| Message ID | 20220208225350.1331628-8-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 67ebc3ab446230c77fe3b545a9d8a11cac1cfb6e |
| Headers | show |
| Series | fortify: Add Clang support | expand |
On Tue, Feb 8, 2022 at 2:53 PM Kees Cook <keescook@chromium.org> wrote: > > In preparation for enabling Clang FORTIFY_SOURCE support, redefine > strlen() as a macro that tests for being a constant expression > so that strlen() can still be used in static initializers, which is > lost when adding __pass_object_size and __overloadable. > > An example of this usage can be seen here: > https://lore.kernel.org/all/202201252321.dRmWZ8wW-lkp@intel.com/ > > Notably, this constant expression feature of strlen() is not available > for architectures that build with -ffreestanding. This means the kernel > currently does not universally expect strlen() to be used this way, but > since there _are_ some build configurations that depend on it, retain > the characteristic for Clang FORTIFY_SOURCE builds too. > > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > include/linux/fortify-string.h | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h > index db1ad1c1c79a..f77cf22e2d60 100644 > --- a/include/linux/fortify-string.h > +++ b/include/linux/fortify-string.h > @@ -2,6 +2,8 @@ > #ifndef _LINUX_FORTIFY_STRING_H_ > #define _LINUX_FORTIFY_STRING_H_ > > +#include <linux/const.h> > + > #define __FORTIFY_INLINE extern __always_inline __gnu_inline > #define __RENAME(x) __asm__(#x) > > @@ -95,9 +97,16 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const p, __kernel_size_t m > return ret; > } > > -/* defined after fortified strnlen to reuse it. */ > +/* > + * Defined after fortified strnlen to reuse it. However, it must still be > + * possible for strlen() to be used on compile-time strings for use in > + * static initializers (i.e. as a constant expression). > + */ > +#define strlen(p) \ > + __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)), \ Is `__is_constexpr(p) == __is_constexpr(__builtin_strlen(p))`? i.e. can we drop the first `__builtin_strlen`? It seems redundant. So instead, we'd have: #define strlen(p) __builtin_choose_expr(__is_constexpr(p), __builtin_strlen(p), __fortify_strlen(p)) Or is there some funny business where p isn't constexpr but strlen(p) somehow is? I doubt that. (Or is it that p is constexpr, but strlen(p) is not?) (Guess I'm wrong: https://godbolt.org/z/19ffz7vjx) Ok then. Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > + __builtin_strlen(p), __fortify_strlen(p)) > __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1) > -__kernel_size_t strlen(const char * const p) > +__kernel_size_t __fortify_strlen(const char * const p) > { > __kernel_size_t ret; > size_t p_size = __builtin_object_size(p, 1); > -- > 2.30.2 >
On Tue, Feb 08, 2022 at 03:17:13PM -0800, Nick Desaulniers wrote: > On Tue, Feb 8, 2022 at 2:53 PM Kees Cook <keescook@chromium.org> wrote: > > > > In preparation for enabling Clang FORTIFY_SOURCE support, redefine > > strlen() as a macro that tests for being a constant expression > > so that strlen() can still be used in static initializers, which is > > lost when adding __pass_object_size and __overloadable. > > > > An example of this usage can be seen here: > > https://lore.kernel.org/all/202201252321.dRmWZ8wW-lkp@intel.com/ > > > > Notably, this constant expression feature of strlen() is not available > > for architectures that build with -ffreestanding. This means the kernel > > currently does not universally expect strlen() to be used this way, but > > since there _are_ some build configurations that depend on it, retain > > the characteristic for Clang FORTIFY_SOURCE builds too. > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > --- > > include/linux/fortify-string.h | 13 +++++++++++-- > > 1 file changed, 11 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h > > index db1ad1c1c79a..f77cf22e2d60 100644 > > --- a/include/linux/fortify-string.h > > +++ b/include/linux/fortify-string.h > > @@ -2,6 +2,8 @@ > > #ifndef _LINUX_FORTIFY_STRING_H_ > > #define _LINUX_FORTIFY_STRING_H_ > > > > +#include <linux/const.h> > > + > > #define __FORTIFY_INLINE extern __always_inline __gnu_inline > > #define __RENAME(x) __asm__(#x) > > > > @@ -95,9 +97,16 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const p, __kernel_size_t m > > return ret; > > } > > > > -/* defined after fortified strnlen to reuse it. */ > > +/* > > + * Defined after fortified strnlen to reuse it. However, it must still be > > + * possible for strlen() to be used on compile-time strings for use in > > + * static initializers (i.e. as a constant expression). > > + */ > > +#define strlen(p) \ > > + __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)), \ > > Is `__is_constexpr(p) == __is_constexpr(__builtin_strlen(p))`? i.e. > can we drop the first `__builtin_strlen`? It seems redundant. > > So instead, we'd have: > > #define strlen(p) __builtin_choose_expr(__is_constexpr(p), > __builtin_strlen(p), __fortify_strlen(p)) > > Or is there some funny business where p isn't constexpr but strlen(p) > somehow is? I doubt that. (Or is it that p is constexpr, but > strlen(p) is not?) > > (Guess I'm wrong: https://godbolt.org/z/19ffz7vjx) Yeah, as you've discovered ... funny business. :P > Ok then. > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Thanks!
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index db1ad1c1c79a..f77cf22e2d60 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -2,6 +2,8 @@ #ifndef _LINUX_FORTIFY_STRING_H_ #define _LINUX_FORTIFY_STRING_H_ +#include <linux/const.h> + #define __FORTIFY_INLINE extern __always_inline __gnu_inline #define __RENAME(x) __asm__(#x) @@ -95,9 +97,16 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const p, __kernel_size_t m return ret; } -/* defined after fortified strnlen to reuse it. */ +/* + * Defined after fortified strnlen to reuse it. However, it must still be + * possible for strlen() to be used on compile-time strings for use in + * static initializers (i.e. as a constant expression). + */ +#define strlen(p) \ + __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)), \ + __builtin_strlen(p), __fortify_strlen(p)) __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1) -__kernel_size_t strlen(const char * const p) +__kernel_size_t __fortify_strlen(const char * const p) { __kernel_size_t ret; size_t p_size = __builtin_object_size(p, 1);
In preparation for enabling Clang FORTIFY_SOURCE support, redefine strlen() as a macro that tests for being a constant expression so that strlen() can still be used in static initializers, which is lost when adding __pass_object_size and __overloadable. An example of this usage can be seen here: https://lore.kernel.org/all/202201252321.dRmWZ8wW-lkp@intel.com/ Notably, this constant expression feature of strlen() is not available for architectures that build with -ffreestanding. This means the kernel currently does not universally expect strlen() to be used this way, but since there _are_ some build configurations that depend on it, retain the characteristic for Clang FORTIFY_SOURCE builds too. Signed-off-by: Kees Cook <keescook@chromium.org> --- include/linux/fortify-string.h | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)