linux-kernel - Re: [PATCH v4 45/47] net/wan/fsl_ucc_hdlc: reject muram offsets above 64K

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Message-ID: <79101f00-e3ff-9dd0-7a05-760f8be1ff69@rasmusvillemoes.dk>
Date:   Fri, 15 Nov 2019 08:44:12 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Timur Tabi <timur@...nel.org>
Cc:     Qiang Zhao <qiang.zhao@....com>, Li Yang <leoyang.li@....com>,
        Christophe Leroy <christophe.leroy@....fr>,
        linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Scott Wood <oss@...error.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 45/47] net/wan/fsl_ucc_hdlc: reject muram offsets above
 64K

On 15/11/2019 05.41, Timur Tabi wrote:
> On Fri, Nov 8, 2019 at 7:04 AM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
> 
>> diff --git a/drivers/net/wan/fsl_ucc_hdlc.c b/drivers/net/wan/fsl_ucc_hdlc.c
>> index 8d13586bb774..f029eaa7cfc0 100644
>> --- a/drivers/net/wan/fsl_ucc_hdlc.c
>> +++ b/drivers/net/wan/fsl_ucc_hdlc.c
>> @@ -245,6 +245,11 @@ static int uhdlc_init(struct ucc_hdlc_private *priv)
>>                 ret = -ENOMEM;
>>                 goto free_riptr;
>>         }
>> +       if (riptr != (u16)riptr || tiptr != (u16)tiptr) {
> 
> "riptr/tiptr > U16_MAX" is clearer.
> 

I can change it, sure, but it's a matter of taste. To me the above asks
"does the value change when it is truncated to a u16" which makes
perfect sense when the value is next used with iowrite16be(). Using a
comparison to U16_MAX takes more brain cycles for me, because I have to
think whether it should be > or >=, and are there some
signedness/integer promotion business interfering with that test.

Rasmus