Re: [PATCH] string: Check for "nonstring" attribute on strscpy() arguments

[Przemek Kitszel <przemyslaw.kitszel@intel.com>]

On 8/5/24 23:43, Kees Cook wrote:
> 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@kernel.org>



> 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))

any way to avoid the usual caveat of repeating macro argument?

a variant of BUILD_BUG that is checking argument and otherwise pasting
it would nail it, but I didn't pondered how to implement such