From: Qian Cai <cai@lca.pw>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
Linux Netdev List <netdev@vger.kernel.org>,
bpf <bpf@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Kees Cook <keescook@chromium.org>
Subject: Re: UBSAN: array-index-out-of-bounds in kernel/bpf/arraymap.c:177
Date: Tue, 19 May 2020 11:00:31 -0400 [thread overview]
Message-ID: <CAG=TAF5rYmMXBcxno0pPxVZdcyz=ik-enh03E-V8wupjDS0K5g@mail.gmail.com> (raw)
In-Reply-To: <CAEf4BzaBfnDL=WpRP-7rYFhocOsCQyFuZaLvM0+k9sv2t_=rVw@mail.gmail.com>
On Mon, May 18, 2020 at 8:25 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Mon, May 18, 2020 at 5:09 PM Qian Cai <cai@lca.pw> wrote:
> >
> > On Mon, May 18, 2020 at 7:55 PM Andrii Nakryiko
> > <andrii.nakryiko@gmail.com> wrote:
> > >
> > > On Sun, May 17, 2020 at 7:45 PM Qian Cai <cai@lca.pw> wrote:
> > > >
> > > > With Clang 9.0.1,
> > > >
> > > > return array->value + array->elem_size * (index & array->index_mask);
> > > >
> > > > but array->value is,
> > > >
> > > > char value[0] __aligned(8);
> > >
> > > This, and ptrs and pptrs, should be flexible arrays. But they are in a
> > > union, and unions don't support flexible arrays. Putting each of them
> > > into anonymous struct field also doesn't work:
> > >
> > > /data/users/andriin/linux/include/linux/bpf.h:820:18: error: flexible
> > > array member in a struct with no named members
> > > struct { void *ptrs[] __aligned(8); };
> > >
> > > So it probably has to stay this way. Is there a way to silence UBSAN
> > > for this particular case?
> >
> > I am not aware of any way to disable a particular function in UBSAN
> > except for the whole file in kernel/bpf/Makefile,
> >
> > UBSAN_SANITIZE_arraymap.o := n
> >
> > If there is no better way to do it, I'll send a patch for it.
>
>
> That's probably going to be too drastic, we still would want to
> validate the rest of arraymap.c code, probably. Not sure, maybe
> someone else has better ideas.
This works although it might makes sense to create a pair of
ubsan_disable_current()/ubsan_enable_current() for it.
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 11584618e861..6415b089725e 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -170,11 +170,16 @@ static void *array_map_lookup_elem(struct
bpf_map *map, void *key)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
u32 index = *(u32 *)key;
+ void *elem;
if (unlikely(index >= array->map.max_entries))
return NULL;
- return array->value + array->elem_size * (index & array->index_mask);
+ current->in_ubsan++;
+ elem = array->value + array->elem_size * (index & array->index_mask);
+ current->in_ubsan--;
+
+ return elem;
}
next prev parent reply other threads:[~2020-05-19 15:00 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-18 2:44 UBSAN: array-index-out-of-bounds in kernel/bpf/arraymap.c:177 Qian Cai
2020-05-18 23:55 ` Andrii Nakryiko
2020-05-19 0:09 ` Qian Cai
2020-05-19 0:25 ` Andrii Nakryiko
2020-05-19 1:00 ` Yonghong Song
2020-05-19 1:30 ` Andrii Nakryiko
2020-05-19 1:36 ` Yonghong Song
2020-05-19 15:00 ` Qian Cai [this message]
2020-05-19 19:29 ` Andrii Nakryiko
2020-05-19 20:18 ` Qian Cai
2020-05-19 23:23 ` Andrii Nakryiko
2020-05-20 1:55 ` Qian Cai
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