linux-kernel - Re: [LKP] [x86/mm/ASLR] f47233c2d34: WARNING: CPU: 0 PID: 1 at arch/x86/mm/ioremap.c:63 __ioremap_check

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Message-ID: <20150228192009.GA2727@codeblueprint.co.uk>
Date:	Sat, 28 Feb 2015 19:20:09 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Borislav Petkov <bp@...e.de>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Jiri Kosina <jkosina@...e.cz>, Ingo Molnar <mingo@...nel.org>,
	Huang Ying <ying.huang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, LKP ML <lkp@...org>,
	x86-ml <x86@...nel.org>, Dave Young <dyoung@...hat.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [LKP] [x86/mm/ASLR] f47233c2d34: WARNING: CPU: 0 PID: 1 at
 arch/x86/mm/ioremap.c:63 __ioremap_check_ram+0x445/0x4a0()

On Sat, 28 Feb, at 11:50:49AM, Borislav Petkov wrote:
> 
> Yeah, too many hmms means this still needed staring at to find out what
> exactly the problem is. And the problem is that allocating that struct
> setup_data statically in arch/x86/boot/compressed/aslr.c works only by
> chance, when the kernel decompressing doesn't overwrite that memory.

Doing a static allocation is fine, and the memory is even reserved from
being overwritten via memblock_x86_reserve_range_setup_data(), but it
looks like that reservation gets dropped before
get_setup_data_total_num() runs, which is what is causing ioremap() to
complain - it really is usable RAM we're trying to ioremap().

Dropping the reservation looks to happen in memblock_x86_fill(), because
you'll note that we explicitly reserve the boot services regions
immediately after memblock_x86_fill() in setup_arch().

What isn't clear right now is why the ioremap() warning isn't triggering
for a bunch of other callsites that get this wrong, i.e.
pcibios_add_device().

-- 
Matt Fleming, Intel Open Source Technology Center
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