linux-kernel - Re: [PATCH v2] livepatch: x86: make kASLR logic more accurate

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Message-ID: <alpine.LNX.2.00.1504252239540.16113@pobox.suse.cz>
Date:	Sat, 25 Apr 2015 22:42:52 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
cc:	Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] livepatch: x86: make kASLR logic more accurate

On Fri, 24 Apr 2015, Josh Poimboeuf wrote:

> >  #if defined(CONFIG_RANDOMIZE_BASE)
> > -	/* KASLR is enabled, disregard old_addr from user */
> > -	func->old_addr = 0;
> > +	/* If KASLR has been enabled, adjust old_addr accordingly */
> > +	if (kaslr_enabled())
> > +		func->old_addr += klp_vmlinux_relocation_offset();
> >  #endif
> 
> Can we remove the #ifdef now?  It would probably be better to have an
> #ifdef in asm/setup.h for the kaslr_enabled() definition.

If we do that, we force all architectures that support (now, or at any 
point in the future) live patching to provide kaslr_enabled(), 
klp_vmlinux_relocation_offset() (or however it will be called), etc (even 
if they don't care a bit about kASLR) I would like to avoid that; it seems 
really unnecessary maintainance overhead imposed on archs.

Thanks,

-- 
Jiri Kosina
SUSE Labs
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