linux-kernel - Re: [PATCH v2 03/15] NTB: Fix UB/bug in ntb_mw_get

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Date:   Tue, 5 Dec 2017 10:01:22 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Jon Mason <jdmason@...zu.us>, Serge Semin <fancer.lancer@...il.com>
Cc:     Dave Jiang <dave.jiang@...el.com>,
        "Hubbe, Allen" <Allen.Hubbe@....com>,
        "S-k, Shyam-sundar" <Shyam-sundar.S-k@....com>,
        "Yu, Xiangliang" <Xiangliang.Yu@....com>,
        Gary R Hook <gary.hook@....com>, Sergey.Semin@...latforms.ru,
        linux-ntb <linux-ntb@...glegroups.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 03/15] NTB: Fix UB/bug in ntb_mw_get_align()



On 05/12/17 09:52 AM, Jon Mason wrote:
> On Sun, Dec 3, 2017 at 2:17 PM, Serge Semin <fancer.lancer@...il.com> wrote:
>> Simple (1 << pidx) operation causes undefined behaviour when
>> pidx >= 32. It must be casted to u64 to match the actual return
>> value of ntb_link_is_up() method, so to have all the possible
>> peer indexes covered and to get rid of undefined behaviour.
>> Additionally there are special macros in "linux/bitops.h" to perform
>> the bit-set-shift operations, so it's recommended to have them used
>> for proper bit setting.
> 
> This looks good to me, but also seems like a bug fix.  Please comment
> on if this is not noticed.

It would be a bug on any system that has more than 32 partitions which 
is run on a 32 bit machine (or 64 partitions on a 64bit machine). Such a 
system is theoretical for the foreseeable future. But it would be good 
to fix it now.

Logan