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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 8 Oct 2019 14:11:23 +0200
Message-ID: <CACT4Y+Zbx-2yR-mN5GioaKUgGH1TpTE2D-OgLbR2Dy09ezyGGQ@mail.gmail.com>
Subject: Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy
 with CONFIG_KASAN_GENERIC=y
To:     Qian Cai <cai@lca.pw>
Cc:     Walter Wu <walter-zh.wu@mediatek.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux-MM <linux-mm@kvack.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-mediatek@lists.infradead.org,
        wsd_upstream <wsd_upstream@mediatek.com>
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On Tue, Oct 8, 2019 at 1:42 PM Qian Cai <cai@lca.pw> wrote:
> > On Oct 8, 2019, at 7:02 AM, Walter Wu <walter-zh.wu@mediatek.com> wrote:
> > I don't know very well in UBSAN, but I try to build ubsan kernel and
> > test a negative number in memset and kmalloc_memmove_invalid_size(), it
> > look like no check.
>
> It sounds like more important to figure out why the UBSAN is not working in this case rather than duplicating functionality elsewhere.

Detecting out-of-bounds accesses is the direct KASAN responsibility.
Even more direct than for KUBSAN. We are not even adding
functionality, it's just a plain bug in KASAN code, it tricks itself
into thinking that access size is 0.
Maybe it's already detected by KUBSAN too?