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Diffstat (limited to 'include/linux/fortify-string.h')
| -rw-r--r-- | include/linux/fortify-string.h | 624 |
1 files changed, 624 insertions, 0 deletions
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h new file mode 100644 index 000000000000..1067a8450826 --- /dev/null +++ b/include/linux/fortify-string.h @@ -0,0 +1,624 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_FORTIFY_STRING_H_ +#define _LINUX_FORTIFY_STRING_H_ + +#include <linux/bug.h> +#include <linux/const.h> +#include <linux/limits.h> + +#define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable +#define __RENAME(x) __asm__(#x) + +void fortify_panic(const char *name) __noreturn __cold; +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()?"); +void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)"); +void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("detected write beyond size of field (1st parameter); maybe use struct_group()?"); + +#define __compiletime_strlen(p) \ +({ \ + unsigned char *__p = (unsigned char *)(p); \ + size_t __ret = SIZE_MAX; \ + size_t __p_size = __member_size(p); \ + if (__p_size != SIZE_MAX && \ + __builtin_constant_p(*__p)) { \ + size_t __p_len = __p_size - 1; \ + if (__builtin_constant_p(__p[__p_len]) && \ + __p[__p_len] == '\0') \ + __ret = __builtin_strlen(__p); \ + } \ + __ret; \ +}) + +#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS) +extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr); +extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp); +extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy); +extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove); +extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset); +extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat); +extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy); +extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen); +extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat); +extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy); +#else + +#if defined(__SANITIZE_MEMORY__) +/* + * For KMSAN builds all memcpy/memset/memmove calls should be replaced by the + * corresponding __msan_XXX functions. + */ +#include <linux/kmsan_string.h> +#define __underlying_memcpy __msan_memcpy +#define __underlying_memmove __msan_memmove +#define __underlying_memset __msan_memset +#else +#define __underlying_memcpy __builtin_memcpy +#define __underlying_memmove __builtin_memmove +#define __underlying_memset __builtin_memset +#endif + +#define __underlying_memchr __builtin_memchr +#define __underlying_memcmp __builtin_memcmp +#define __underlying_strcat __builtin_strcat +#define __underlying_strcpy __builtin_strcpy +#define __underlying_strlen __builtin_strlen +#define __underlying_strncat __builtin_strncat +#define __underlying_strncpy __builtin_strncpy +#endif + +/** + * unsafe_memcpy - memcpy implementation with no FORTIFY bounds checking + * + * @dst: Destination memory address to write to + * @src: Source memory address to read from + * @bytes: How many bytes to write to @dst from @src + * @justification: Free-form text or comment describing why the use is needed + * + * This should be used for corner cases where the compiler cannot do the + * right thing, or during transitions between APIs, etc. It should be used + * very rarely, and includes a place for justification detailing where bounds + * checking has happened, and why existing solutions cannot be employed. + */ +#define unsafe_memcpy(dst, src, bytes, justification) \ + __underlying_memcpy(dst, src, bytes) + +/* + * Clang's use of __builtin_*object_size() within inlines needs hinting via + * __pass_*object_size(). The preference is to only ever use type 1 (member + * size, rather than struct size), but there remain some stragglers using + * type 0 that will be converted in the future. + */ +#define POS __pass_object_size(1) +#define POS0 __pass_object_size(0) +#define __struct_size(p) __builtin_object_size(p, 0) +#define __member_size(p) __builtin_object_size(p, 1) + +#define __compiletime_lessthan(bounds, length) ( \ + __builtin_constant_p((bounds) < (length)) && \ + (bounds) < (length) \ +) + +/** + * strncpy - Copy a string to memory with non-guaranteed NUL padding + * + * @p: pointer to destination of copy + * @q: pointer to NUL-terminated source string to copy + * @size: bytes to write at @p + * + * If strlen(@q) >= @size, the copy of @q will stop after @size bytes, + * and @p will NOT be NUL-terminated + * + * If strlen(@q) < @size, following the copy of @q, trailing NUL bytes + * will be written to @p until @size total bytes have been written. + * + * Do not use this function. While FORTIFY_SOURCE tries to avoid + * over-reads of @q, it cannot defend against writing unterminated + * results to @p. Using strncpy() remains ambiguous and fragile. + * Instead, please choose an alternative, so that the expectation + * of @p's contents is unambiguous: + * + * +--------------------+-----------------+------------+ + * | @p needs to be: | padded to @size | not padded | + * +====================+=================+============+ + * | NUL-terminated | strscpy_pad() | strscpy() | + * +--------------------+-----------------+------------+ + * | not NUL-terminated | strtomem_pad() | strtomem() | + * +--------------------+-----------------+------------+ + * + * Note strscpy*()'s differing return values for detecting truncation, + * and strtomem*()'s expectation that the destination is marked with + * __nonstring when it is a character array. + * + */ +__FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3) +char *strncpy(char * const POS p, const char *q, __kernel_size_t size) +{ + size_t p_size = __member_size(p); + + if (__compiletime_lessthan(p_size, size)) + __write_overflow(); + if (p_size < size) + fortify_panic(__func__); + return __underlying_strncpy(p, q, size); +} + +__FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2) +char *strcat(char * const POS p, const char *q) +{ + size_t p_size = __member_size(p); + + if (p_size == SIZE_MAX) + return __underlying_strcat(p, q); + if (strlcat(p, q, p_size) >= p_size) + fortify_panic(__func__); + return p; +} + +extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen); +__FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size_t maxlen) +{ + size_t p_size = __member_size(p); + size_t p_len = __compiletime_strlen(p); + size_t ret; + + /* We can take compile-time actions when maxlen is const. */ + if (__builtin_constant_p(maxlen) && p_len != SIZE_MAX) { + /* If p is const, we can use its compile-time-known len. */ + if (maxlen >= p_size) + return p_len; + } + + /* 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__); + return ret; +} + +/* + * Defined after fortified strnlen to reuse it. However, it must still be + * possible for strlen() to be used on compile-time strings for use in + * static initializers (i.e. as a constant expression). + */ +#define strlen(p) \ + __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)), \ + __builtin_strlen(p), __fortify_strlen(p)) +__FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1) +__kernel_size_t __fortify_strlen(const char * const POS p) +{ + __kernel_size_t ret; + size_t p_size = __member_size(p); + + /* Give up if we don't know how large p is. */ + if (p_size == SIZE_MAX) + return __underlying_strlen(p); + ret = strnlen(p, p_size); + if (p_size <= ret) + fortify_panic(__func__); + return ret; +} + +/* defined after fortified strlen to reuse it */ +extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy); +__FORTIFY_INLINE size_t strlcpy(char * const POS p, const char * const POS q, size_t size) +{ + size_t p_size = __member_size(p); + size_t q_size = __member_size(q); + size_t q_len; /* Full count of source string length. */ + size_t len; /* Count of characters going into destination. */ + + if (p_size == SIZE_MAX && q_size == SIZE_MAX) + return __real_strlcpy(p, q, size); + q_len = strlen(q); + len = (q_len >= size) ? size - 1 : q_len; + if (__builtin_constant_p(size) && __builtin_constant_p(q_len) && size) { + /* Write size is always larger than destination. */ + if (len >= p_size) + __write_overflow(); + } + if (size) { + if (len >= p_size) + fortify_panic(__func__); + __underlying_memcpy(p, q, len); + p[len] = '\0'; + } + return q_len; +} + +/* defined after fortified strnlen to reuse it */ +extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy); +__FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, size_t size) +{ + size_t len; + /* Use string size rather than possible enclosing struct size. */ + size_t p_size = __member_size(p); + size_t q_size = __member_size(q); + + /* If we cannot get size of p and q default to call strscpy. */ + if (p_size == SIZE_MAX && q_size == SIZE_MAX) + return __real_strscpy(p, q, size); + + /* + * If size can be known at compile time and is greater than + * p_size, generate a compile time write overflow error. + */ + if (__compiletime_lessthan(p_size, size)) + __write_overflow(); + + /* + * This call protects from read overflow, because len will default to q + * length if it smaller than size. + */ + len = strnlen(q, size); + /* + * If len equals size, we will copy only size bytes which leads to + * -E2BIG being returned. + * Otherwise we will copy len + 1 because of the final '\O'. + */ + len = len == size ? size : len + 1; + + /* + * Generate a runtime write overflow error if len is greater than + * p_size. + */ + if (len > p_size) + fortify_panic(__func__); + + /* + * We can now safely call vanilla strscpy because we are protected from: + * 1. Read overflow thanks to call to strnlen(). + * 2. Write overflow thanks to above ifs. + */ + return __real_strscpy(p, q, len); +} + +/* defined after fortified strlen and strnlen to reuse them */ +__FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3) +char *strncat(char * const POS p, const char * const POS q, __kernel_size_t count) +{ + size_t p_len, copy_len; + size_t p_size = __member_size(p); + size_t q_size = __member_size(q); + + 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(__func__); + __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, + const size_t p_size, + const size_t p_size_field) +{ + if (__builtin_constant_p(size)) { + /* + * Length argument is a constant expression, so we + * can perform compile-time bounds checking where + * buffer sizes are also known at compile time. + */ + + /* Error when size is larger than enclosing struct. */ + if (__compiletime_lessthan(p_size_field, p_size) && + __compiletime_lessthan(p_size, size)) + __write_overflow(); + + /* Warn when write size is larger than dest field. */ + if (__compiletime_lessthan(p_size_field, size)) + __write_overflow_field(p_size_field, size); + } + /* + * At this point, length argument may not be a constant expression, + * so run-time bounds checking can be done where buffer sizes are + * known. (This is not an "else" because the above checks may only + * be compile-time warnings, and we want to still warn for run-time + * overflows.) + */ + + /* + * Always stop accesses beyond the struct that contains the + * field, when the buffer's remaining size is known. + * (The SIZE_MAX test is to optimize away checks where the buffer + * lengths are unknown.) + */ + if (p_size != SIZE_MAX && p_size < size) + fortify_panic("memset"); +} + +#define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({ \ + size_t __fortify_size = (size_t)(size); \ + fortify_memset_chk(__fortify_size, p_size, p_size_field), \ + __underlying_memset(p, c, __fortify_size); \ +}) + +/* + * __struct_size() vs __member_size() must be captured here to avoid + * evaluating argument side-effects further into the macro layers. + */ +#ifndef CONFIG_KMSAN +#define memset(p, c, s) __fortify_memset_chk(p, c, s, \ + __struct_size(p), __member_size(p)) +#endif + +/* + * To make sure the compiler can enforce protection against buffer overflows, + * memcpy(), memmove(), and memset() must not be used beyond individual + * struct members. If you need to copy across multiple members, please use + * struct_group() to create a named mirror of an anonymous struct union. + * (e.g. see struct sk_buff.) Read overflow checking is currently only + * done when a write overflow is also present, or when building with W=1. + * + * Mitigation coverage matrix + * Bounds checking at: + * +-------+-------+-------+-------+ + * | Compile time | Run time | + * memcpy() argument sizes: | write | read | write | read | + * dest source length +-------+-------+-------+-------+ + * memcpy(known, known, constant) | y | y | n/a | n/a | + * memcpy(known, unknown, constant) | y | n | n/a | V | + * memcpy(known, known, dynamic) | n | n | B | B | + * memcpy(known, unknown, dynamic) | n | n | B | V | + * memcpy(unknown, known, constant) | n | y | V | n/a | + * memcpy(unknown, unknown, constant) | n | n | V | V | + * memcpy(unknown, known, dynamic) | n | n | V | B | + * memcpy(unknown, unknown, dynamic) | n | n | V | V | + * +-------+-------+-------+-------+ + * + * y = perform deterministic compile-time bounds checking + * n = cannot perform deterministic compile-time bounds checking + * n/a = no run-time bounds checking needed since compile-time deterministic + * B = can perform run-time bounds checking (currently unimplemented) + * V = vulnerable to run-time overflow (will need refactoring to solve) + * + */ +__FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, + const size_t p_size, + const size_t q_size, + const size_t p_size_field, + const size_t q_size_field, + const char *func) +{ + if (__builtin_constant_p(size)) { + /* + * Length argument is a constant expression, so we + * can perform compile-time bounds checking where + * buffer sizes are also known at compile time. + */ + + /* Error when size is larger than enclosing struct. */ + if (__compiletime_lessthan(p_size_field, p_size) && + __compiletime_lessthan(p_size, size)) + __write_overflow(); + if (__compiletime_lessthan(q_size_field, q_size) && + __compiletime_lessthan(q_size, size)) + __read_overflow2(); + + /* Warn when write size argument larger than dest field. */ + if (__compiletime_lessthan(p_size_field, size)) + __write_overflow_field(p_size_field, size); + /* + * Warn for source field over-read when building with W=1 + * or when an over-write happened, so both can be fixed at + * the same time. + */ + if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || + __compiletime_lessthan(p_size_field, size)) && + __compiletime_lessthan(q_size_field, size)) + __read_overflow2_field(q_size_field, size); + } + /* + * At this point, length argument may not be a constant expression, + * so run-time bounds checking can be done where buffer sizes are + * known. (This is not an "else" because the above checks may only + * be compile-time warnings, and we want to still warn for run-time + * overflows.) + */ + + /* + * Always stop accesses beyond the struct that contains the + * field, when the buffer's remaining size is known. + * (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); + + /* + * Warn when writing beyond destination field size. + * + * We must ignore p_size_field == 0 for existing 0-element + * fake flexible arrays, until they are all converted to + * proper flexible arrays. + * + * The implementation of __builtin_*object_size() behaves + * like sizeof() when not directly referencing a flexible + * array member, which means there will be many bounds checks + * that will appear at run-time, without a way for them to be + * detected at compile-time (as can be done when the destination + * is specifically the flexible array member). + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101832 + */ + if (p_size_field != 0 && p_size_field != SIZE_MAX && + p_size != p_size_field && p_size_field < size) + return true; + + return false; +} + +#define __fortify_memcpy_chk(p, q, size, p_size, q_size, \ + p_size_field, q_size_field, op) ({ \ + const size_t __fortify_size = (size_t)(size); \ + const size_t __p_size = (p_size); \ + const size_t __q_size = (q_size); \ + const size_t __p_size_field = (p_size_field); \ + 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), \ + #op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \ + __fortify_size, \ + "field \"" #p "\" at " __FILE__ ":" __stringify(__LINE__), \ + __p_size_field); \ + __underlying_##op(p, q, __fortify_size); \ +}) + +/* + * Notes about compile-time buffer size detection: + * + * With these types... + * + * struct middle { + * u16 a; + * u8 middle_buf[16]; + * int b; + * }; + * struct end { + * u16 a; + * u8 end_buf[16]; + * }; + * struct flex { + * int a; + * u8 flex_buf[]; + * }; + * + * void func(TYPE *ptr) { ... } + * + * Cases where destination size cannot be currently detected: + * - the size of ptr's object (seemingly by design, gcc & clang fail): + * __builtin_object_size(ptr, 1) == SIZE_MAX + * - the size of flexible arrays in ptr's obj (by design, dynamic size): + * __builtin_object_size(ptr->flex_buf, 1) == SIZE_MAX + * - the size of ANY array at the end of ptr's obj (gcc and clang bug): + * __builtin_object_size(ptr->end_buf, 1) == SIZE_MAX + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836 + * + * Cases where destination size is currently detected: + * - the size of non-array members within ptr's object: + * __builtin_object_size(ptr->a, 1) == 2 + * - the size of non-flexible-array in the middle of ptr's obj: + * __builtin_object_size(ptr->middle_buf, 1) == 16 + * + */ + +/* + * __struct_size() vs __member_size() must be captured here to avoid + * evaluating argument side-effects further into the macro layers. + */ +#define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ + __struct_size(p), __struct_size(q), \ + __member_size(p), __member_size(q), \ + memcpy) +#define memmove(p, q, s) __fortify_memcpy_chk(p, q, s, \ + __struct_size(p), __struct_size(q), \ + __member_size(p), __member_size(q), \ + memmove) + +extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); +__FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size) +{ + size_t p_size = __struct_size(p); + + if (__compiletime_lessthan(p_size, size)) + __read_overflow(); + if (p_size < size) + fortify_panic(__func__); + return __real_memscan(p, c, size); +} + +__FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3) +int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t size) +{ + size_t p_size = __struct_size(p); + size_t q_size = __struct_size(q); + + if (__builtin_constant_p(size)) { + if (__compiletime_lessthan(p_size, size)) + __read_overflow(); + if (__compiletime_lessthan(q_size, size)) + __read_overflow2(); + } + if (p_size < size || q_size < size) + fortify_panic(__func__); + return __underlying_memcmp(p, q, size); +} + +__FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3) +void *memchr(const void * const POS0 p, int c, __kernel_size_t size) +{ + size_t p_size = __struct_size(p); + + if (__compiletime_lessthan(p_size, size)) + __read_overflow(); + if (p_size < size) + fortify_panic(__func__); + return __underlying_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 * const POS0 p, int c, size_t size) +{ + size_t p_size = __struct_size(p); + + if (__compiletime_lessthan(p_size, size)) + __read_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 * const POS0 p, size_t size, gfp_t gfp) +{ + size_t p_size = __struct_size(p); + + if (__compiletime_lessthan(p_size, size)) + __read_overflow(); + if (p_size < size) + fortify_panic(__func__); + return __real_kmemdup(p, size, gfp); +} + +/* Defined after fortified strlen to reuse it. */ +__FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2) +char *strcpy(char * const POS p, const char * const POS q) +{ + size_t p_size = __member_size(p); + size_t q_size = __member_size(q); + size_t size; + + /* If neither buffer size is known, immediately give up. */ + if (__builtin_constant_p(p_size) && + __builtin_constant_p(q_size) && + p_size == SIZE_MAX && q_size == SIZE_MAX) + return __underlying_strcpy(p, q); + size = strlen(q) + 1; + /* Compile-time check for const size overflow. */ + if (__compiletime_lessthan(p_size, size)) + __write_overflow(); + /* Run-time check for dynamic size overflow. */ + if (p_size < size) + fortify_panic(__func__); + __underlying_memcpy(p, q, size); + return p; +} + +/* Don't use these outside the FORITFY_SOURCE implementation */ +#undef __underlying_memchr +#undef __underlying_memcmp +#undef __underlying_strcat +#undef __underlying_strcpy +#undef __underlying_strlen +#undef __underlying_strncat +#undef __underlying_strncpy + +#undef POS +#undef POS0 + +#endif /* _LINUX_FORTIFY_STRING_H_ */ |