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

[Jiri Kosina <jikos@kernel.org>]

On Tue, 9 Aug 2016, Thomas Garnier wrote:

> >> Okay, I did one-by-one reverts, and the one above, i.e.
> >>
> >>       commit 021182e52fe01c1f7b126f97fd6ba048dc4234fd
> >>       Author: Thomas Garnier <thgarnie@google.com>
> >>       Date:   Tue Jun 21 17:47:03 2016 -0700
> >>
> >>           x86/mm: Enable KASLR for physical mapping memory regions
> >>
> >> is the one that is the culprit on my machine. With this one reverted,
> >> resume hibernation doesn't reboot (tripple fault?), but proceeds
> >> succesfully.
> 
> My .config is attached. It is basically defconfig (x86_64) + kvmconfig
> plus the following:
> 
> CONFIG_PHYSICAL_START=0x1000000
> CONFIG_RELOCATABLE=y
> CONFIG_RANDOMIZE_BASE=y
> CONFIG_X86_NEED_RELOCS=y
> CONFIG_PHYSICAL_ALIGN=0x1000000
> CONFIG_RANDOMIZE_MEMORY=y
> CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING=0xa
> CONFIG_X86_PTDUMP_CORE=y
> CONFIG_X86_PTDUMP=y
> CONFIG_KALLSYMS=y
> CONFIG_KALLSYMS_ALL=y
> CONFIG_KALLSYMS_ABSOLUTE_PERCPU=y
> CONFIG_KALLSYMS_BASE_RELATIVE=y
> CONFIG_PANIC_ON_OOPS=y
> CONFIG_KGDB=y
> CONFIG_EARLY_PRINTK=y
> CONFIG_EARLY_PRINTK_DBGP=y
> CONFIG_DEBUG_INFO=y
> CONFIG_DEBUG_INFO_DWARF4=y

The config I am reproducing the bug with (on thinkpad x200s) can be found 
at

	http://www.jikos.cz/jikos/junk/.config

Either later today or tomorrow I could test with the same physical start 
and align values you're using to see whether that'd make any difference.

> > As discussed with Rafael privately, I also tried this very patch
> > (x86/power/64: Always create temporary identity mapping correctly) on top
> > of the reverted revert of 021182e52fe01c1f7b1 (see the full log below),
> > but such kernel triple faults on resume as well.
> >
> > 87c38d2 x86/power/64: Always create temporary identity mapping correctly
> > 3cb504a Revert "Revert "x86/mm: Enable KASLR for physical mapping memory regions""
> > 758850d Revert "x86/mm: Enable KASLR for physical mapping memory regions"
> > 4a02dfb Revert "x86/mm: Enable KASLR for vmalloc memory regions"
> > 037863f Revert "x86/mm: Add memory hotplug support for KASLR memory randomization"
> > 3416a21 Revert "x86/mm: Do not reference phys addr beyond kernel"
> > 69227be Revert "mm: reorganize SLAB freelist randomization"
> > a1d8d71 Revert "mm: SLUB freelist randomization"
> >
> > IOW, 021182e52f introduces a bug for which there is no existing fix yet.
> 
> You mean it is something different from the previous KASLR bugs we saw?

No, I just wanted to explicitly point out that "x86/power/64: Always 
create temporary identity mapping correctly" is not a fix for this issue.

-- 
Jiri Kosina
SUSE Labs