linux-kernel - Re: [Resend][PATCH] x86/power/64: Always create temporary identity mapping correctly

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Message-ID: <CAJZ5v0hVNh7oA+1MvDbx-GY+nd82Whb4=7AT+e=LicOxs0qzkg@mail.gmail.com>
Date:	Thu, 11 Aug 2016 03:35:39 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Thomas Garnier <thgarnie@...gle.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Jiri Kosina <jikos@...nel.org>, Borislav Petkov <bp@...e.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>, Pavel Machek <pavel@....cz>,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [Resend][PATCH] x86/power/64: Always create temporary identity
 mapping correctly

On Thu, Aug 11, 2016 at 3:17 AM, Thomas Garnier <thgarnie@...gle.com> wrote:
> On Wed, Aug 10, 2016 at 5:35 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
>> On Wed, Aug 10, 2016 at 11:59 PM, Jiri Kosina <jikos@...nel.org> wrote:
>>> On Wed, 10 Aug 2016, Rafael J. Wysocki wrote:
>>>
>>>> So I used your .config to generate one for my test machine and with
>>>> that I can reproduce.
>>>
>>> Was that the config I've sent, or did Boris provide one as well? Which one
>>> are you able to reproduce with please?
>>
>> It's the Boris' one.
>>
>> Moreover, I have found the options that make the difference: unsetting
>> CONFIG_PROVE_LOCKING and CONFIG_DEBUG_LOCK_ALLOC (which also will
>> unset CONFIG_LOCKDEP AFAICS) in it makes hibernation work again with
>> CONFIG_RANDOMIZE_MEMORY set and with the $subject patch applied.
>>
>> Unbelievable, but that's what I'm seeing.
>
> Nice find!
>
>>
>> Now, that leads to a few questions:
>>
>> - How does lockdep change the picture so it matters for hibernation?
>> - Why is hibernation the only piece that's affected?
>> - Why is RANDOMIZE_MEMORY necessary to make this breakage show up?
>>
>> Thomas, any ideas?
>
> No idea so far. I will investigate though.
>
> We had an unrelated issue with CONFIG_DEBUG_PAGEALLOC on early boot. I
> don't think it was related because it was on early boot and with
> certain e820 memory layout (and PUD randomization that I disabled on
> the previous patch test). The fix is on tip:
> http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?id=fb754f958f8e46202c1efd7f66d5b3db1208117d

Well, I don't think this is related.

In the meantime, I went back to my original .config and verified that
setting CONFIG_DEBUG_LOCK_ALLOC in it caused hibernation to fail (with
CONFIG_RANDOMIZE_MEMORY set and with the $subject patch applied), so
this really matters somehow.

Besides, now that I have a reproducer, I can check various other
things and for example this change (sorry for broken whitespace):

Index: linux-pm/arch/x86/mm/kaslr.c
===================================================================
--- linux-pm.orig/arch/x86/mm/kaslr.c
+++ linux-pm/arch/x86/mm/kaslr.c
@@ -122,7 +122,7 @@ void __init kernel_randomize_memory(void
         prandom_bytes_state(&rand_state, &rand, sizeof(rand));
         entropy = (rand % (entropy + 1)) & PUD_MASK;
         vaddr += entropy;
-        *kaslr_regions[i].base = vaddr;
+        *kaslr_regions[i].base += PUD_SIZE;

         /*
          * Jump the region and add a minimum padding based on

makes hibernation work for me again in the above configuration.  To
me, this means that the $subject patch works as expected and the
problem really is related to the vaddr value being too big.

Thanks,
Rafael