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

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Date:   Thu, 1 Sep 2022 21:20:47 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sathvika Vasireddy <sv@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, jpoimboe@...hat.com,
        linux-kernel@...r.kernel.org, aik@...abs.ru, mpe@...erman.id.au,
        mingo@...hat.com, christophe.leroy@...roup.eu, rostedt@...dmis.org,
        mbenes@...e.cz, npiggin@...il.com, chenzhongjin@...wei.com,
        naveen.n.rao@...ux.vnet.ibm.com
Subject: Re: [PATCH v2 08/16] objtool: Fix SEGFAULT

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 ?!