netdev - Re: [PATCH iproute2 -master] tc, bpf: make sure relo is in relation with map section

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Message-ID: <20160122031343.GA6593@ast-mbp.thefacebook.com>
Date:	Thu, 21 Jan 2016 19:13:44 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	stephen@...workplumber.org, netdev@...r.kernel.org,
	wangnan0@...wei.com
Subject: Re: [PATCH iproute2 -master] tc, bpf: make sure relo is in relation
 with map section

On Fri, Jan 22, 2016 at 12:46:28AM +0100, Daniel Borkmann wrote:
> Add a test that symbol from relocation entry is actually related
> to map section and bail out with an error message if it's not the
> case; in relation to [1].
> 
>   [1] https://llvm.org/bugs/show_bug.cgi?id=26243
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

Acked-by: Alexei Starovoitov <ast@...nel.org>

Thanks. Useful check.
Wang, we probably want something like this in libbpf as well.

> ---
>  tc/tc_bpf.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tc/tc_bpf.c b/tc/tc_bpf.c
> index 219ffa5..3c97cdb 100644
> --- a/tc/tc_bpf.c
> +++ b/tc/tc_bpf.c
> @@ -1336,6 +1336,12 @@ static int bpf_apply_relo_data(struct bpf_elf_ctx *ctx,
>  
>  		if (gelf_getsym(ctx->sym_tab, GELF_R_SYM(relo.r_info), &sym) != &sym)
>  			return -EIO;
> +		if (sym.st_shndx != ctx->sec_maps) {
> +			fprintf(stderr, "ELF contains non-map related relo data in "
> +				"entry %u pointing to section %u! Compiler bug?!\n",
> +				relo_ent, sym.st_shndx);
> +			return -EIO;
> +		}
>  
>  		rmap = sym.st_value / sizeof(struct bpf_elf_map);
>  		if (rmap >= ARRAY_SIZE(ctx->map_fds))
> -- 
> 1.9.3
>