linux-kernel - Re: [PATCH V11 4/5] vsprintf: add printk specifier %px

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Message-ID: <CA+55aFzMydq1TizkPOjZmRb_eKtHCk3w-xdO-Ce2jw9tu3bsGg@mail.gmail.com>
Date:   Tue, 5 Dec 2017 17:59:16 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        "Tobin C. Harding" <me@...in.cc>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "Theodore Ts'o" <tytso@....edu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tycho Andersen <tycho@...ho.ws>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        Tejun Heo <tj@...nel.org>,
        Jordan Glover <Golden_Miller83@...tonmail.ch>,
        Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <wilal.deacon@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        Radim Krcmár <rkrcmar@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH V11 4/5] vsprintf: add printk specifier %px

On Tue, Dec 5, 2017 at 5:36 PM, Sergey Senozhatsky
<sergey.senozhatsky.work@...il.com> wrote:
> I see some %p-s being used in _supposedly_ important output,
> like arch/x86/mm/fault.c
>
> show_fault_oops(struct pt_regs *regs, unsigned long error_code,
>                 unsigned long address)
> ...
>         printk(KERN_CONT " at %p\n", (void *) address);
>         printk(KERN_ALERT "IP: %pS\n", (void *)regs->ip);

So %pS isn't %p, and shows the symbolic name.

But yes, that "at %p" should definitely be %px.

In fact, it used to be a "%08lx" - and the value we print out is
"unsigned long - but then when we unified the 32- and 64-bit
architectures, using "%p" and a cast was a convenient way to unify the
32-bit %08lx and the 16-bit %016lx formats.

Will fix.

> a quick %p grep gives me the following list:
...
> or is it OK to show hashes instead of pgd or pmd pointers?

So my gut feel is that those printouts should probably just be
removed. They have some very old historical reasons: we've printed out
the page directory pointers (and followed the page tables) since at
least back in the 1.1.x days. This is from the 1.1.7 patch, back when
mm/memory.c was all about x86:

+       printk(KERN_ALERT "current->tss.cr3 = %08lx, %%cr3 = %08lx\n",
+               current->tss.cr3, user_esp);
+       user_esp = ((unsigned long *) user_esp)[address >> 22];
+       printk(KERN_ALERT "*pde = %08lx\n", user_esp);

so it's more historical than sensible, I think.

               Linus