(BIT(0), write) | \
+					 FIELD_PREP(GENMASK(7, 1), func))
+
+#define fortify_panic(func, write)	\
+	__fortify_panic(FORTIFY_REASON(func, write))
+
+#define FORTIFY_READ		 0
+#define FORTIFY_WRITE		 1
+
+#define EACH_FORTIFY_FUNC(macro)	\
+	macro(strncpy),			\
+	macro(strnlen),			\
+	macro(strlen),			\
+	macro(strscpy),			\
+	macro(strlcat),			\
+	macro(strcat),			\
+	macro(strncat),			\
+	macro(memset),			\
+	macro(memcpy),			\
+	macro(memmove),			\
+	macro(memscan),			\
+	macro(memcmp),			\
+	macro(memchr),			\
+	macro(memchr_inv),		\
+	macro(kmemdup),			\
+	macro(strcpy),			\
+	macro(UNKNOWN),
+
+#define MAKE_FORTIFY_FUNC(func)	FORTIFY_FUNC_##func
+
+enum fortify_func {
+	EACH_FORTIFY_FUNC(MAKE_FORTIFY_FUNC)
+};
+
+void __fortify_report(const u8 reason);
+void __fortify_panic(const u8 reason) __cold __noreturn;
 void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)");
 void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");
 void __read_overflow2_field(size_t avail, size_t wanted) __compiletime_warning("detected read beyond size of field (2nd parameter); maybe use struct_group()?");
@@ -143,7 +181,7 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__write_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE);
 	return __underlying_strncpy(p, q, size);
 }
 
@@ -174,7 +212,7 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size
 	/* Do not check characters beyond the end of p. */
 	ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
 	if (p_size <= ret && maxlen != ret)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ);
 	return ret;
 }
 
@@ -210,7 +248,7 @@ __kernel_size_t __fortify_strlen(const char * const POS p)
 		return __underlying_strlen(p);
 	ret = strnlen(p, p_size);
 	if (p_size <= ret)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ);
 	return ret;
 }
 
@@ -261,7 +299,7 @@ __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const PO
 	 * p_size.
 	 */
 	if (len > p_size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE);
 
 	/*
 	 * We can now safely call vanilla strscpy because we are protected from:
@@ -319,7 +357,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail)
 
 	/* Give up if string is already overflowed. */
 	if (p_size <= p_len)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ);
 
 	if (actual >= avail) {
 		copy_len = avail - p_len - 1;
@@ -328,7 +366,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail)
 
 	/* Give up if copy will overflow. */
 	if (p_size <= actual)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE);
 	__underlying_memcpy(p + p_len, q, copy_len);
 	p[actual] = '\0';
 
@@ -357,7 +395,7 @@ char *strcat(char * const POS p, const char *q)
 	const size_t p_size = __member_size(p);
 
 	if (strlcat(p, q, p_size) >= p_size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE);
 	return p;
 }
 
@@ -393,7 +431,7 @@ char *strncat(char * const POS p, const char * const POS q, __kernel_size_t coun
 	p_len = strlen(p);
 	copy_len = strnlen(q, count);
 	if (p_size < p_len + copy_len + 1)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE);
 	__underlying_memcpy(p + p_len, q, copy_len);
 	p[p_len + copy_len] = '\0';
 	return p;
@@ -434,7 +472,7 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
 	 * lengths are unknown.)
 	 */
 	if (p_size != SIZE_MAX && p_size < size)
-		fortify_panic("memset");
+		fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE);
 }
 
 #define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({	\
@@ -488,7 +526,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
 					 const size_t q_size,
 					 const size_t p_size_field,
 					 const size_t q_size_field,
-					 const char *func)
+					 const u8 func)
 {
 	if (__builtin_constant_p(size)) {
 		/*
@@ -532,9 +570,10 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
 	 * (The SIZE_MAX test is to optimize away checks where the buffer
 	 * lengths are unknown.)
 	 */
-	if ((p_size != SIZE_MAX && p_size < size) ||
-	    (q_size != SIZE_MAX && q_size < size))
-		fortify_panic(func);
+	if (p_size != SIZE_MAX && p_size < size)
+		fortify_panic(func, FORTIFY_WRITE);
+	else if (q_size != SIZE_MAX && q_size < size)
+		fortify_panic(func, FORTIFY_READ);
 
 	/*
 	 * Warn when writing beyond destination field size.
@@ -567,7 +606,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
 	const size_t __q_size_field = (q_size_field);			\
 	WARN_ONCE(fortify_memcpy_chk(__fortify_size, __p_size,		\
 				     __q_size, __p_size_field,		\
-				     __q_size_field, #op),		\
+				     __q_size_field, FORTIFY_FUNC_ ##op), \
 		  #op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \
 		  __fortify_size,					\
 		  "field \"" #p "\" at " FILE_LINE,			\
@@ -634,7 +673,7 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ);
 	return __real_memscan(p, c, size);
 }
 
@@ -651,7 +690,7 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t
 			__read_overflow2();
 	}
 	if (p_size < size || q_size < size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ);
 	return __underlying_memcmp(p, q, size);
 }
 
@@ -663,7 +702,7 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ);
 	return __underlying_memchr(p, c, size);
 }
 
@@ -675,7 +714,7 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ);
 	return __real_memchr_inv(p, c, size);
 }
 
@@ -688,7 +727,7 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ);
 	return __real_kmemdup(p, size, gfp);
 }
 
@@ -725,7 +764,7 @@ char *strcpy(char * const POS p, const char * const POS q)
 		__write_overflow();
 	/* Run-time check for dynamic size overflow. */
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE);
 	__underlying_memcpy(p, q, size);
 	return p;
 }
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 606c3099013f..9291dc74ae01 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -1008,10 +1008,27 @@ EXPORT_SYMBOL(__read_overflow2_field);
 void __write_overflow_field(size_t avail, size_t wanted) { }
 EXPORT_SYMBOL(__write_overflow_field);
 
-void fortify_panic(const char *name)
+static const char * const fortify_func_name[] = {
+#define MAKE_FORTIFY_FUNC_NAME(func)	[MAKE_FORTIFY_FUNC(func)] = #func
+	EACH_FORTIFY_FUNC(MAKE_FORTIFY_FUNC_NAME)
+#undef  MAKE_FORTIFY_FUNC_NAME
+};
+
+void __fortify_report(const u8 reason)
+{
+	const u8 func = FORTIFY_REASON_FUNC(reason);
+	const bool write = FORTIFY_REASON_DIR(reason);
+	const char *name;
+
+	name = fortify_func_name[umin(func, FORTIFY_FUNC_UNKNOWN)];
+	WARN(1, "%s: detected buffer %s overflow\n", name, str_read_write(!write));
+}
+EXPORT_SYMBOL(__fortify_report);
+
+void __fortify_panic(const u8 reason)
 {
-	pr_emerg("detected buffer overflow in %s\n", name);
+	__fortify_report(reason);
 	BUG();
 }
-EXPORT_SYMBOL(fortify_panic);
+EXPORT_SYMBOL(__fortify_panic);
 #endif /* CONFIG_FORTIFY_SOURCE */
diff --git a/tools/objtool/noreturns.h b/tools/objtool/noreturns.h
index 1685d7ea6a9f..3a301696f005 100644
--- a/tools/objtool/noreturns.h
+++ b/tools/objtool/noreturns.h
@@ -6,6 +6,7 @@
  *
  * Yes, this is unfortunate.  A better solution is in the works.
  */
+NORETURN(__fortify_panic)
 NORETURN(__kunit_abort)
 NORETURN(__module_put_and_kthread_exit)
 NORETURN(__reiserfs_panic)
@@ -22,7 +23,6 @@ NORETURN(do_exit)
 NORETURN(do_group_exit)
 NORETURN(do_task_dead)
 NORETURN(ex_handler_msr_mce)
-NORETURN(fortify_panic)
 NORETURN(hlt_play_dead)
 NORETURN(hv_ghcb_terminate)
 NORETURN(kthread_complete_and_exit)
-- 
2.34.1

[PATCH v3 2/5] fortify: Allow KUnit test to build without FORTIFY

[Kees Cook]

In order for CI systems to notice all the skipped tests related to
CONFIG_FORTIFY_SOURCE, allow the FORTIFY_SOURCE KUnit tests to build
with or without CONFIG_FORTIFY_SOURCE.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
Cc: linux-hardening@vger.kernel.org
---
 lib/Kconfig.debug   |  2 +-
 lib/fortify_kunit.c | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 975a07f9f1cc..4e2febe3b568 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2748,7 +2748,7 @@ config STACKINIT_KUNIT_TEST
 
 config FORTIFY_KUNIT_TEST
 	tristate "Test fortified str*() and mem*() function internals at runtime" if !KUNIT_ALL_TESTS
-	depends on KUNIT && FORTIFY_SOURCE
+	depends on KUNIT
 	default KUNIT_ALL_TESTS
 	help
 	  Builds unit tests for checking internals of FORTIFY_SOURCE as used
diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
index 2e4fedc81621..7a88b5dd3d27 100644
--- a/lib/fortify_kunit.c
+++ b/lib/fortify_kunit.c
@@ -22,6 +22,11 @@
 #include <linux/string.h>
 #include <linux/vmalloc.h>
 
+/* Handle being built without CONFIG_FORTIFY_SOURCE */
+#ifndef __compiletime_strlen
+# define __compiletime_strlen __builtin_strlen
+#endif
+
 static const char array_of_10[] = "this is 10";
 static const char *ptr_of_11 = "this is 11!";
 static char array_unknown[] = "compiler thinks I might change";
@@ -308,6 +313,14 @@ DEFINE_ALLOC_SIZE_TEST_PAIR(kvmalloc)
 } while (0)
 DEFINE_ALLOC_SIZE_TEST_PAIR(devm_kmalloc)
 
+static int fortify_test_init(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_FORTIFY_SOURCE))
+		kunit_skip(test, "Not built with CONFIG_FORTIFY_SOURCE=y");
+
+	return 0;
+}
+
 static struct kunit_case fortify_test_cases[] = {
 	KUNIT_CASE(known_sizes_test),
 	KUNIT_CASE(control_flow_split_test),
@@ -324,6 +337,7 @@ static struct kunit_case fortify_test_cases[] = {
 
 static struct kunit_suite fortify_test_suite = {
 	.name = "fortify",
+	.init = fortify_test_init,
 	.test_cases = fortify_test_cases,
 };
 
-- 
2.34.1

[PATCH v3 3/5] fortify: Provide KUnit counters for failure testing

[Kees Cook]

The standard C string APIs were not designed to have a failure mode;
they were expected to always succeed without memory safety issues.
Normally, CONFIG_FORTIFY_SOURCE will use fortify_panic() to stop
processing, as truncating a read or write may provide an even worse
system state. However, this creates a problem for testing under things
like KUnit, which needs a way to survive failures.

When building with CONFIG_KUNIT, provide a failure path for all users
of fortify_panic, and track whether the failure was a read overflow or
a write overflow, for KUnit tests to examine. Inspired by similar logic
in the slab tests.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
Cc: linux-hardening@vger.kernel.org
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: David Gow <davidgow@google.com>
Cc: kunit-dev@googlegroups.com
---
 include/linux/fortify-string.h | 43 ++++++++++++++++++----------------
 lib/fortify_kunit.c            | 41 ++++++++++++++++++++++++++++++++
 lib/string_helpers.c           |  2 ++
 3 files changed, 66 insertions(+), 20 deletions(-)

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 4f6767dcd933..fbfb90479b8f 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -15,8 +15,10 @@
 #define FORTIFY_REASON(func, write)	(FIELD_PREP(BIT(0), write) | \
 					 FIELD_PREP(GENMASK(7, 1), func))
 
-#define fortify_panic(func, write)	\
-	__fortify_panic(FORTIFY_REASON(func, write))
+#ifndef fortify_panic
+# define fortify_panic(func, write, retfail)	\
+	 __fortify_panic(FORTIFY_REASON(func, write))
+#endif
 
 #define FORTIFY_READ		 0
 #define FORTIFY_WRITE		 1
@@ -181,7 +183,7 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__write_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE);
+		fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE, p);
 	return __underlying_strncpy(p, q, size);
 }
 
@@ -212,7 +214,7 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size
 	/* Do not check characters beyond the end of p. */
 	ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
 	if (p_size <= ret && maxlen != ret)
-		fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ);
+		fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ, ret);
 	return ret;
 }
 
@@ -248,7 +250,7 @@ __kernel_size_t __fortify_strlen(const char * const POS p)
 		return __underlying_strlen(p);
 	ret = strnlen(p, p_size);
 	if (p_size <= ret)
-		fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ);
+		fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ, ret);
 	return ret;
 }
 
@@ -299,7 +301,7 @@ __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const PO
 	 * p_size.
 	 */
 	if (len > p_size)
-		fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE);
+		fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE, -E2BIG);
 
 	/*
 	 * We can now safely call vanilla strscpy because we are protected from:
@@ -357,7 +359,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail)
 
 	/* Give up if string is already overflowed. */
 	if (p_size <= p_len)
-		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ);
+		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ, wanted);
 
 	if (actual >= avail) {
 		copy_len = avail - p_len - 1;
@@ -366,7 +368,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail)
 
 	/* Give up if copy will overflow. */
 	if (p_size <= actual)
-		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE);
+		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE, wanted);
 	__underlying_memcpy(p + p_len, q, copy_len);
 	p[actual] = '\0';
 
@@ -395,7 +397,7 @@ char *strcat(char * const POS p, const char *q)
 	const size_t p_size = __member_size(p);
 
 	if (strlcat(p, q, p_size) >= p_size)
-		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE);
+		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p);
 	return p;
 }
 
@@ -431,13 +433,13 @@ char *strncat(char * const POS p, const char * const POS q, __kernel_size_t coun
 	p_len = strlen(p);
 	copy_len = strnlen(q, count);
 	if (p_size < p_len + copy_len + 1)
-		fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE);
+		fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE, p);
 	__underlying_memcpy(p + p_len, q, copy_len);
 	p[p_len + copy_len] = '\0';
 	return p;
 }
 
-__FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
+__FORTIFY_INLINE bool fortify_memset_chk(__kernel_size_t size,
 					 const size_t p_size,
 					 const size_t p_size_field)
 {
@@ -472,7 +474,8 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
 	 * lengths are unknown.)
 	 */
 	if (p_size != SIZE_MAX && p_size < size)
-		fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE);
+		fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE, true);
+	return false;
 }
 
 #define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({	\
@@ -571,9 +574,9 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
 	 * lengths are unknown.)
 	 */
 	if (p_size != SIZE_MAX && p_size < size)
-		fortify_panic(func, FORTIFY_WRITE);
+		fortify_panic(func, FORTIFY_WRITE, true);
 	else if (q_size != SIZE_MAX && q_size < size)
-		fortify_panic(func, FORTIFY_READ);
+		fortify_panic(func, FORTIFY_READ, true);
 
 	/*
 	 * Warn when writing beyond destination field size.
@@ -673,7 +676,7 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ);
+		fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ, NULL);
 	return __real_memscan(p, c, size);
 }
 
@@ -690,7 +693,7 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t
 			__read_overflow2();
 	}
 	if (p_size < size || q_size < size)
-		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ);
+		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, INT_MIN);
 	return __underlying_memcmp(p, q, size);
 }
 
@@ -702,7 +705,7 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ);
+		fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ, NULL);
 	return __underlying_memchr(p, c, size);
 }
 
@@ -714,7 +717,7 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ);
+		fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ, NULL);
 	return __real_memchr_inv(p, c, size);
 }
 
@@ -727,7 +730,7 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ);
+		fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ, NULL);
 	return __real_kmemdup(p, size, gfp);
 }
 
@@ -764,7 +767,7 @@ char *strcpy(char * const POS p, const char * const POS q)
 		__write_overflow();
 	/* Run-time check for dynamic size overflow. */
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE);
+		fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE, p);
 	__underlying_memcpy(p, q, size);
 	return p;
 }
diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
index 7a88b5dd3d27..4ba7d02fdd78 100644
--- a/lib/fortify_kunit.c
+++ b/lib/fortify_kunit.c
@@ -15,8 +15,17 @@
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+/* Redefine fortify_panic() to track failures. */
+void fortify_add_kunit_error(int write);
+#define fortify_panic(func, write, retfail) do {			\
+	__fortify_report(FORTIFY_REASON(func, write));			\
+	fortify_add_kunit_error(write);					\
+	return (retfail);						\
+} while (0)
+
 #include <kunit/device.h>
 #include <kunit/test.h>
+#include <kunit/test-bug.h>
 #include <linux/device.h>
 #include <linux/slab.h>
 #include <linux/string.h>
@@ -27,10 +36,34 @@
 # define __compiletime_strlen __builtin_strlen
 #endif
 
+static struct kunit_resource read_resource;
+static struct kunit_resource write_resource;
+static int fortify_read_overflows;
+static int fortify_write_overflows;
+
 static const char array_of_10[] = "this is 10";
 static const char *ptr_of_11 = "this is 11!";
 static char array_unknown[] = "compiler thinks I might change";
 
+void fortify_add_kunit_error(int write)
+{
+	struct kunit_resource *resource;
+	struct kunit *current_test;
+
+	current_test = kunit_get_current_test();
+	if (!current_test)
+		return;
+
+	resource = kunit_find_named_resource(current_test,
+			write ? "fortify_write_overflows"
+			      : "fortify_read_overflows");
+	if (!resource)
+		return;
+
+	(*(int *)resource->data)++;
+	kunit_put_resource(resource);
+}
+
 static void known_sizes_test(struct kunit *test)
 {
 	KUNIT_EXPECT_EQ(test, __compiletime_strlen("88888888"), 8);
@@ -318,6 +351,14 @@ static int fortify_test_init(struct kunit *test)
 	if (!IS_ENABLED(CONFIG_FORTIFY_SOURCE))
 		kunit_skip(test, "Not built with CONFIG_FORTIFY_SOURCE=y");
 
+	fortify_read_overflows = 0;
+	kunit_add_named_resource(test, NULL, NULL, &read_resource,
+				 "fortify_read_overflows",
+				 &fortify_read_overflows);
+	fortify_write_overflows = 0;
+	kunit_add_named_resource(test, NULL, NULL, &write_resource,
+				 "fortify_write_overflows",
+				 &fortify_write_overflows);
 	return 0;
 }
 
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 9291dc74ae01..5e53d42e32bb 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -18,6 +18,8 @@
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/string_helpers.h>
+#include <kunit/test.h>
+#include <kunit/test-bug.h>
 
 /**
  * string_get_size - get the size in the specified units
-- 
2.34.1

[PATCH v3 4/5] fortify: Add KUnit tests for runtime overflows

[Kees Cook]

With fortify overflows able to be redirected, we can use KUnit to
exercise the overflow conditions. Add tests for every API covered by
CONFIG_FORTIFY_SOURCE, except for memset() and memcpy(), which are
special-cased for now.

Note that this makes the LKDTM FORTIFY_STR* tests obsolete, but those
can be removed separately.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
Cc: linux-hardening@vger.kernel.org
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: kunit-dev@googlegroups.com
---
 lib/Makefile        |   1 +
 lib/fortify_kunit.c | 607 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 606 insertions(+), 2 deletions(-)

diff --git a/lib/Makefile b/lib/Makefile
index bc36a5c167db..9d0e2af8100a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -402,6 +402,7 @@ obj-$(CONFIG_OVERFLOW_KUNIT_TEST) += overflow_kunit.o
 CFLAGS_stackinit_kunit.o += $(call cc-disable-warning, switch-unreachable)
 obj-$(CONFIG_STACKINIT_KUNIT_TEST) += stackinit_kunit.o
 CFLAGS_fortify_kunit.o += $(call cc-disable-warning, unsequenced)
+CFLAGS_fortify_kunit.o += $(call cc-disable-warning, stringop-overread)
 CFLAGS_fortify_kunit.o += $(DISABLE_STRUCTLEAK_PLUGIN)
 obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_kunit.o
 obj-$(CONFIG_STRCAT_KUNIT_TEST) += strcat_kunit.o
diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
index 4ba7d02fdd78..f0accebeca02 100644
--- a/lib/fortify_kunit.c
+++ b/lib/fortify_kunit.c
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * Runtime test cases for CONFIG_FORTIFY_SOURCE that aren't expected to
- * Oops the kernel on success. (For those, see drivers/misc/lkdtm/fortify.c)
+ * Runtime test cases for CONFIG_FORTIFY_SOURCE. For testing memcpy(),
+ * see FORTIFY_MEM_* tests in LKDTM (drivers/misc/lkdtm/fortify.c).
  *
  * For corner cases with UBSAN, try testing with:
  *
@@ -346,6 +346,594 @@ DEFINE_ALLOC_SIZE_TEST_PAIR(kvmalloc)
 } while (0)
 DEFINE_ALLOC_SIZE_TEST_PAIR(devm_kmalloc)
 
+/*
+ * We can't have an array at the end of a structure or else
+ * builds without -fstrict-flex-arrays=3 will report them as
+ * being an unknown length. Additionally, add bytes before
+ * and after the string to catch over/underflows if tests
+ * fail.
+ */
+struct fortify_padding {
+	unsigned long bytes_before;
+	char buf[32];
+	unsigned long bytes_after;
+};
+/* Force compiler into not being able to resolve size at compile-time. */
+static volatile int unconst;
+
+static void strlen_test(struct kunit *test)
+{
+	struct fortify_padding pad = { };
+	int i, end = sizeof(pad.buf) - 1;
+
+	/* Fill 31 bytes with valid characters. */
+	for (i = 0; i < sizeof(pad.buf) - 1; i++)
+		pad.buf[i] = i + '0';
+	/* Trailing bytes are still %NUL. */
+	KUNIT_EXPECT_EQ(test, pad.buf[end], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* String is terminated, so strlen() is valid. */
+	KUNIT_EXPECT_EQ(test, strlen(pad.buf), end);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+
+	/* Make string unterminated, and recount. */
+	pad.buf[end] = 'A';
+	end = sizeof(pad.buf);
+	KUNIT_EXPECT_EQ(test, strlen(pad.buf), end);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+}
+
+static void strnlen_test(struct kunit *test)
+{
+	struct fortify_padding pad = { };
+	int i, end = sizeof(pad.buf) - 1;
+
+	/* Fill 31 bytes with valid characters. */
+	for (i = 0; i < sizeof(pad.buf) - 1; i++)
+		pad.buf[i] = i + '0';
+	/* Trailing bytes are still %NUL. */
+	KUNIT_EXPECT_EQ(test, pad.buf[end], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* String is terminated, so strnlen() is valid. */
+	KUNIT_EXPECT_EQ(test, strnlen(pad.buf, sizeof(pad.buf)), end);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	/* A truncated strnlen() will be safe, too. */
+	KUNIT_EXPECT_EQ(test, strnlen(pad.buf, sizeof(pad.buf) / 2),
+					sizeof(pad.buf) / 2);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+
+	/* Make string unterminated, and recount. */
+	pad.buf[end] = 'A';
+	end = sizeof(pad.buf);
+	/* Reading beyond with strncpy() will fail. */
+	KUNIT_EXPECT_EQ(test, strnlen(pad.buf, end + 1), end);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+	KUNIT_EXPECT_EQ(test, strnlen(pad.buf, end + 2), end);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+
+	/* Early-truncated is safe still, though. */
+	KUNIT_EXPECT_EQ(test, strnlen(pad.buf, end), end);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+
+	end = sizeof(pad.buf) / 2;
+	KUNIT_EXPECT_EQ(test, strnlen(pad.buf, end), end);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+}
+
+static void strcpy_test(struct kunit *test)
+{
+	struct fortify_padding pad = { };
+	char src[sizeof(pad.buf) + 1] = { };
+	int i;
+
+	/* Fill 31 bytes with valid characters. */
+	for (i = 0; i < sizeof(src) - 2; i++)
+		src[i] = i + '0';
+
+	/* Destination is %NUL-filled to start with. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_before, 0);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Legitimate strcpy() 1 less than of max size. */
+	KUNIT_ASSERT_TRUE(test, strcpy(pad.buf, src)
+				== pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Only last byte should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	src[sizeof(src) - 2] = 'A';
+	/* But now we trip the overflow checking. */
+	KUNIT_ASSERT_TRUE(test, strcpy(pad.buf, src)
+				== pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1);
+	/* Trailing %NUL -- thanks to FORTIFY. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	/* And we will not have gone beyond. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	src[sizeof(src) - 1] = 'A';
+	/* And for sure now, two bytes past. */
+	KUNIT_ASSERT_TRUE(test, strcpy(pad.buf, src)
+				== pad.buf);
+	/*
+	 * Which trips both the strlen() on the unterminated src,
+	 * and the resulting copy attempt.
+	 */
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
+	/* Trailing %NUL -- thanks to FORTIFY. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	/* And we will not have gone beyond. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+}
+
+static void strncpy_test(struct kunit *test)
+{
+	struct fortify_padding pad = { };
+	char src[] = "Copy me fully into a small buffer and I will overflow!";
+
+	/* Destination is %NUL-filled to start with. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_before, 0);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Legitimate strncpy() 1 less than of max size. */
+	KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src,
+					sizeof(pad.buf) + unconst - 1)
+				== pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Only last byte should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	/* Legitimate (though unterminated) max-size strncpy. */
+	KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src,
+					sizeof(pad.buf) + unconst)
+				== pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* No trailing %NUL -- thanks strncpy API. */
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	/* But we will not have gone beyond. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Now verify that FORTIFY is working... */
+	KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src,
+					sizeof(pad.buf) + unconst + 1)
+				== pad.buf);
+	/* Should catch the overflow. */
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1);
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	/* And we will not have gone beyond. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* And further... */
+	KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src,
+					sizeof(pad.buf) + unconst + 2)
+				== pad.buf);
+	/* Should catch the overflow. */
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	/* And we will not have gone beyond. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+}
+
+static void strscpy_test(struct kunit *test)
+{
+	struct fortify_padding pad = { };
+	char src[] = "Copy me fully into a small buffer and I will overflow!";
+
+	/* Destination is %NUL-filled to start with. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_before, 0);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Legitimate strscpy() 1 less than of max size. */
+	KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src,
+				      sizeof(pad.buf) + unconst - 1),
+			-E2BIG);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Keeping space for %NUL, last two bytes should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	/* Legitimate max-size strscpy. */
+	KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src,
+				      sizeof(pad.buf) + unconst),
+			-E2BIG);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* A trailing %NUL will exist. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+
+	/* Now verify that FORTIFY is working... */
+	KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src,
+				      sizeof(pad.buf) + unconst + 1),
+			-E2BIG);
+	/* Should catch the overflow. */
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	/* And we will not have gone beyond. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* And much further... */
+	KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src,
+				      sizeof(src) * 2 + unconst),
+			-E2BIG);
+	/* Should catch the overflow. */
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	/* And we will not have gone beyond. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+}
+
+static void strcat_test(struct kunit *test)
+{
+	struct fortify_padding pad = { };
+	char src[sizeof(pad.buf) / 2] = { };
+	char one[] = "A";
+	char two[] = "BC";
+	int i;
+
+	/* Fill 15 bytes with valid characters. */
+	for (i = 0; i < sizeof(src) - 1; i++)
+		src[i] = i + 'A';
+
+	/* Destination is %NUL-filled to start with. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_before, 0);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Legitimate strcat() using less than half max size. */
+	KUNIT_ASSERT_TRUE(test, strcat(pad.buf, src) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Legitimate strcat() now 2 bytes shy of end. */
+	KUNIT_ASSERT_TRUE(test, strcat(pad.buf, src) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Last two bytes should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	/* Add one more character to the end. */
+	KUNIT_ASSERT_TRUE(test, strcat(pad.buf, one) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Last byte should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	/* And this one char will overflow. */
+	KUNIT_ASSERT_TRUE(test, strcat(pad.buf, one) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1);
+	/* Last byte should be %NUL thanks to FORTIFY. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* And adding two will overflow more. */
+	KUNIT_ASSERT_TRUE(test, strcat(pad.buf, two) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
+	/* Last byte should be %NUL thanks to FORTIFY. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+}
+
+static void strncat_test(struct kunit *test)
+{
+	struct fortify_padding pad = { };
+	char src[sizeof(pad.buf)] = { };
+	int i, partial;
+
+	/* Fill 31 bytes with valid characters. */
+	partial = sizeof(src) / 2 - 1;
+	for (i = 0; i < partial; i++)
+		src[i] = i + 'A';
+
+	/* Destination is %NUL-filled to start with. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_before, 0);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Legitimate strncat() using less than half max size. */
+	KUNIT_ASSERT_TRUE(test, strncat(pad.buf, src, partial) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Legitimate strncat() now 2 bytes shy of end. */
+	KUNIT_ASSERT_TRUE(test, strncat(pad.buf, src, partial) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Last two bytes should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	/* Add one more character to the end. */
+	KUNIT_ASSERT_TRUE(test, strncat(pad.buf, src, 1) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Last byte should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	/* And this one char will overflow. */
+	KUNIT_ASSERT_TRUE(test, strncat(pad.buf, src, 1) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1);
+	/* Last byte should be %NUL thanks to FORTIFY. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* And adding two will overflow more. */
+	KUNIT_ASSERT_TRUE(test, strncat(pad.buf, src, 2) == pad.buf);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
+	/* Last byte should be %NUL thanks to FORTIFY. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Force an unterminated destination, and overflow. */
+	pad.buf[sizeof(pad.buf) - 1] = 'A';
+	KUNIT_ASSERT_TRUE(test, strncat(pad.buf, src, 1) == pad.buf);
+	/* This will have tripped both strlen() and strcat(). */
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 3);
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	/* But we should not go beyond the end. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+}
+
+static void strlcat_test(struct kunit *test)
+{
+	struct fortify_padding pad = { };
+	char src[sizeof(pad.buf)] = { };
+	int i, partial;
+	int len = sizeof(pad.buf) + unconst;
+
+	/* Fill 15 bytes with valid characters. */
+	partial = sizeof(src) / 2 - 1;
+	for (i = 0; i < partial; i++)
+		src[i] = i + 'A';
+
+	/* Destination is %NUL-filled to start with. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_before, 0);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Legitimate strlcat() using less than half max size. */
+	KUNIT_ASSERT_EQ(test, strlcat(pad.buf, src, len), partial);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Legitimate strlcat() now 2 bytes shy of end. */
+	KUNIT_ASSERT_EQ(test, strlcat(pad.buf, src, len), partial * 2);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Last two bytes should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	/* Add one more character to the end. */
+	KUNIT_ASSERT_EQ(test, strlcat(pad.buf, "Q", len), partial * 2 + 1);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
+	/* Last byte should be %NUL */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+
+	/* And this one char will overflow. */
+	KUNIT_ASSERT_EQ(test, strlcat(pad.buf, "V", len * 2), len);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1);
+	/* Last byte should be %NUL thanks to FORTIFY. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* And adding two will overflow more. */
+	KUNIT_ASSERT_EQ(test, strlcat(pad.buf, "QQ", len * 2), len + 1);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
+	/* Last byte should be %NUL thanks to FORTIFY. */
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Force an unterminated destination, and overflow. */
+	pad.buf[sizeof(pad.buf) - 1] = 'A';
+	KUNIT_ASSERT_EQ(test, strlcat(pad.buf, "TT", len * 2), len + 2);
+	/* This will have tripped both strlen() and strlcat(). */
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+	KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+	/* But we should not go beyond the end. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+
+	/* Force an unterminated source, and overflow. */
+	memset(src, 'B', sizeof(src));
+	pad.buf[sizeof(pad.buf) - 1] = '\0';
+	KUNIT_ASSERT_EQ(test, strlcat(pad.buf, src, len * 3), len - 1 + sizeof(src));
+	/* This will have tripped both strlen() and strlcat(). */
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 3);
+	KUNIT_EXPECT_EQ(test, fortify_write_overflows, 3);
+	KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
+	/* But we should not go beyond the end. */
+	KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
+}
+
+static void memscan_test(struct kunit *test)
+{
+	char haystack[] = "Where oh where is my memory range?";
+	char *mem = haystack + strlen("Where oh where is ");
+	char needle = 'm';
+	size_t len = sizeof(haystack) + unconst;
+
+	KUNIT_ASSERT_PTR_EQ(test, memscan(haystack, needle, len),
+				  mem);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	/* Catch too-large range. */
+	KUNIT_ASSERT_PTR_EQ(test, memscan(haystack, needle, len + 1),
+				  NULL);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+	KUNIT_ASSERT_PTR_EQ(test, memscan(haystack, needle, len * 2),
+				  NULL);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+}
+
+static void memchr_test(struct kunit *test)
+{
+	char haystack[] = "Where oh where is my memory range?";
+	char *mem = haystack + strlen("Where oh where is ");
+	char needle = 'm';
+	size_t len = sizeof(haystack) + unconst;
+
+	KUNIT_ASSERT_PTR_EQ(test, memchr(haystack, needle, len),
+				  mem);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	/* Catch too-large range. */
+	KUNIT_ASSERT_PTR_EQ(test, memchr(haystack, needle, len + 1),
+				  NULL);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+	KUNIT_ASSERT_PTR_EQ(test, memchr(haystack, needle, len * 2),
+				  NULL);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+}
+
+static void memchr_inv_test(struct kunit *test)
+{
+	char haystack[] = "Where oh where is my memory range?";
+	char *mem = haystack + 1;
+	char needle = 'W';
+	size_t len = sizeof(haystack) + unconst;
+
+	/* Normal search is okay. */
+	KUNIT_ASSERT_PTR_EQ(test, memchr_inv(haystack, needle, len),
+				  mem);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	/* Catch too-large range. */
+	KUNIT_ASSERT_PTR_EQ(test, memchr_inv(haystack, needle, len + 1),
+				  NULL);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+	KUNIT_ASSERT_PTR_EQ(test, memchr_inv(haystack, needle, len * 2),
+				  NULL);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+}
+
+static void memcmp_test(struct kunit *test)
+{
+	char one[] = "My mind is going ...";
+	char two[] = "My mind is going ... I can feel it.";
+	size_t one_len = sizeof(one) + unconst - 1;
+	size_t two_len = sizeof(two) + unconst - 1;
+
+	/* We match the first string (ignoring the %NUL). */
+	KUNIT_ASSERT_EQ(test, memcmp(one, two, one_len), 0);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	/* Still in bounds, but no longer matching. */
+	KUNIT_ASSERT_EQ(test, memcmp(one, two, one_len + 1), -32);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+
+	/* Catch too-large ranges. */
+	KUNIT_ASSERT_EQ(test, memcmp(one, two, one_len + 2), INT_MIN);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+
+	KUNIT_ASSERT_EQ(test, memcmp(two, one, two_len + 2), INT_MIN);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+}
+
+static void kmemdup_test(struct kunit *test)
+{
+	char src[] = "I got Doom running on it!";
+	char *copy;
+	size_t len = sizeof(src) + unconst;
+
+	/* Copy is within bounds. */
+	copy = kmemdup(src, len, GFP_KERNEL);
+	KUNIT_EXPECT_NOT_NULL(test, copy);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	kfree(copy);
+
+	/* Without %NUL. */
+	copy = kmemdup(src, len - 1, GFP_KERNEL);
+	KUNIT_EXPECT_NOT_NULL(test, copy);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	kfree(copy);
+
+	/* Tiny bounds. */
+	copy = kmemdup(src, 1, GFP_KERNEL);
+	KUNIT_EXPECT_NOT_NULL(test, copy);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
+	kfree(copy);
+
+	/* Out of bounds by 1 byte. */
+	copy = kmemdup(src, len + 1, GFP_KERNEL);
+	KUNIT_EXPECT_NULL(test, copy);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 1);
+	kfree(copy);
+
+	/* Way out of bounds. */
+	copy = kmemdup(src, len * 2, GFP_KERNEL);
+	KUNIT_EXPECT_NULL(test, copy);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 2);
+	kfree(copy);
+
+	/* Starting offset causing out of bounds. */
+	copy = kmemdup(src + 1, len, GFP_KERNEL);
+	KUNIT_EXPECT_NULL(test, copy);
+	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 3);
+	kfree(copy);
+}
+
 static int fortify_test_init(struct kunit *test)
 {
 	if (!IS_ENABLED(CONFIG_FORTIFY_SOURCE))
@@ -373,6 +961,21 @@ static struct kunit_case fortify_test_cases[] = {
 	KUNIT_CASE(alloc_size_kvmalloc_dynamic_test),
 	KUNIT_CASE(alloc_size_devm_kmalloc_const_test),
 	KUNIT_CASE(alloc_size_devm_kmalloc_dynamic_test),
+	KUNIT_CASE(strlen_test),
+	KUNIT_CASE(strnlen_test),
+	KUNIT_CASE(strcpy_test),
+	KUNIT_CASE(strncpy_test),
+	KUNIT_CASE(strscpy_test),
+	KUNIT_CASE(strcat_test),
+	KUNIT_CASE(strncat_test),
+	KUNIT_CASE(strlcat_test),
+	/* skip memset: performs bounds checking on whole structs */
+	/* skip memcpy: still using warn-and-overwrite instead of hard-fail */
+	KUNIT_CASE(memscan_test),
+	KUNIT_CASE(memchr_test),
+	KUNIT_CASE(memchr_inv_test),
+	KUNIT_CASE(memcmp_test),
+	KUNIT_CASE(kmemdup_test),
 	{}
 };
 
-- 
2.34.1

[PATCH v3 5/5] fortify: Improve buffer overflow reporting

[Kees Cook]

Improve the reporting of buffer overflows under CONFIG_FORTIFY_SOURCE to
help accelerate debugging efforts. The calculations are all just sitting
in registers anyway, so pass them along to the function to be reported.

For example, before:

  detected buffer overflow in memcpy

and after:

  memcpy: detected buffer overflow: 4096 byte read of buffer size 1

Link: https://lore.kernel.org/r/20230407192717.636137-10-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/arm/boot/compressed/misc.c |  2 +-
 arch/x86/boot/compressed/misc.c |  2 +-
 include/linux/fortify-string.h  | 56 ++++++++++++++++++---------------
 lib/fortify_kunit.c             |  4 +--
 lib/string_helpers.c            |  9 +++---
 5 files changed, 39 insertions(+), 34 deletions(-)

diff --git a/arch/arm/boot/compressed/misc.c b/arch/arm/boot/compressed/misc.c
index d93e2e466f6a..6c41b270560e 100644
--- a/arch/arm/boot/compressed/misc.c
+++ b/arch/arm/boot/compressed/misc.c
@@ -154,7 +154,7 @@ decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p,
 		putstr(" done, booting the kernel.\n");
 }
 
-void __fortify_panic(const u8 reason)
+void __fortify_panic(const u8 reason, size_t avail, size_t size)
 {
 	error("detected buffer overflow");
 }
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index c9971b9dbb09..1844da203da9 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -496,7 +496,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
 	return output + entry_offset;
 }
 
-void __fortify_panic(const u8 reason)
+void __fortify_panic(const u8 reason, size_t avail, size_t size)
 {
 	error("detected buffer overflow");
 }
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index fbfb90479b8f..6aeebe0a6777 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -16,8 +16,8 @@
 					 FIELD_PREP(GENMASK(7, 1), func))
 
 #ifndef fortify_panic
-# define fortify_panic(func, write, retfail)	\
-	 __fortify_panic(FORTIFY_REASON(func, write))
+# define fortify_panic(func, write, avail, size, retfail)	\
+	 __fortify_panic(FORTIFY_REASON(func, write), avail, size)
 #endif
 
 #define FORTIFY_READ		 0
@@ -48,8 +48,8 @@ enum fortify_func {
 	EACH_FORTIFY_FUNC(MAKE_FORTIFY_FUNC)
 };
 
-void __fortify_report(const u8 reason);
-void __fortify_panic(const u8 reason) __cold __noreturn;
+void __fortify_report(const u8 reason, const size_t avail, const size_t size);
+void __fortify_panic(const u8 reason, const size_t avail, const size_t size) __cold __noreturn;
 void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)");
 void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");
 void __read_overflow2_field(size_t avail, size_t wanted) __compiletime_warning("detected read beyond size of field (2nd parameter); maybe use struct_group()?");
@@ -183,7 +183,7 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__write_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE, p);
+		fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE, p_size, size, p);
 	return __underlying_strncpy(p, q, size);
 }
 
@@ -214,7 +214,7 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size
 	/* Do not check characters beyond the end of p. */
 	ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
 	if (p_size <= ret && maxlen != ret)
-		fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ, ret);
+		fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ, p_size, ret + 1, ret);
 	return ret;
 }
 
@@ -250,7 +250,7 @@ __kernel_size_t __fortify_strlen(const char * const POS p)
 		return __underlying_strlen(p);
 	ret = strnlen(p, p_size);
 	if (p_size <= ret)
-		fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ, ret);
+		fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ, p_size, ret + 1, ret);
 	return ret;
 }
 
@@ -300,8 +300,8 @@ __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const PO
 	 * Generate a runtime write overflow error if len is greater than
 	 * p_size.
 	 */
-	if (len > p_size)
-		fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE, -E2BIG);
+	if (p_size < len)
+		fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE, p_size, len, -E2BIG);
 
 	/*
 	 * We can now safely call vanilla strscpy because we are protected from:
@@ -359,7 +359,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail)
 
 	/* Give up if string is already overflowed. */
 	if (p_size <= p_len)
-		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ, wanted);
+		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ, p_size, p_len + 1, wanted);
 
 	if (actual >= avail) {
 		copy_len = avail - p_len - 1;
@@ -368,7 +368,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail)
 
 	/* Give up if copy will overflow. */
 	if (p_size <= actual)
-		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE, wanted);
+		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE, p_size, actual + 1, wanted);
 	__underlying_memcpy(p + p_len, q, copy_len);
 	p[actual] = '\0';
 
@@ -395,9 +395,10 @@ __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
 char *strcat(char * const POS p, const char *q)
 {
 	const size_t p_size = __member_size(p);
+	const size_t wanted = strlcat(p, q, p_size);
 
-	if (strlcat(p, q, p_size) >= p_size)
-		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p);
+	if (p_size <= wanted)
+		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p_size, wanted + 1, p);
 	return p;
 }
 
@@ -426,14 +427,15 @@ char *strncat(char * const POS p, const char * const POS q, __kernel_size_t coun
 {
 	const size_t p_size = __member_size(p);
 	const size_t q_size = __member_size(q);
-	size_t p_len, copy_len;
+	size_t p_len, copy_len, total;
 
 	if (p_size == SIZE_MAX && q_size == SIZE_MAX)
 		return __underlying_strncat(p, q, count);
 	p_len = strlen(p);
 	copy_len = strnlen(q, count);
-	if (p_size < p_len + copy_len + 1)
-		fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE, p);
+	total = p_len + copy_len + 1;
+	if (p_size < total)
+		fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE, p_size, total, p);
 	__underlying_memcpy(p + p_len, q, copy_len);
 	p[p_len + copy_len] = '\0';
 	return p;
@@ -474,7 +476,7 @@ __FORTIFY_INLINE bool fortify_memset_chk(__kernel_size_t size,
 	 * lengths are unknown.)
 	 */
 	if (p_size != SIZE_MAX && p_size < size)
-		fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE, true);
+		fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE, p_size, size, true);
 	return false;
 }
 
@@ -574,9 +576,9 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
 	 * lengths are unknown.)
 	 */
 	if (p_size != SIZE_MAX && p_size < size)
-		fortify_panic(func, FORTIFY_WRITE, true);
+		fortify_panic(func, FORTIFY_WRITE, p_size, size, true);
 	else if (q_size != SIZE_MAX && q_size < size)
-		fortify_panic(func, FORTIFY_READ, true);
+		fortify_panic(func, FORTIFY_READ, p_size, size, true);
 
 	/*
 	 * Warn when writing beyond destination field size.
@@ -676,7 +678,7 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ, NULL);
+		fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ, p_size, size, NULL);
 	return __real_memscan(p, c, size);
 }
 
@@ -692,8 +694,10 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t
 		if (__compiletime_lessthan(q_size, size))
 			__read_overflow2();
 	}
-	if (p_size < size || q_size < size)
-		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, INT_MIN);
+	if (p_size < size)
+		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, p_size, size, INT_MIN);
+	else if (q_size < size)
+		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, q_size, size, INT_MIN);
 	return __underlying_memcmp(p, q, size);
 }
 
@@ -705,7 +709,7 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ, NULL);
+		fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ, p_size, size, NULL);
 	return __underlying_memchr(p, c, size);
 }
 
@@ -717,7 +721,7 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ, NULL);
+		fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ, p_size, size, NULL);
 	return __real_memchr_inv(p, c, size);
 }
 
@@ -730,7 +734,7 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp
 	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ, NULL);
+		fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ, p_size, size, NULL);
 	return __real_kmemdup(p, size, gfp);
 }
 
@@ -767,7 +771,7 @@ char *strcpy(char * const POS p, const char * const POS q)
 		__write_overflow();
 	/* Run-time check for dynamic size overflow. */
 	if (p_size < size)
-		fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE, p);
+		fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE, p_size, size, p);
 	__underlying_memcpy(p, q, size);
 	return p;
 }
diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
index f0accebeca02..493ec02dd5b3 100644
--- a/lib/fortify_kunit.c
+++ b/lib/fortify_kunit.c
@@ -17,8 +17,8 @@
 
 /* Redefine fortify_panic() to track failures. */
 void fortify_add_kunit_error(int write);
-#define fortify_panic(func, write, retfail) do {			\
-	__fortify_report(FORTIFY_REASON(func, write));			\
+#define fortify_panic(func, write, avail, size, retfail) do {		\
+	__fortify_report(FORTIFY_REASON(func, write), avail, size);	\
 	fortify_add_kunit_error(write);					\
 	return (retfail);						\
 } while (0)
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 5e53d42e32bb..5419282e12bd 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -1016,20 +1016,21 @@ static const char * const fortify_func_name[] = {
 #undef  MAKE_FORTIFY_FUNC_NAME
 };
 
-void __fortify_report(const u8 reason)
+void __fortify_report(const u8 reason, const size_t avail, const size_t size)
 {
 	const u8 func = FORTIFY_REASON_FUNC(reason);
 	const bool write = FORTIFY_REASON_DIR(reason);
 	const char *name;
 
 	name = fortify_func_name[umin(func, FORTIFY_FUNC_UNKNOWN)];
-	WARN(1, "%s: detected buffer %s overflow\n", name, str_read_write(!write));
+	WARN(1, "%s: detected buffer overflow: %zu byte %s of buffer size %zu\n",
+		 name, size, str_read_write(!write), avail);
 }
 EXPORT_SYMBOL(__fortify_report);
 
-void __fortify_panic(const u8 reason)
+void __fortify_panic(const u8 reason, const size_t avail, const size_t size)
 {
-	__fortify_report(reason);
+	__fortify_report(reason, avail, size);
 	BUG();
 }
 EXPORT_SYMBOL(__fortify_panic);
-- 
2.34.1