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

George Popescu
2020-09-15T12:09:07Z

On Tue, Sep 15, 2020 at 01:18:11PM +0200, Marco Elver wrote:
> On Tue, 15 Sep 2020 at 12:25, George Popescu <georgepope@google.com> wrote:
> > On Mon, Sep 14, 2020 at 03:13:14PM -0700, Kees Cook wrote:
> > > On Mon, Sep 14, 2020 at 05:27:42PM +0000, George-Aurelian Popescu 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
> > >
> > This would mean losing the local-bounds coverage. I tried to test it without
> > local-bounds and with a locally defined array on the stack and it works fine
> > (the handler is called and the error reported). For me it feels like
> > --array-bounds and --local-bounds are triggered for the same type of
> > undefined_behaviours but they are handling them different.
>
> Does -fno-sanitize-trap=bounds help?>

I tried replacing it with:
ifdef CONFIG_CC_IS_CLANG
CFLAGS_UBSAN += $(call cc-option, -fno-sanitize-trap=bounds)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
else
CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
endif

The code traps.

Thanks,
George