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

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Date:   Fri, 2 Sep 2022 10:42:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Sathvika Vasireddy <sv@...ux.ibm.com>,
        "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

On Fri, Sep 02, 2022 at 08:06:28AM +0000, Christophe Leroy wrote:
> 
> 
> 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.

Fair enough.

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>