linux-kernel - Re: arm64: pstore: printk causing hang during boot in __memcpy

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: <CABXF_ACKZXe+3J76bfyr4V1qdyhJ--cTekSXSVPksKOTxCBfTQ@mail.gmail.com>
Date:   Wed, 1 Aug 2018 22:46:06 +0530
From:   Ivid Suvarna <ivid.suvarna@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jason Baron <jbaron@...hat.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        Joe Perches <joe@...ches.com>, linux-arm-msm@...r.kernel.org
Subject: Re: arm64: pstore: printk causing hang during boot in __memcpy_toio
 with pstore enabled

On Wed, Aug 1, 2018 at 6:49 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> On 08/01/2018 05:35 AM, Ivid Suvarna wrote:
>>
>> Hi,
>>
>> When pstore is enabled and a *pr_info(any printk) in
>> __memcpy_toio(arch/arm64/kernel/io.c)* is added, kernel wont boot and
>> just hangs.
>>
>> The path where __memcpy_toio is called is below:
>>
>> ->persistent_ram_update
>>    -> memcpy_toio
>>      -> __memcpy_toio
>>
>> I tried with trace_printk and kernel boots fine. I understand that
>> printk has overhead, but is this expected when we use some printk
>> statement in __memcpy_toio?
>>
>
> I think the problem may be that the printk() output is copied to pstore.
> Since pstore calls memcpy_toio(), you get a nice recursion if you add a
> printk() call to it.
>

Is there any solution to this other than not adding printk :p