Instead of defining memcpy() in terms of __builtin_memcpy() deep in arch/x86/include/asm/string_32.h, notice that it is needed up in the general string.h, as done with other common C String APIs. This allows us to add basic sanity checking for pathological "size" arguments to memcpy(). Besides the run-time checking benefit, this avoids GCC trying to be very smart about value range tracking[1] when CONFIG_PROFILE_ALL_BRANCHES=y but FORTIFY_SOURCE=n.
Link: https://lore.kernel.org/all/202505191117.C094A90F88@keescook/ [1] Reported-by: kernel test robot <[email protected]> Closes: https://lore.kernel.org/all/[email protected]/ Reported-by: Randy Dunlap <[email protected]> Closes: https://lore.kernel.org/all/[email protected]/ Signed-off-by: Kees Cook <[email protected]> --- Cc: "Mickaël Salaün" <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Dave Hansen <[email protected]> Cc: <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Andy Shevchenko <[email protected]> Cc: Uros Bizjak <[email protected]> Cc: <[email protected]> --- arch/x86/include/asm/string_32.h | 6 ------ include/linux/string.h | 13 +++++++++++++ 2 files changed, 13 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/string_32.h b/arch/x86/include/asm/string_32.h index 32c0d981a82a..fad9566f43a6 100644 --- a/arch/x86/include/asm/string_32.h +++ b/arch/x86/include/asm/string_32.h @@ -145,12 +145,6 @@ static __always_inline void *__constant_memcpy(void *to, const void *from, #define __HAVE_ARCH_MEMCPY extern void *memcpy(void *, const void *, size_t); -#ifndef CONFIG_FORTIFY_SOURCE - -#define memcpy(t, f, n) __builtin_memcpy(t, f, n) - -#endif /* !CONFIG_FORTIFY_SOURCE */ - #define __HAVE_ARCH_MEMMOVE void *memmove(void *dest, const void *src, size_t n); diff --git a/include/linux/string.h b/include/linux/string.h index 01621ad0f598..a1f8fdcf8482 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -4,6 +4,7 @@ #include <linux/args.h> #include <linux/array_size.h> +#include <linux/bug.h> #include <linux/cleanup.h> /* for DEFINE_FREE() */ #include <linux/compiler.h> /* for inline */ #include <linux/types.h> /* for size_t */ @@ -390,7 +391,19 @@ static inline const char *kbasename(const char *path) #if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE) #include <linux/fortify-string.h> +#else +/* Basic sanity checking even without FORTIFY_SOURCE */ +# ifndef __HAVE_ARCH_MEMCPY +# define memcpy(t, f, n) \ + do { \ + typeof(n) __n = (n); \ + /* Skip impossible sizes. */ \ + if (!WARN_ON(__n < 0 || __n == SIZE_MAX)) \ + __builtin_memcpy(t, f, __n); \ + } while (0) +# endif #endif + #ifndef unsafe_memcpy #define unsafe_memcpy(dst, src, bytes, justification) \ memcpy(dst, src, bytes) -- 2.34.1
