linux-kernel - Re: [PATCH] powerpc/legacy_serial: Fix UBSAN: array-index-out-of-bounds

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Message-ID: <87sg2uxe7h.fsf@mpe.ellerman.id.au>
Date:   Tue, 11 May 2021 11:16:02 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, pmenzel@...gen.mpg.de,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/legacy_serial: Fix UBSAN:
 array-index-out-of-bounds

Segher Boessenkool <segher@...nel.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.

cheers