@@ -63,6 +63,9 @@ extern int memcmp(const void *, const void *, size_t);
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
+
+#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
+
#endif
#endif
@@ -409,3 +409,8 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
debug_putstr("done.\nBooting the kernel.\n");
return output;
}
+
+void fortify_panic(const char *name)
+{
+ error("detected buffer overflow");
+}
@@ -77,6 +77,9 @@ int strcmp(const char *cs, const char *ct);
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
+
+#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
+
#endif
__must_check int memcpy_mcsafe_unrolled(void *dst, const void *src, size_t cnt);
@@ -169,4 +169,168 @@ static inline const char *kbasename(const char *path)
return tail ? tail + 1 : path;
}
+#define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline))
+#define __RENAME(x) __asm__(#x)
+
+void fortify_panic(const char *name) __noreturn __cold;
+void __buffer_overflow(void) __compiletime_error("buffer overflow");
+
+#if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE)
+__FORTIFY_INLINE char *strcpy(char *p, const char *q)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ size_t q_size = __builtin_object_size(q, 0);
+ if (p_size == (size_t)-1 && q_size == (size_t)-1)
+ return __builtin_strcpy(p, q);
+ if (strscpy(p, q, p_size < q_size ? p_size : q_size) < 0)
+ fortify_panic(__func__);
+ return p;
+}
+
+__FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ if (__builtin_constant_p(size) && p_size < size)
+ __buffer_overflow();
+ if (p_size < size)
+ fortify_panic(__func__);
+ return __builtin_strncpy(p, q, size);
+}
+
+__FORTIFY_INLINE char *strcat(char *p, const char *q)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ if (p_size == (size_t)-1)
+ return __builtin_strcat(p, q);
+ if (strlcat(p, q, p_size) >= p_size)
+ fortify_panic(__func__);
+ return p;
+}
+
+__FORTIFY_INLINE __kernel_size_t strlen(const char *p)
+{
+ __kernel_size_t ret;
+ size_t p_size = __builtin_object_size(p, 0);
+ if (p_size == (size_t)-1)
+ return __builtin_strlen(p);
+ ret = strnlen(p, p_size);
+ if (p_size <= ret)
+ fortify_panic(__func__);
+ return ret;
+}
+
+extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen);
+__FORTIFY_INLINE __kernel_size_t strnlen(const char *p, __kernel_size_t maxlen)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ __kernel_size_t ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
+ if (p_size <= ret)
+ fortify_panic(__func__);
+ return ret;
+}
+
+/* defined after fortified strlen and strnlen to reuse them */
+__FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count)
+{
+ size_t p_len, copy_len;
+ size_t p_size = __builtin_object_size(p, 0);
+ size_t q_size = __builtin_object_size(q, 0);
+ if (p_size == (size_t)-1 && q_size == (size_t)-1)
+ return __builtin_strncat(p, q, count);
+ p_len = strlen(p);
+ copy_len = strnlen(q, count);
+ if (p_size < p_len + copy_len + 1)
+ fortify_panic(__func__);
+ __builtin_memcpy(p + p_len, q, copy_len);
+ p[p_len + copy_len] = '\0';
+ return p;
+}
+
+__FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ if (__builtin_constant_p(size) && p_size < size)
+ __buffer_overflow();
+ if (p_size < size)
+ fortify_panic(__func__);
+ return __builtin_memset(p, c, size);
+}
+
+__FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ size_t q_size = __builtin_object_size(q, 0);
+ if (__builtin_constant_p(size) && (p_size < size || q_size < size))
+ __buffer_overflow();
+ if (p_size < size || q_size < size)
+ fortify_panic(__func__);
+ return __builtin_memcpy(p, q, size);
+}
+
+__FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ size_t q_size = __builtin_object_size(q, 0);
+ if (__builtin_constant_p(size) && (p_size < size || q_size < size))
+ __buffer_overflow();
+ if (p_size < size || q_size < size)
+ fortify_panic(__func__);
+ return __builtin_memmove(p, q, size);
+}
+
+extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
+__FORTIFY_INLINE void *memscan(void *p, int c, __kernel_size_t size)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ if (__builtin_constant_p(size) && p_size < size)
+ __buffer_overflow();
+ if (p_size < size)
+ fortify_panic(__func__);
+ return __real_memscan(p, c, size);
+}
+
+__FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ size_t q_size = __builtin_object_size(q, 0);
+ if (__builtin_constant_p(size) && (p_size < size || q_size < size))
+ __buffer_overflow();
+ if (p_size < size || q_size < size)
+ fortify_panic(__func__);
+ return __builtin_memcmp(p, q, size);
+}
+
+__FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ if (__builtin_constant_p(size) && p_size < size)
+ __buffer_overflow();
+ if (p_size < size)
+ fortify_panic(__func__);
+ return __builtin_memchr(p, c, size);
+}
+
+void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv);
+__FORTIFY_INLINE void *memchr_inv(const void *p, int c, size_t size)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ if (__builtin_constant_p(size) && p_size < size)
+ __buffer_overflow();
+ if (p_size < size)
+ fortify_panic(__func__);
+ return __real_memchr_inv(p, c, size);
+}
+
+extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup);
+__FORTIFY_INLINE void *kmemdup(const void *p, size_t size, gfp_t gfp)
+{
+ size_t p_size = __builtin_object_size(p, 0);
+ if (__builtin_constant_p(size) && p_size < size)
+ __buffer_overflow();
+ if (p_size < size)
+ fortify_panic(__func__);
+ return __real_kmemdup(p, size, gfp);
+}
+#endif
+
#endif /* _LINUX_STRING_H_ */
@@ -952,3 +952,9 @@ char *strreplace(char *s, char old, char new)
return s;
}
EXPORT_SYMBOL(strreplace);
+
+void fortify_panic(const char *name)
+{
+ panic("detected buffer overflow in %s", name);
+}
+EXPORT_SYMBOL(fortify_panic);
@@ -154,6 +154,12 @@ config HARDENED_USERCOPY_PAGESPAN
been removed. This config is intended to be used only while
trying to find such users.
+config FORTIFY_SOURCE
+ bool "Harden common functions against buffer overflows"
+ help
+ Detect overflows of buffers in common functions where the compiler
+ can determine the buffer size.
+
config STATIC_USERMODEHELPER
bool "Force all usermode helper calls through a single binary"
help
This adds support for compiling with a rough equivalent to the glibc _FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer overflow checks for string.h functions when the compiler determines the size of the source or destination buffer at compile-time. Unlike glibc, it covers buffer reads in addition to writes. GNU C __builtin_*_chk intrinsics are avoided because they would force a much more complex implementation. They aren't designed to detect read overflows and offer no real benefit when using an implementation based on inline checks. Inline checks don't add up to much code size and allow full use of the regular string intrinsics while avoiding the need for a bunch of _chk functions and per-arch assembly to avoid wrapper overhead. This detects various overflows at compile-time in various drivers and some non-x86 core kernel code. There will likely be issues caught in regular use at runtime too. Future improvements left out of initial implementation for simplicity, as it's all quite optional and can be done incrementally: * Some of the fortified string functions (strncpy, strcat), don't yet place a limit on reads from the source based on __builtin_object_size of the source buffer. * Extending coverage to more string functions (strlcpy, strlcat) and perhaps making the memory buffer checks into something more reusable for broader use. * It should be possible to optionally use __builtin_object_size(x, 1) for some functions (C strings) to detect intra-object overflows (like glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative approach to avoid likely compatibility issues. * The error reporting could be made friendlier by splitting up the compile-time error for reads and writes. * The compile-time checks should be made available via a separate config option which can be enabled by default (or always enabled) once enough time has passed to get the issues it catches fixed. Signed-off-by: Daniel Micay <danielmicay@gmail.com> --- Changes since v1: * fix compatibility with CONFIG_KASAN * replace strlcpy with strscpy in fortified strcpy and verify the source buffer * use fortified strlen/strnlen in fortified strncat to check for read overflow arch/arm64/include/asm/string.h | 3 + arch/x86/boot/compressed/misc.c | 5 ++ arch/x86/include/asm/string_64.h | 3 + include/linux/string.h | 164 +++++++++++++++++++++++++++++++++++++++ lib/string.c | 6 ++ security/Kconfig | 6 ++ 6 files changed, 187 insertions(+)