Re: [PATCH v3] x86/boot: Warn on future overlapping memcpy() use

[Kees Cook]

(Sorry, this v3 got sent to an incomplete CC list...)


On Thu, Apr 28, 2016 at 4:46 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> If an overlapping memcpy() is ever attempted, we should report it and
> gracefully call memmove(). These cases can be found and fixed to use
> memmove() correctly, but in the meantime, we will not break booting.
>
> Suggested-by: Ingo Molnar <mingo@xxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/string.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
> index 2befeca1aada..7402227fdfdb 100644
> --- a/arch/x86/boot/compressed/string.c
> +++ b/arch/x86/boot/compressed/string.c
> @@ -8,7 +8,7 @@
>  #include "../string.c"
>
>  #ifdef CONFIG_X86_32
> -void *memcpy(void *dest, const void *src, size_t n)
> +static void *__memcpy(void *dest, const void *src, size_t n)
>  {
>         int d0, d1, d2;
>         asm volatile(
> @@ -22,7 +22,7 @@ void *memcpy(void *dest, const void *src, size_t n)
>         return dest;
>  }
>  #else
> -void *memcpy(void *dest, const void *src, size_t n)
> +static void *__memcpy(void *dest, const void *src, size_t n)
>  {
>         long d0, d1, d2;
>         asm volatile(
> @@ -60,3 +60,14 @@ void *memmove(void *dest, const void *src, size_t n)
>
>         return dest;
>  }
> +
> +/* Detect and warn about potential overlaps, but handle them with memmove. */
> +void *memcpy(void *dest, const void *src, size_t n)
> +{
> +       if (dest > src && dest - src < n) {
> +               warn("Avoiding potentially unsafe overlapping memcpy()!");
> +               return memmove(dest, src, n);
> +       }
> +       return __memcpy(dest, src, n);
> +}
> +
> --
> 2.6.3
>
>
> --
> Kees Cook
> Chrome OS & Brillo Security



-- 
Kees Cook
Chrome OS & Brillo Security