| Message ID | 20240805214340.work.339-kees@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | string: Check for "nonstring" attribute on strscpy() arguments | expand |
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
On Mon, Aug 5, 2024 at 11:43 PM Kees Cook <kees@kernel.org> wrote: > > +/* 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 `__annotated` is obviously best-effort given this definition, and we do similar things elsewhere, and it has a double-underscore. However, I wonder if this being a "query" (vs. something like an attribute) may imply that it has a greater risk of someone thinking it will always reply with the right answer... (if e.g. they copy-paste another use). Perhaps there is a more explicit name to let users recall that. Anyway, it looks sensible to me: more compile-time checking seldomly hurts (apart from complexity in these definitions :). So: Reviewed-by: Miguel Ojeda <ojeda@kernel.org> I also introduced a mistake on purpose and I got the expected build error, so: Tested-by: Miguel Ojeda <ojeda@kernel.org> Cheers, Miguel
On Tue, Aug 06, 2024 at 12:29:30PM +0200, Przemek Kitszel wrote: > 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 The use of __must_be_cstr() shouldn't cause side-effects, so from what I can tell this is all okay. And since BUILD_BUG_ON_ZERO() resolves to a constant expression, it shouldn't change the processing of the "size" argument in the strscpy internals...
On Mon, 05 Aug 2024 14:43:44 -0700, 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(). > > [...] Applied to for-next/hardening, thanks! [1/1] string: Check for "nonstring" attribute on strscpy() arguments https://git.kernel.org/kees/c/559048d156ff Take care,
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
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> --- Cc: Andy Shevchenko <andy@kernel.org> Cc: Justin Stitt <justinstitt@google.com> Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Miguel Ojeda <ojeda@kernel.org> Cc: Marco Elver <elver@google.com> Cc: Nathan Chancellor <nathan@kernel.org> Cc: Hao Luo <haoluo@google.com> Cc: Przemek Kitszel <przemyslaw.kitszel@intel.com> Cc: linux-sparse@vger.kernel.org Cc: linux-hardening@vger.kernel.org --- include/linux/compiler.h | 3 +++ include/linux/compiler_types.h | 7 +++++++ include/linux/string.h | 12 ++++++++---- 3 files changed, 18 insertions(+), 4 deletions(-)