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| author | Kees Cook <keescook@chromium.org> | 2022-02-08 23:53:49 +0100 |
|---|---|---|
| committer | Kees Cook <keescook@chromium.org> | 2022-02-14 01:50:07 +0100 |
| commit | 67ebc3ab446230c77fe3b545a9d8a11cac1cfb6e (patch) | |
| tree | 712643fdda5c0f50442eb4d9238daaa2035be71f | |
| parent | fortify: Use __diagnose_as() for better diagnostic coverage (diff) | |
| download | linux-67ebc3ab446230c77fe3b545a9d8a11cac1cfb6e.tar.xz linux-67ebc3ab446230c77fe3b545a9d8a11cac1cfb6e.zip | |
fortify: Make sure strlen() may still be used as a constant expression
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>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20220208225350.1331628-8-keescook@chromium.org
| -rw-r--r-- | include/linux/fortify-string.h | 13 |
1 files 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)), \ + __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); |