Re: [PATCH v3 2/8] Compiler Attributes: add __alloc_size() for better bounds checking

[Miguel Ojeda]

On Fri, Oct 1, 2021 at 12:27 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> +ifdef CONFIG_CC_IS_GCC
> +# The allocators already balk at large sizes, so silence the compiler
> +# warnings for bounds checks involving those possible values. While
> +# -Wno-alloc-size-larger-than would normally be used here, earlier versions
> +# of gcc (<9.1) weirdly don't handle the option correctly when _other_
> +# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX
> +# doesn't work (as it is documented to), silently resolving to "0" prior to
> +# version 9.1 (and producing an error more recently). Numeric values larger
> +# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently
> +# ignored, continuing to default to PTRDIFF_MAX. So, left with no other
> +# choice, we must perform a versioned check to disable this warning.
> +# https://lore.kernel.org/lkml/20210824115859.187f272f@xxxxxxxxxxxxxxxx
> +KBUILD_CFLAGS += $(call cc-ifversion, -ge, 0901, -Wno-alloc-size-larger-than)
> +endif

An amazing journey!

Reviewed-by: Miguel Ojeda <ojeda@xxxxxxxxxx>

Cheers,
Miguel