From: Walter Wu <walter-zh.wu@mediatek.com>
To: Marc Gonzalez <marc.w.gonzalez@free.fr>
Cc: LKML <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
Alexander Potapenko <glider@google.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Matthias Brugger <matthias.bgg@gmail.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y
Date: Tue, 1 Oct 2019 10:36:40 +0800 [thread overview]
Message-ID: <1569897400.17361.27.camel@mtksdccf07> (raw)
In-Reply-To: <a3a5e118-e6da-8d6d-5073-931653fa2808@free.fr>
On Mon, 2019-09-30 at 10:57 +0200, Marc Gonzalez wrote:
> On 30/09/2019 06:36, Walter Wu wrote:
>
> > bool check_memory_region(unsigned long addr, size_t size, bool write,
> > unsigned long ret_ip)
> > {
> > + if (long(size) < 0) {
> > + kasan_report_invalid_size(src, dest, len, _RET_IP_);
> > + return false;
> > + }
> > +
> > return check_memory_region_inline(addr, size, write, ret_ip);
> > }
>
> Is it expected that memcpy/memmove may sometimes (incorrectly) be passed
> a negative value? (It would indeed turn up as a "large" size_t)
>
> IMO, casting to long is suspicious.
>
> There seem to be some two implicit assumptions.
>
> 1) size >= ULONG_MAX/2 is invalid input
> 2) casting a size >= ULONG_MAX/2 to long yields a negative value
>
> 1) seems reasonable because we can't copy more than half of memory to
> the other half of memory. I suppose the constraint could be even tighter,
> but it's not clear where to draw the line, especially when considering
> 32b vs 64b arches.
>
> 2) is implementation-defined, and gcc works "as expected" (clang too
> probably) https://gcc.gnu.org/onlinedocs/gcc/Integers-implementation.html
>
> A comment might be warranted to explain the rationale.
> Regards.
Thanks for your suggestion.
Yes, It is passed a negative value issue in memcpy/memmove/memset.
Our current idea should be assumption 1 and only consider 64b arch,
because KASAN only supports 64b. In fact, we really can't use so much
memory in 64b arch. so assumption 1 make sense.
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next prev parent reply other threads:[~2019-10-01 2:37 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-27 3:43 [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y Walter Wu
2019-09-27 13:07 ` Dmitry Vyukov
2019-09-27 14:22 ` Walter Wu
2019-09-27 19:41 ` Dmitry Vyukov
2019-09-30 4:36 ` Walter Wu
2019-09-30 8:57 ` Marc Gonzalez
2019-10-01 2:36 ` Walter Wu [this message]
2019-10-01 3:01 ` Dmitry Vyukov
2019-10-01 3:18 ` Walter Wu
2019-10-02 12:15 ` Walter Wu
2019-10-02 13:57 ` Dmitry Vyukov
2019-10-03 2:17 ` Walter Wu
2019-10-03 6:26 ` Dmitry Vyukov
2019-10-03 9:38 ` Walter Wu
2019-10-03 13:51 ` Walter Wu
2019-10-03 14:53 ` Dmitry Vyukov
2019-10-04 4:42 ` Walter Wu
2019-10-04 8:02 ` Walter Wu
2019-10-04 9:18 ` Dmitry Vyukov
2019-10-04 9:44 ` Walter Wu
2019-10-04 9:54 ` Dmitry Vyukov
2019-10-04 12:05 ` Walter Wu
2019-10-04 13:52 ` Dmitry Vyukov
2019-10-07 3:22 ` Walter Wu
2019-10-07 7:29 ` Dmitry Vyukov
2019-10-07 8:18 ` Walter Wu
2019-10-07 8:24 ` Dmitry Vyukov
2019-10-07 8:51 ` Walter Wu
2019-10-07 8:54 ` Dmitry Vyukov
2019-10-07 9:03 ` Walter Wu
2019-10-07 9:10 ` Dmitry Vyukov
2019-10-07 9:28 ` Walter Wu
2019-10-07 9:50 ` Walter Wu
2019-10-07 10:51 ` Dmitry Vyukov
2019-10-07 12:03 ` Walter Wu
2019-10-07 12:19 ` Dmitry Vyukov
2019-10-07 12:32 ` Walter Wu
2019-10-07 13:33 ` Dmitry Vyukov
2019-10-08 6:15 ` Walter Wu
2019-10-08 9:47 ` Qian Cai
2019-10-08 11:02 ` Walter Wu
2019-10-08 11:42 ` Qian Cai
2019-10-08 12:07 ` Walter Wu
2019-10-08 12:11 ` Dmitry Vyukov
2019-10-14 2:19 ` Walter Wu
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