linux-kernel - Re: [PATCH v2 08/16] objtool: Fix SEGFAULT

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Date:   Fri, 2 Sep 2022 08:06:28 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Peter Zijlstra <peterz@...radead.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aik@...abs.ru" <aik@...abs.ru>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "chenzhongjin@...wei.com" <chenzhongjin@...wei.com>,
        "naveen.n.rao@...ux.vnet.ibm.com" <naveen.n.rao@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 08/16] objtool: Fix SEGFAULT



Le 01/09/2022 à 21:20, Peter Zijlstra a écrit :
> On Mon, Aug 29, 2022 at 11:22:15AM +0530, Sathvika Vasireddy wrote:
>> From: Christophe Leroy <christophe.leroy@...roup.eu>
>>
>> find_insn() will return NULL in case of failure. Check insn in order
>> to avoid a kernel Oops for NULL pointer dereference.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   tools/objtool/check.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
>> index 91678252a9b6..ed2fdfeb1d9c 100644
>> --- a/tools/objtool/check.c
>> +++ b/tools/objtool/check.c
>> @@ -205,7 +205,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
>>   		return false;
>>   
>>   	insn = find_insn(file, func->sec, func->offset);
>> -	if (!insn->func)
>> +	if (!insn || !insn->func)
>>   		return false;
> 
> I suppose this is ok, but how can the lookup for func->sec, func->offset
> *not* find an instruction ?!

That happened to me at the begining when the port to powerpc was not 
fully functionnal.

I guess that could also happen with a corrupted object file so better 
safe than sorry.