linux-kernel - Re: [PATCH] objtool: use sh_info to find the base for .rela sections

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Message-ID: <202004211307.C8E3AC87@keescook>
Date:   Tue, 21 Apr 2020 13:07:51 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] objtool: use sh_info to find the base for .rela sections

On Tue, Apr 21, 2020 at 11:25:01AM -0700, Sami Tolvanen wrote:
> ELF doesn't require .rela section names to match the base section. Use
> the section index in sh_info to find the section instead of looking it
> up by name.
> 
> LLD, for example, generates a .rela section that doesn't match the base
> section name when we merge sections in a linker script for a binary
> compiled with -ffunction-sections.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  tools/objtool/elf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
> index 09ddc8f1def3..73cfe45975c8 100644
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -468,7 +468,7 @@ static int read_relas(struct elf *elf)
>  		if (sec->sh.sh_type != SHT_RELA)
>  			continue;
>  
> -		sec->base = find_section_by_name(elf, sec->name + 5);
> +		sec->base = find_section_by_index(elf, sec->sh.sh_info);
>  		if (!sec->base) {
>  			WARN("can't find base section for rela section %s",
>  			     sec->name);
> 
> base-commit: ae83d0b416db002fe95601e7f97f64b59514d936
> -- 
> 2.26.1.301.g55bc3eb7cb9-goog
> 

-- 
Kees Cook