Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Mime-Version: 1.0
Subject: RE: [RFC] vsprintf: compile error on %09pK
Reply-To: jaewon31.kim@samsung.com
Sender: Jaewon Kim <jaewon31.kim@samsung.com>
From:   Jaewon Kim <jaewon31.kim@samsung.com>
To:     Petr Mladek <pmladek@suse.com>,
        Jaewon Kim <jaewon31.kim@samsung.com>
CC:     David Laight <David.Laight@aculab.com>,
        'Jaewon Kim' <jaewon31.kim@gmail.com>,
        "senozhatsky@chromium.org" <senozhatsky@chromium.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        GyeongHwan Hong <gh21.hong@samsung.com>
In-Reply-To: <ZCwSIy5Tm0jAe1Ww@alley>
Message-ID: <20230404123345epcms1p1518b92632293f3f0bd7d12a29ba7c3e2@epcms1p1>
Date:   Tue, 04 Apr 2023 21:33:45 +0900
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="utf-8"
CMS-TYPE: 101P
DLP-Filter: Pass
References: <ZCwSIy5Tm0jAe1Ww@alley>
        <694722c9409b43808cfbc1fc9e495016@AcuMS.aculab.com>
        <20230403104617epcms1p383bacbca705c0d7e4fffca6833050e42@epcms1p3>
        <ZCrMMQt2xnnZIyz6@alley>
        <CAJrd-Uvzy18SfjjqbqZCPHjw+ujQXsBpvov4b=bfAwZrj=bCAA@mail.gmail.com>
        <20230404101201epcms1p615a6365e64fc6e0a0fa203d41404940c@epcms1p6>
        <CGME20230403104617epcms1p383bacbca705c0d7e4fffca6833050e42@epcms1p1>
Precedence: bulk

>On Tue 2023-04-04 19:12:01, Jaewon Kim wrote:
>> >From: Jaewon Kim
>> >> Sent: 03 April 2023 15:40
>> >...
>> >> I wanted to print phys_addr_t  type value only when kptr_restrict sysctl is
>> >> allowed. So I thought I could use %pK for that purpose. And the physical
>> >> address is not that long. I wanted to make that length short like 9 hex.
>> >
>> >Isn't that is the wrong format for physical addresses anyway?
>> >They can be larger than virtual ones (eg x86 with PAE).
>> 
>> Yeah, correct. I just used %pK to hide physical address, I thought it could be
>> leak in security perspective. Could you give me advice how I can hide the
>> address by default and look the address if kptr_restrict allow it?
>
>Could you please send a patch that would show what value you want to print?
>
>The initial mail mentioned converting %09lx to %09pK in some driver.
>Then it included a warning when compiling from mm/page_alloc.o
>
                                                                                                                                                       O
Oh I just found something I'm interested. I was printing rmem->base and
rmem->name and wanted to hide the rmem->base. The commit aeb9267eb6b1 
("of: reserved-mem: print out reserved-mem details during boot - v6.3-rc1")
just used %pa. If %pa is not good enough in security perspecitve, I think
I can use %pa.

Yes it was just my curiosity. I don't actually need the length.

I'm OK now.
Thank you 

>Honestly, I think that you could just use %pK or %p. IMHO, it does not
>make sense to optimize it for the length.
>
>Anyway, there is still the question if the address is really worth
>printing. Will it really help to locate a potential problem?
>
>Best Regards,
>Petr