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

[Naresh Kamboju]

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@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Andrii Nakryiko <andrii@xxxxxxxxxx>
>
> [ 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@xxxxxxxxxx>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> Link: https://lore.kernel.org/bpf/20201105043402.2530976-8-andrii@xxxxxxxxxx
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  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);
   ^~~~~~~~

full build log link,
https://ci.linaro.org/view/lkft/job/openembedded-lkft-linux-stable-rc-5.4/DISTRO=lkft,MACHINE=intel-corei7-64,label=docker-buster-lkft/346/consoleText

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