linux-kernel - Re: [PATCH] cpufreq: powernv: Check negative value returned by cpufreq_table_find_index

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJZ5v0gVUO5OMfHUrQKd0T1EKo2c9iJ+zb-v9i2tkkS0MJbntA@mail.gmail.com>
Date:   Wed, 21 Feb 2018 14:25:10 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] cpufreq: powernv: Check negative value returned by cpufreq_table_find_index_dl()

On Wed, Feb 21, 2018 at 2:13 PM, Michael Ellerman <mpe@...erman.id.au> wrote:
> "Rafael J. Wysocki" <rafael@...nel.org> writes:
>
>> On Wed, Feb 21, 2018 at 6:54 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>>> On 21-02-18, 16:39, Michael Ellerman wrote:
>>>> Viresh Kumar <viresh.kumar@...aro.org> writes:
>>>
>>>> > AFAICT, you will get -1 here only if the freq table had no valid
>>>> > frequencies (or the freq table is empty). Why would that happen ?
>>>>
>>>> Bugs?
>>>
>>> The cupfreq driver shouldn't have registered itself in that case (i.e.
>>> if the cpufreq table is empty).
>>
>> To be precise, ->init() should fail as that's where the table is
>> created.  The registration fails as a result then.
>>
>> But what if the bug is that ->init() doesn't fail when it should?
>>
>> I guess the core could double check the frequency table after ->init()
>> if ->target_index is not NULL.
>>
>> The overall point here is that if you get a negative index in
>> ->fast_switch(), that's way too late anyway and we should be able to
>> catch that error much earlier.
>
> OK.
>
> Still it's one thing for the driver to print a warning and bail out,
> it's another to access off the front of an array and keep running using
> some junk values, or oops (though not in this case because the array
> happens to be static).

Well, let me rephrase.  If ->fast_switch() runs, then it must not be
possible to get a negative index in it.  That has to be guaranteed by
the core.