linux-kernel - Re: [PATCH 5.4 106/453] libbpf: Fix BTF data layout checks and allow empty BTF

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Date:   Mon, 28 Dec 2020 18:09:25 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-stable <stable@...r.kernel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH 5.4 106/453] libbpf: Fix BTF data layout checks and allow
 empty BTF

On Mon, Dec 28, 2020 at 11:47:44AM -0800, Andrii Nakryiko wrote:
>On Mon, Dec 28, 2020 at 7:49 AM Naresh Kamboju
><naresh.kamboju@...aro.org> wrote:
>>
>> Perf build failed on stable-rc 5.4 branch due to this patch.
>>
>> On Mon, 28 Dec 2020 at 19:15, Greg Kroah-Hartman
>> <gregkh@...uxfoundation.org> wrote:
>> >
>> > From: Andrii Nakryiko <andrii@...nel.org>
>> >
>> > [ Upstream commit d8123624506cd62730c9cd9c7672c698e462703d ]
>> >
>> > Make data section layout checks stricter, disallowing overlap of types and
>> > strings data.
>> >
>> > Additionally, allow BTFs with no type data. There is nothing inherently wrong
>> > with having BTF with no types (put potentially with some strings). This could
>> > be a situation with kernel module BTFs, if module doesn't introduce any new
>> > type information.
>> >
>> > Also fix invalid offset alignment check for btf->hdr->type_off.
>> >
>> > Fixes: 8a138aed4a80 ("bpf: btf: Add BTF support to libbpf")
>> > Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
>> > Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>> > Link: https://lore.kernel.org/bpf/20201105043402.2530976-8-andrii@kernel.org
>> > Signed-off-by: Sasha Levin <sashal@...nel.org>
>> > ---
>> >  tools/lib/bpf/btf.c | 16 ++++++----------
>> >  1 file changed, 6 insertions(+), 10 deletions(-)
>> >
>> > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
>> > index d606a358480da..3380aadb74655 100644
>> > --- a/tools/lib/bpf/btf.c
>> > +++ b/tools/lib/bpf/btf.c
>> > @@ -100,22 +100,18 @@ static int btf_parse_hdr(struct btf *btf)
>> >                 return -EINVAL;
>> >         }
>> >
>> > -       if (meta_left < hdr->type_off) {
>> > -               pr_debug("Invalid BTF type section offset:%u\n", hdr->type_off);
>> > +       if (meta_left < hdr->str_off + hdr->str_len) {
>> > +               pr_debug("Invalid BTF total size:%u\n", btf->raw_size);
>>
>> In file included from btf.c:17:0:
>> btf.c: In function 'btf_parse_hdr':
>> btf.c:104:48: error: 'struct btf' has no member named 'raw_size'; did
>> you mean 'data_size'?
>>    pr_debug("Invalid BTF total size:%u\n", btf->raw_size);
>>                                                 ^
>> libbpf_internal.h:59:40: note: in definition of macro '__pr'
>>   libbpf_print(level, "libbpf: " fmt, ##__VA_ARGS__); \
>>                                         ^~~~~~~~~~~
>> btf.c:104:3: note: in expansion of macro 'pr_debug'
>>    pr_debug("Invalid BTF total size:%u\n", btf->raw_size);
>>    ^~~~~~~~
>>
>
>This patch fixes the bug introduced back in 8a138aed4a80 ("bpf: btf:
>Add BTF support to libbpf"), but a bunch of other refactorings
>happened since then, adding/renaming struct btf internals. The fix
>here is not that critical, so it's probably best to just drop this
>patch from the stable, if possible. Would it be ok, Greg?

I'll drop it, thanks.

-- 
Thanks,
Sasha