On Tuesday, July 26, 2016 01:33:02 PM Kees Cook wrote:

On Tue, Jul 26, 2016 at 1:24 PM, Rafael J. Wysocki [off-list ref] wrote:

quoted

On Tuesday, July 26, 2016 04:04:42 PM Borislav Petkov wrote:

quoted

On Tue, Jul 26, 2016 at 01:32:28PM +0200, Rafael J. Wysocki wrote:

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Hi,

The following commit:

commit 13523309495cdbd57a0d344c0d5d574987af007f
Author: Josh Poimboeuf [off-list ref]
Date:   Thu Jan 21 16:49:21 2016 -0600

    x86/asm/acpi: Create a stack frame in do_suspend_lowlevel()

    do_suspend_lowlevel() is a callable non-leaf function which doesn't
    honor CONFIG_FRAME_POINTER, which can result in bad stack traces.

    Create a stack frame for it when CONFIG_FRAME_POINTER is enabled.

is reported to cause a resume-from-hibernation regression due to an attempt
to execute an NX page (we've seen quite a bit of that recently).

I'm asking the reporter to try 4.7, but if the problem is still there, we'll
need to revert the above I'm afraid.

So I can't resume properly from disk too, on the Intel laptop this time. Top
commit is from tip/master:

commit 516f48acf59722429acd323b3d283f74f02891fe (refs/remotes/tip/master)
Merge: a4823bbffc96 dd9506954539
Author: Ingo Molnar [off-list ref]
Date:   Mon Jul 25 08:39:43 2016 +0200

    Merge branch 'linus'


So I thought it might be Josh's patch above and reverted it. No joy.

Then I remembered that I enabled CONFIG_RANDOMIZE_MEMORY for the
microcode loader breakage which we've been debugging. Turned that off
and machine resumes fine again.

Well, I wasn't aware of *another* flavor of ASLR in the works.  And there
was no hope it would not break hibernation if you asked me.

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It looks like

  0483e1fa6e09 ("x86/mm: Implement ASLR for kernel memory regions")

broke a bunch of things. Off the top of my head, we probably should make
suspend to disk and CONFIG_RANDOMIZE_MEMORY mutually exclusive, like it
was the case with ASLR previously, AFAIR.

Please no.

First off, it should be perfectly possible to make hibernation work along
with this new variant of ASLR.  Second, quite obviously, the author of these
ASLR changes had not done sufficient research to estimate the possible
impact of them.

I think that's a bit unfair: Thomas did a lot of testing, and it has
been living in -next for a while.

Well, with all due respect, "a lot of testing" is not quite the same thing as
"sufficient research" IMO.

It should be known (at least from experience) that hibernation on x86-64 doesn't
play well with ASLR quite as a rule, so it would be good to at least check that
particular thing or CC a relevant person (ie. me).

Or even ask me on IRC for that matter.  Give me a heads up ahead of time.

But no.  I'm still on the receiving end of the "hibernation doesn't work with
ASLR" story which was entirely avoidable this time around.  Sigh.

quoted

Honestly, I don't think it is a good idea to introduce random Kconfig options
for working around cases in which the author of some changes cannot be bothered
with doing things right.  Even if that is security.

I would agree: let's try to get this fixed soon.

quoted

So IMO, either we should fix the problem, or that whole new ASLR stuff should
be reverted.

I think I know how to fix it, but I won't be able to get to that before the
next week.  I guess it can wait till then, though.

Thomas, will you have some time to examine this and estimate the work for a fix?

FWIW, my hunch ATM is that you need to look at the "Set up the direct mapping
from scratch" loop in set_up_temporary_mappings() and make it do the right
thing when the new ASLR stuff is enabled.

Thanks,
Rafael