Re: [PATCH v3 12/15] kasan: fix bug detection via ksize for HW_TAGS mode

[Alexander Potapenko]

On Fri, Jan 15, 2021 at 2:18 PM Marco Elver <elver@xxxxxxxxxx> wrote:
>
> On Thu, Jan 14, 2021 at 08:36PM +0100, Andrey Konovalov wrote:
> > The currently existing kasan_check_read/write() annotations are intended
> > to be used for kernel modules that have KASAN compiler instrumentation
> > disabled. Thus, they are only relevant for the software KASAN modes that
> > rely on compiler instrumentation.
> >
> > However there's another use case for these annotations: ksize() checks
> > that the object passed to it is indeed accessible before unpoisoning the
> > whole object. This is currently done via __kasan_check_read(), which is
> > compiled away for the hardware tag-based mode that doesn't rely on
> > compiler instrumentation. This leads to KASAN missing detecting some
> > memory corruptions.
> >
> > Provide another annotation called kasan_check_byte() that is available
> > for all KASAN modes. As the implementation rename and reuse
> > kasan_check_invalid_free(). Use this new annotation in ksize().
> > To avoid having ksize() as the top frame in the reported stack trace
> > pass _RET_IP_ to __kasan_check_byte().
> >
> > Also add a new ksize_uaf() test that checks that a use-after-free is
> > detected via ksize() itself, and via plain accesses that happen later.
> >
> > Link: https://linux-review.googlesource.com/id/Iaabf771881d0f9ce1b969f2a62938e99d3308ec5
> > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>
> Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>