linux-kernel - Re: [PATCH 2/2] perf bpf: Check relocation target section

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Message-ID: <20160122171102.GB9608@ast-mbp.thefacebook.com>
Date:	Fri, 22 Jan 2016 09:11:03 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	ast@...nel.org, acme@...nel.org, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Li Zefan <lizefan@...wei.com>, pi3orama@....com
Subject: Re: [PATCH 2/2] perf bpf: Check relocation target section

On Fri, Jan 22, 2016 at 09:27:21AM +0000, Wang Nan wrote:
> Libbpf should check target section before doing relocation to ensure
> the relocation is correct. If not, a bug in LLVM causes error. See [1].
> Also, if an incorrect BPF script uses both global variable and
> map, global variable whould be treated as map and be relocated
> without error.
> 
> This patch saves id of map section into obj->efile and compare
> target section of a relocation symbol against it during relocation.
...
> [1] https://llvm.org/bugs/show_bug.cgi?id=26243
...
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
>  
> +		if (sym.st_shndx != maps_shndx) {
> +			pr_warning("Program '%s' contains non-map related relo data pointing to section %u\n",
> +				   prog->section_name, sym.st_shndx);
> +			return -LIBBPF_ERRNO__RELOC; 
> +		}

May be 'pr_err' instead of 'pr_warning', since such program will fail
to load by kernel anyway. Looks good otherwise.
Acked-by: Alexei Starovoitov <ast@...nel.org>