From: Kees Cook <keescook@chromium.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: masahiroy@kernel.org, nicolas@fjasle.eu, ndesaulniers@google.com,
morbo@google.com, justinstitt@google.com, maskray@google.com,
linux-kbuild@vger.kernel.org, bpf@vger.kernel.org,
llvm@lists.linux.dev, patches@lists.linux.dev,
stable@vger.kernel.org
Subject: Re: [PATCH] kbuild: Fix changing ELF file type for output of gen_btf for big endian
Date: Fri, 9 Feb 2024 16:48:59 -0800 [thread overview]
Message-ID: <202402091648.2B8D95062B@keescook> (raw)
In-Reply-To: <20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-v1-1-cb3112491edc@kernel.org>
On Thu, Feb 08, 2024 at 01:21:06PM -0700, Nathan Chancellor wrote:
> Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> changed the ELF type of .btf.vmlinux.bin.o from ET_EXEC to ET_REL via
> dd, which works fine for little endian platforms:
>
> 00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> +00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
>
> However, for big endian platforms, it changes the wrong byte, resulting
> in an invalid ELF file type, which ld.lld rejects:
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: <unknown>: 103
>
> ld.lld: error: .btf.vmlinux.bin.o: unknown file type
>
> Fix this by using a different seek value for dd when targeting big
> endian, so that the correct byte gets changed and everything works
> correctly for all linkers.
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: REL (Relocatable file)
>
> Cc: stable@vger.kernel.org
> Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> Link: https://github.com/llvm/llvm-project/pull/75643
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Yeah, looks good to me.
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
next prev parent reply other threads:[~2024-02-10 0:49 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-08 20:21 [PATCH] kbuild: Fix changing ELF file type for output of gen_btf for big endian Nathan Chancellor
2024-02-08 21:10 ` Nicolas Schier
2024-02-08 21:22 ` Fangrui Song
2024-02-08 21:50 ` Justin Stitt
2024-02-10 0:48 ` Kees Cook [this message]
2024-02-13 0:55 ` Masahiro Yamada
2024-02-13 1:43 ` Nathan Chancellor
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