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

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Message-ID: <56A582A2.1050703@huawei.com>
Date:	Mon, 25 Jan 2016 10:04:18 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.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 2016/1/25 9:56, Wangnan (F) wrote:
>
>
> On 2016/1/23 1:11, Alexei Starovoitov wrote:
>> 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;

There's a trailing whitespace. Sorry.

>>> +        }
>> May be 'pr_err' instead of 'pr_warning', since such program will fail
>> to load by kernel anyway.
>
> Libbpf doesn't issue pr_error even in fatal exception because it 
> doesn't define
> pr_err at all. It reports error code and let perf deal with error.
>
> Thank you.
>
>>   Looks good otherwise.
>> Acked-by: Alexei Starovoitov <ast@...nel.org>
>>
>