Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH v6 4/4] fortify: Add Clang support | Date | Thu, 3 Feb 2022 09:33:07 -0800 |
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Enable FORTIFY_SOURCE support for Clang:
Use the new __pass_object_size and __overloadable attributes so that Clang will have appropriate visibility into argument sizes such that __builtin_object_size(p, 1) will behave correctly. Additional details here: https://github.com/llvm/llvm-project/issues/53516 https://github.com/ClangBuiltLinux/linux/issues/1401
When available, use the new __diagnose_as attribute to make sure no compile-time diagnostic warnings are lost due to the effectively renamed string functions.
Redefine strlen() as a macro that tests for being a constant expression so that strlen() can still be used in static initializers, which was lost when adding __pass_object_size and __overloadable.
Finally, a bug with __builtin_constant_p() of globally defined variables was fixed in Clang 13 (and backported to 12.0.1), so FORTIFY support must depend on that version or later. Additional details here: https://bugs.llvm.org/show_bug.cgi?id=41459 commit a52f8a59aef4 ("fortify: Explicitly disable Clang support")
Cc: Miguel Ojeda <ojeda@kernel.org> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Nathan Chancellor <nathan@kernel.org> Cc: George Burgess IV <gbiv@google.com> Cc: llvm@lists.linux.dev Signed-off-by: Kees Cook <keescook@chromium.org> --- include/linux/fortify-string.h | 58 +++++++++++++++++++++++++--------- security/Kconfig | 3 +- 2 files changed, 44 insertions(+), 17 deletions(-)
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index c45159dbdaa1..2ffe4f2f79eb 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -2,7 +2,9 @@ #ifndef _LINUX_FORTIFY_STRING_H_ #define _LINUX_FORTIFY_STRING_H_ -#define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline)) +#include <linux/const.h> + +#define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline)) __overloadable #define __RENAME(x) __asm__(#x) void fortify_panic(const char *name) __noreturn __cold; @@ -50,7 +52,17 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) #define __underlying_strncpy __builtin_strncpy #endif -__FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) +/* + * 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) + +__FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3) +char *strncpy(char * POS p, const char *q, __kernel_size_t size) { size_t p_size = __builtin_object_size(p, 1); @@ -61,7 +73,8 @@ __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) return __underlying_strncpy(p, q, size); } -__FORTIFY_INLINE char *strcat(char *p, const char *q) +__FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2) +char *strcat(char * POS p, const char *q) { size_t p_size = __builtin_object_size(p, 1); @@ -73,7 +86,7 @@ __FORTIFY_INLINE char *strcat(char *p, const char *q) } 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) +__FORTIFY_INLINE __kernel_size_t strnlen(const char * POS p, __kernel_size_t maxlen) { size_t p_size = __builtin_object_size(p, 1); size_t p_len = __compiletime_strlen(p); @@ -93,8 +106,16 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char *p, __kernel_size_t maxlen) return ret; } -/* defined after fortified strnlen to reuse it. */ -__FORTIFY_INLINE __kernel_size_t strlen(const char *p) +/* + * 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 * POS p) { __kernel_size_t ret; size_t p_size = __builtin_object_size(p, 1); @@ -110,7 +131,7 @@ __FORTIFY_INLINE __kernel_size_t strlen(const char *p) /* 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 *p, const char *q, size_t size) +__FORTIFY_INLINE size_t strlcpy(char * POS p, const char * POS q, size_t size) { size_t p_size = __builtin_object_size(p, 1); size_t q_size = __builtin_object_size(q, 1); @@ -137,7 +158,7 @@ __FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size) /* 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 *p, const char *q, size_t size) +__FORTIFY_INLINE ssize_t strscpy(char * POS p, const char * POS q, size_t size) { size_t len; /* Use string size rather than possible enclosing struct size. */ @@ -183,7 +204,8 @@ __FORTIFY_INLINE ssize_t strscpy(char *p, const char *q, size_t size) } /* defined after fortified strlen and strnlen to reuse them */ -__FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count) +__FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3) +char *strncat(char * POS p, const char * POS q, __kernel_size_t count) { size_t p_len, copy_len; size_t p_size = __builtin_object_size(p, 1); @@ -354,7 +376,7 @@ __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size, memmove) extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); -__FORTIFY_INLINE void *memscan(void *p, int c, __kernel_size_t size) +__FORTIFY_INLINE void *memscan(void * POS0 p, int c, __kernel_size_t size) { size_t p_size = __builtin_object_size(p, 0); @@ -365,7 +387,8 @@ __FORTIFY_INLINE void *memscan(void *p, int c, __kernel_size_t size) return __real_memscan(p, c, size); } -__FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) +__FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3) +int memcmp(const void * POS0 p, const void * POS0 q, __kernel_size_t size) { size_t p_size = __builtin_object_size(p, 0); size_t q_size = __builtin_object_size(q, 0); @@ -381,7 +404,8 @@ __FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) return __underlying_memcmp(p, q, size); } -__FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) +__FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3) +void *memchr(const void * POS0 p, int c, __kernel_size_t size) { size_t p_size = __builtin_object_size(p, 0); @@ -393,7 +417,7 @@ __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t 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) +__FORTIFY_INLINE void *memchr_inv(const void * POS0 p, int c, size_t size) { size_t p_size = __builtin_object_size(p, 0); @@ -405,7 +429,7 @@ __FORTIFY_INLINE void *memchr_inv(const void *p, int c, size_t 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) +__FORTIFY_INLINE void *kmemdup(const void * POS0 p, size_t size, gfp_t gfp) { size_t p_size = __builtin_object_size(p, 0); @@ -417,7 +441,8 @@ __FORTIFY_INLINE void *kmemdup(const void *p, size_t size, gfp_t gfp) } /* Defined after fortified strlen to reuse it. */ -__FORTIFY_INLINE char *strcpy(char *p, const char *q) +__FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2) +char *strcpy(char * POS p, const char * POS q) { size_t p_size = __builtin_object_size(p, 1); size_t q_size = __builtin_object_size(q, 1); @@ -446,4 +471,7 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q) #undef __underlying_strncat #undef __underlying_strncpy +#undef POS0 +#undef POS + #endif /* _LINUX_FORTIFY_STRING_H_ */ diff --git a/security/Kconfig b/security/Kconfig index 0b847f435beb..c125026ed088 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -177,9 +177,8 @@ config HARDENED_USERCOPY_PAGESPAN config FORTIFY_SOURCE bool "Harden common str/mem functions against buffer overflows" depends on ARCH_HAS_FORTIFY_SOURCE - # https://bugs.llvm.org/show_bug.cgi?id=50322 # https://bugs.llvm.org/show_bug.cgi?id=41459 - depends on !CC_IS_CLANG + depends on !CC_IS_CLANG || CLANG_VERSION >= 120001 help Detect overflows of buffers in common string and memory functions where the compiler can determine and validate the buffer sizes. -- 2.30.2
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