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Date:   Mon, 10 May 2021 16:14:44 -0500
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>, pmenzel@molgen.mpg.de,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/legacy_serial: Fix UBSAN: array-index-out-of-bounds
Message-ID: <20210510211444.GE10366@gate.crashing.org>
References: <d5e3c8e66bad3725d7d48d0e45c4b7eb7c02631d.1620455671.git.christophe.leroy@csgroup.eu>
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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.


Segher