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

[Andrii Nakryiko]

On Mon, Dec 28, 2020 at 7:49 AM Naresh Kamboju
<naresh.kamboju@xxxxxxxxxx> 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@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);
>    ^~~~~~~~
>

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?

> 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
>
> --
> Linaro LKFT
> https://lkft.linaro.org