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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v2 bpf-next 07/17] libbpf: factor out symtab and relos sanity checks
Date: Thu, 22 Apr 2021 11:16:48 -0700	[thread overview]
Message-ID: <CAEf4BzZWA+sPoHYBNK6+3yWcAUBd4KJuiUGOsMbbs0wSBvjcKw@mail.gmail.com> (raw)
In-Reply-To: <6fb105a3-ffc3-1970-8833-429e5b624e31@fb.com>

On Thu, Apr 22, 2021 at 9:06 AM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 4/16/21 1:23 PM, Andrii Nakryiko wrote:
> > Factor out logic for sanity checking SHT_SYMTAB and SHT_REL sections into
> > separate sections. They are already quite extensive and are suffering from too
> > deep indentation. Subsequent changes will extend SYMTAB sanity checking
> > further, so it's better to factor each into a separate function.
> >
> > No functional changes are intended.
> >
> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
>
> Ack with a minor suggestion below.
> Acked-by: Yonghong Song <yhs@fb.com>
>
> > ---
> >   tools/lib/bpf/linker.c | 233 ++++++++++++++++++++++-------------------
> >   1 file changed, 127 insertions(+), 106 deletions(-)
> >

[...]

> >
> > -                     /* .rel<secname> -> <secname> pattern is followed */
> > -                     if (strncmp(sec->sec_name, ".rel", sizeof(".rel") - 1) != 0
> > -                         || strcmp(sec->sec_name + sizeof(".rel") - 1, link_sec->sec_name) != 0) {
> > -                             pr_warn("ELF relo section #%zu name has invalid name in %s\n",
> > -                                     sec->sec_idx, obj->filename);
> > +     n = sec->shdr->sh_size / sec->shdr->sh_entsize;
> > +     sym = sec->data->d_buf;
> > +     for (i = 0; i < n; i++, sym++) {
> > +             if (sym->st_shndx
> > +                 && sym->st_shndx < SHN_LORESERVE
> > +                 && sym->st_shndx >= obj->sec_cnt) {
> > +                     pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
> > +                             i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
> > +                     return -EINVAL;
> > +             }
> > +             if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) {
> > +                     if (sym->st_value != 0)
> >                               return -EINVAL;
> > -                     }
> > +                     continue;
>
> I think this "continue" is not necessary.
>

yes, but I wanted to make it clear that there should be no more logic
handling STT_SECTION afterwards, if/when we extend the logic of this
loop. We have similar patterns with goto to keep logic more modular
and easily extensible:


    if (something) {
        err = -EINVAL;
        goto err_out;
    }


err_out:
    return err;


So let's keep it as is.

> > +             }
> > +     }
> >
> > -                     /* don't further validate relocations for ignored sections */
> > -                     if (link_sec->skipped)
> > -                             break;
> > +     return 0;
> > +}
> >
> > -                     /* relocatable section is data or instructions */
> > -                     if (link_sec->shdr->sh_type != SHT_PROGBITS
> > -                         && link_sec->shdr->sh_type != SHT_NOBITS) {
> > -                             pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n",
> > -                                     sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
> > -                             return -EINVAL;
> > -                     }
> [...]

  reply	other threads:[~2021-04-22 18:17 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 20:23 [PATCH v2 bpf-next 00/17] BPF static linker: support externs Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 01/17] bpftool: support dumping BTF VAR's "extern" linkage Andrii Nakryiko
2021-04-22  3:02   ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 02/17] bpftool: dump more info about DATASEC members Andrii Nakryiko
2021-04-22  3:09   ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 03/17] libbpf: suppress compiler warning when using SEC() macro with externs Andrii Nakryiko
2021-04-22  3:47   ` Yonghong Song
2021-04-22  3:59     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 04/17] libbpf: mark BPF subprogs with hidden visibility as static for BPF verifier Andrii Nakryiko
2021-04-22  5:43   ` Yonghong Song
2021-04-22 18:09     ` Andrii Nakryiko
2021-04-22 23:00       ` Yonghong Song
2021-04-22 23:28         ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 05/17] libbpf: allow gaps in BPF program sections to support overriden weak functions Andrii Nakryiko
2021-04-22  6:25   ` Yonghong Song
2021-04-22 18:10     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 06/17] libbpf: refactor BTF map definition parsing Andrii Nakryiko
2021-04-22 15:33   ` Yonghong Song
2021-04-22 18:40     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 07/17] libbpf: factor out symtab and relos sanity checks Andrii Nakryiko
2021-04-22 16:06   ` Yonghong Song
2021-04-22 18:16     ` Andrii Nakryiko [this message]
2021-04-16 20:23 ` [PATCH v2 bpf-next 08/17] libbpf: make few internal helpers available outside of libbpf.c Andrii Nakryiko
2021-04-22 16:19   ` Yonghong Song
2021-04-22 18:18     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 09/17] libbpf: extend sanity checking ELF symbols with externs validation Andrii Nakryiko
2021-04-22 16:35   ` Yonghong Song
2021-04-22 18:20     ` Andrii Nakryiko
2021-04-22 23:13       ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking Andrii Nakryiko
2021-04-22 16:50   ` Yonghong Song
2021-04-22 18:24     ` Andrii Nakryiko
2021-04-23  2:54       ` Alexei Starovoitov
2021-04-23  4:25         ` Andrii Nakryiko
2021-04-23  5:11           ` Alexei Starovoitov
2021-04-23 16:09             ` Andrii Nakryiko
2021-04-23 16:18               ` Alexei Starovoitov
2021-04-23 16:30                 ` Andrii Nakryiko
2021-04-23 16:34                   ` Alexei Starovoitov
2021-04-23 17:02                     ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 11/17] libbpf: add linker extern resolution support for functions and global variables Andrii Nakryiko
2021-04-22 21:27   ` Yonghong Song
2021-04-22 22:12     ` Andrii Nakryiko
2021-04-22 23:57       ` Yonghong Song
2021-04-23  2:36         ` Yonghong Song
2021-04-23  4:28           ` Andrii Nakryiko
2021-04-23  4:27         ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section Andrii Nakryiko
2021-04-22 22:56   ` Yonghong Song
2021-04-22 23:32     ` Andrii Nakryiko
2021-04-16 20:24 ` [PATCH v2 bpf-next 13/17] selftests/bpf: use -O0 instead of -Og in selftests builds Andrii Nakryiko
2021-04-23  0:05   ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 14/17] selftests/bpf: omit skeleton generation for multi-linked BPF object files Andrii Nakryiko
2021-04-23  0:13   ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 15/17] selftests/bpf: add function linking selftest Andrii Nakryiko
2021-04-23  0:50   ` Yonghong Song
2021-04-23  2:34     ` Alexei Starovoitov
2021-04-23  4:29       ` Andrii Nakryiko
2021-04-23 17:18     ` Andrii Nakryiko
2021-04-23 17:35       ` Yonghong Song
2021-04-23 17:55         ` Andrii Nakryiko
2021-04-23 17:58           ` Yonghong Song
2021-04-23 17:59             ` Andrii Nakryiko
2021-04-16 20:24 ` [PATCH v2 bpf-next 16/17] selftests/bpf: add global variables " Andrii Nakryiko
2021-04-23  1:01   ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 17/17] sleftests/bpf: add map " Andrii Nakryiko
2021-04-23  1:20   ` Yonghong Song

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