netdev - Re: [PATCH v2 bpf 0/2] Fix BTF verification of enum members with a selftest

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Date:   Tue, 10 Mar 2020 09:46:27 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Yoshiki Komachi <komachi.yoshiki@...il.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
Subject: Re: [PATCH v2 bpf 0/2] Fix BTF verification of enum members with a
 selftest

On Tue, Mar 10, 2020 at 04:32:28PM +0900, Yoshiki Komachi wrote:
> btf_enum_check_member() checked if the size of "enum" as a struct
> member exceeded struct_size or not. Then, the function compared it
> with the size of "int". Although the size of "enum" is 4-byte by
> default (i.e., equivalent to "int"), the packing feature enables
> us to reduce it, as illustrated by the following example:
> 
> struct A {
>         char m;
>         enum { E0, E1 } __attribute__((packed)) n;
> };
> 
> With such a setup above, the bpf loader gave an error attempting
> to load it:
> 
> ------------------------------------------------------------------
> ...
> 
> [3] ENUM (anon) size=1 vlen=2
>         E0 val=0
>         E1 val=1
> [4] STRUCT A size=2 vlen=2
>         m type_id=2 bits_offset=0
>         n type_id=3 bits_offset=8
> 
> [4] STRUCT A size=2 vlen=2
>         n type_id=3 bits_offset=8 Member exceeds struct_size
> 
> libbpf: Error loading .BTF into kernel: -22.
> 
> ------------------------------------------------------------------
> 
> The related issue was previously fixed by the commit 9eea98497951 ("bpf:
> fix BTF verification of enums"). On the other hand, this series fixes
> this issue as well, and adds a selftest program for it.
> 
> Changes in v2:
> - change an example in commit message based on Andrii's review
> - add a selftest program for packed "enum" type members in struct/union
Acked-by: Martin KaFai Lau <kafai@...com>