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Date:   Tue, 4 Apr 2023 14:03:47 +0200
From:   Petr Mladek <pmladek@suse.com>
To:     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>
Subject: Re: [RFC] vsprintf: compile error on %09pK
Message-ID: <ZCwSIy5Tm0jAe1Ww@alley>
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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

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