linux-kernel - Re: [PATCH V8 0/2] printk: hash addresses printed with %p

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Message-ID: <20171102101449.GG7499@eros>
Date:   Thu, 2 Nov 2017 21:14:49 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        kernel-hardening@...ts.openwall.com,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tycho Andersen <tycho@...ker.com>,
        "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>,
        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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V8 0/2] printk: hash addresses printed with %p

On Thu, Nov 02, 2017 at 05:23:44PM +0900, Sergey Senozhatsky wrote:
> On (11/01/17 10:35), Tobin C. Harding wrote:
> [..]
> > Yes. The question has been raised will we be here again in 6 years time
> > trying to fix all the uses of %x. And there are already 29K uses of
> > %[xX] in tree, which of these are leaking addresses? This is why Linus'
> > has commented that really effort should be directed at finding the leaks
> > as they happen (in procfs, sysfs, dmesg) instead of fixing this in
> > the code.
> 
> got it. thanks.
> 
> > So far I haven't been able to come up with any meaningful way
> > to do this on 32 bit machines. There is a patch adding a script to catch
> > leaks on 64 bit machines in flight.
> 
> who is expected to run that script?

If one person runs it and finds one leaking address, I'd say it wast
worth writing. If a bunch of people with different set ups run it and we
find a bunch of leaking addresses, WIN!

Your comment did give me the idea of adding some output to the command
offering an email address to send suspicious output for those who do not
wish to investigate it further. I can put my email address if there is
not a better option. 

> BTW, can BPF/eBPF printk addresses?

I know absolutely zero about BPF/eBPF. I guess now is a good time to learn.

> > This patch needs to be a small part of a continued effort to stop the
> > leaks if we want to have any hope of stopping them.
> > 
> > If you have any suggestions on dealing with %x please do say. We have
> > code changes, compiler warnings, and checkpatch - none of which
> > immediately seem great.
> 
> hm... just a huge pile of if's
> 
> 	if (is_vmalloc_addr(addr))
> 		do_hashing(addr);
> 	else if (__module_address(addr))
> 		do_hashing(addr);
> 	else if (is_kernel(addr) || is_kernel_inittext(addr))
> 	...
> 
> but that's going to be really messy and "iffy".

This is the only suggestion we have so far.

thanks,
Tobin.