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Subject: Re: [PATCH] powerpc/legacy_serial: Fix UBSAN:
 array-index-out-of-bounds
To:     Michael Ellerman <mpe@ellerman.id.au>,
        Segher Boessenkool <segher@kernel.crashing.org>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, pmenzel@molgen.mpg.de,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
References: <d5e3c8e66bad3725d7d48d0e45c4b7eb7c02631d.1620455671.git.christophe.leroy@csgroup.eu>
 <20210510211444.GE10366@gate.crashing.org>
 <87sg2uxe7h.fsf@mpe.ellerman.id.au>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <c3d6c5c5-0eb8-bad5-91f9-fea01eaeef37@csgroup.eu>
Date:   Tue, 11 May 2021 06:54:14 +0200
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Le 11/05/2021 à 03:16, Michael Ellerman a écrit :
> Segher Boessenkool <segher@kernel.crashing.org> writes:
> 
>> On Sat, May 08, 2021 at 06:36:21AM +0000, Christophe Leroy wrote:
>>> UBSAN complains when a pointer is calculated with invalid
>>> 'legacy_serial_console' index, allthough the index is verified
>>> before dereferencing the pointer.
>>
>> Addressing like this is UB already.
>>
>> You could just move this:
>>
>>> -	if (legacy_serial_console < 0)
>>> -		return 0;
>>
>> to before
>>
>>> -	struct legacy_serial_info *info = &legacy_serial_infos[legacy_serial_console];
>>> -	struct plat_serial8250_port *port = &legacy_serial_ports[legacy_serial_console];
>>
>> and no other change is necessary.
> 
> Yeah I sent a v2 doing that, thanks.
> 

I wanted something looking similar to setup_legacy_serial_console(), but of course this also works.

Christophe