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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
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