GCC already checks for arguments that are marked with the "nonstring"[1] attribute when used on standard C String API functions (e.g. strcpy). Gain this compile-time checking also for the kernel's primary string copying function, strscpy(). Note that Clang has neither "nonstring" nor __builtin_has_attribute(). Link: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute [1] Signed-off-by: Kees Cook <kees@xxxxxxxxxx> --- Cc: Andy Shevchenko <andy@xxxxxxxxxx> Cc: Justin Stitt <justinstitt@xxxxxxxxxx> Cc: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Miguel Ojeda <ojeda@xxxxxxxxxx> Cc: Marco Elver <elver@xxxxxxxxxx> Cc: Nathan Chancellor <nathan@xxxxxxxxxx> Cc: Hao Luo <haoluo@xxxxxxxxxx> Cc: Przemek Kitszel <przemyslaw.kitszel@xxxxxxxxx> Cc: linux-sparse@xxxxxxxxxxxxxxx Cc: linux-hardening@xxxxxxxxxxxxxxx --- include/linux/compiler.h | 3 +++ include/linux/compiler_types.h | 7 +++++++ include/linux/string.h | 12 ++++++++---- 3 files changed, 18 insertions(+), 4 deletions(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 2df665fa2964..ec55bcce4146 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -242,6 +242,9 @@ static inline void *offset_to_ptr(const int *off) /* &a[0] degrades to a pointer: a different type from an array */ #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0])) +/* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */ +#define __must_be_cstr(p) BUILD_BUG_ON_ZERO(__annotated(p, nonstring)) + /* * This returns a constant expression while determining if an argument is * a constant expression, most importantly without evaluating the argument. diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index f14c275950b5..1a957ea2f4fe 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -421,6 +421,13 @@ struct ftrace_likely_data { #define __member_size(p) __builtin_object_size(p, 1) #endif +/* Determine if an attribute has been applied to a variable. */ +#if __has_builtin(__builtin_has_attribute) +#define __annotated(var, attr) __builtin_has_attribute(var, attr) +#else +#define __annotated(var, attr) (false) +#endif + /* * Some versions of gcc do not mark 'asm goto' volatile: * diff --git a/include/linux/string.h b/include/linux/string.h index 9edace076ddb..95b3fc308f4f 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -76,12 +76,16 @@ ssize_t sized_strscpy(char *, const char *, size_t); * known size. */ #define __strscpy0(dst, src, ...) \ - sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst)) -#define __strscpy1(dst, src, size) sized_strscpy(dst, src, size) + sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst) + \ + __must_be_cstr(dst) + __must_be_cstr(src)) +#define __strscpy1(dst, src, size) \ + sized_strscpy(dst, src, size + __must_be_cstr(dst) + __must_be_cstr(src)) #define __strscpy_pad0(dst, src, ...) \ - sized_strscpy_pad(dst, src, sizeof(dst) + __must_be_array(dst)) -#define __strscpy_pad1(dst, src, size) sized_strscpy_pad(dst, src, size) + sized_strscpy_pad(dst, src, sizeof(dst) + __must_be_array(dst) + \ + __must_be_cstr(dst) + __must_be_cstr(src)) +#define __strscpy_pad1(dst, src, size) \ + sized_strscpy_pad(dst, src, size + __must_be_cstr(dst) + __must_be_cstr(src)) /** * strscpy - Copy a C-string into a sized buffer -- 2.34.1
