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Date: Tue, 19 May 2020 11:00:31 -0400 From: Qian Cai <cai@....pw> To: Andrii Nakryiko <andrii.nakryiko@...il.com> Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, Andrii Nakryiko <andriin@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...omium.org>, Linux Netdev List <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, clang-built-linux <clang-built-linux@...glegroups.com>, Kees Cook <keescook@...omium.org> Subject: Re: UBSAN: array-index-out-of-bounds in kernel/bpf/arraymap.c:177 On Mon, May 18, 2020 at 8:25 PM Andrii Nakryiko <andrii.nakryiko@...il.com> wrote: > > On Mon, May 18, 2020 at 5:09 PM Qian Cai <cai@....pw> wrote: > > > > On Mon, May 18, 2020 at 7:55 PM Andrii Nakryiko > > <andrii.nakryiko@...il.com> wrote: > > > > > > On Sun, May 17, 2020 at 7:45 PM Qian Cai <cai@....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; }
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