From: Kees Cook <[email protected]> Sent: Friday, February 28, 2025 9:42 AM > > 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 <[email protected]> > Reported-by: Stephen Rothwell <[email protected]> > Reported-by: Christophe Leroy <[email protected]> > Reported-by: Michael Kelley <[email protected]> > Closes: > https://lore.kernel.org/all/[email protected]/ > > Signed-off-by: Kees Cook <[email protected]> > --- > include/linux/compiler.h | 18 +++++++++++++++++- > include/linux/compiler_types.h | 9 ++++++--- > 2 files changed, 23 insertions(+), 4 deletions(-) > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > index 200fd3c5bc70..d5201464c5e6 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 981cc3d7e3aa..f59393464ea7 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 > > /* > -- > 2.34.1 >
Compile tested on x86 with gcc 9.4.0, and it resolves the compile problem I was originally seeing with linux-next-20250226. Tested-by: Michael Kelley <[email protected]>
