From: Kees Cook Date: Thu, 6 Feb 2025 22:54:11 +0000 (-0800) Subject: compiler.h: Introduce __must_be_noncstr() X-Git-Tag: v6.15-rc1~233^2~12 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9f25b1fb1c93942af870428fa394b42fcda7572f;p=thirdparty%2Fkernel%2Flinux.git compiler.h: Introduce __must_be_noncstr() In preparation for adding more type checking to the memtostr/strtomem*() helpers, introduce the ability to check for the "nonstring" attribute. This is the reverse of what was added to strscpy*() in commit 559048d156ff ("string: Check for "nonstring" attribute on strscpy() arguments"). Note that __annotated() must be explicitly tested for, as GCC added __builtin_has_attribute() after it added the "nonstring" attribute. Do so here to avoid the !__annotated() test triggering build failures when __builtin_has_attribute() was missing but __nonstring was defined. (I've opted to squash this fix into this patch so we don't end up with a possible bisection target that would leave the kernel unbuildable.) Reported-by: Venkat Rao Bagalkote Reported-by: Stephen Rothwell Reported-by: Christophe Leroy Reported-by: Michael Kelley Closes: https://lore.kernel.org/all/adbe8dd1-a725-4811-ae7e-76fe770cf096@linux.vnet.ibm.com/ Tested-by: Michael Kelley Signed-off-by: Kees Cook --- diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 200fd3c5bc70d..d5201464c5e6d 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -206,9 +206,25 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, #define __must_be_byte_array(a) __BUILD_BUG_ON_ZERO_MSG(!__is_byte_array(a), \ "must be byte array") +/* + * If the "nonstring" attribute isn't available, we have to return true + * so the __must_*() checks pass when "nonstring" isn't supported. + */ +#if __has_attribute(__nonstring__) && defined(__annotated) +#define __is_cstr(a) (!__annotated(a, nonstring)) +#define __is_noncstr(a) (__annotated(a, nonstring)) +#else +#define __is_cstr(a) (true) +#define __is_noncstr(a) (true) +#endif + /* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */ #define __must_be_cstr(p) \ - __BUILD_BUG_ON_ZERO_MSG(__annotated(p, nonstring), "must be cstr (NUL-terminated)") + __BUILD_BUG_ON_ZERO_MSG(!__is_cstr(p), \ + "must be C-string (NUL-terminated)") +#define __must_be_noncstr(p) \ + __BUILD_BUG_ON_ZERO_MSG(!__is_noncstr(p), \ + "must be non-C-string (not NUL-terminated)") #endif /* __KERNEL__ */ diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 981cc3d7e3aa5..f59393464ea75 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -446,11 +446,14 @@ struct ftrace_likely_data { #define __member_size(p) __builtin_object_size(p, 1) #endif -/* Determine if an attribute has been applied to a variable. */ +/* + * Determine if an attribute has been applied to a variable. + * Using __annotated needs to check for __annotated being available, + * or negative tests may fail when annotation cannot be checked. For + * example, see the definition of __is_cstr(). + */ #if __has_builtin(__builtin_has_attribute) #define __annotated(var, attr) __builtin_has_attribute(var, attr) -#else -#define __annotated(var, attr) (false) #endif /*