Re: [PATCH 06/14] Fix CFLAGS for UBSAN_BOUNDS on Clang

Nick Desaulniers
2020-09-14T21:17:57Z

+ kernel-dynamic-tools to help review.

On Mon, Sep 14, 2020 at 10:28 AM George-Aurelian Popescu
<georgepope@google.com> wrote:
>
> From: George Popescu <georgepope@google.com>
>
> When the kernel is compiled with Clang, UBSAN_BOUNDS inserts a brk after
> the handler call, preventing it from printing any information processed
> inside the buffer.
> For Clang -fsanitize=bounds expands to -fsanitize=array-bounds and
> -fsanitize=local-bounds, and the latter adds a brk after the handler
> call
>
> Signed-off-by: George Popescu <georgepope@google.com>
> ---
> scripts/Makefile.ubsan | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> index 27348029b2b8..3d15ac346c97 100644
> --- a/scripts/Makefile.ubsan
> +++ b/scripts/Makefile.ubsan
> @@ -4,7 +4,14 @@ ifdef CONFIG_UBSAN_ALIGNMENT
> endif
>
> ifdef CONFIG_UBSAN_BOUNDS
> - CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
> + # For Clang -fsanitize=bounds translates to -fsanitize=array-bounds and
> + # -fsanitize=local-bounds; the latter adds a brk right after the
> + # handler is called.
> + ifdef CONFIG_CC_IS_CLANG
> + CFLAGS_UBSAN += $(call cc-option, -fsanitize=array-bounds)

You can remove the cc-option check above; Clang has supported this
option for many releases. (One less compiler invocation at build
time, FWIW).

You cannot remove the below cc-option; GCC only implemented that
sanitizer in the 5.0+ releases; the kernel still support GCC 4.9.

> + else
> + CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
> + endif
> endif
>
> ifdef CONFIG_UBSAN_MISC
> --
> 2.28.0.618.gf4bc123cb7-goog
>

--
Thanks,
~Nick Desaulniers