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

[Rafael J. Wysocki]

On Tue, Aug 9, 2016 at 5:05 PM, Jiri Kosina <jikos@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
>> >>       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.

It is better to say that the $subject patch is not sufficient to fix
it, because I'm quite confident that it is necessary for that. :-)

Without the $subject patch kernel_ident_mapping_init() makes
assumptions that simply are not met in the randomized identity mapping
base case.  Moreover, hibernation works for Thomas with $subject patch
applied, but it doesn't without it.

So there is something else that we are missing.

I have a murky suspicion, but it is really weird.  Namely, what if
restore_jump_address in set_up_temporary_text_mapping() happens to be
covered by the restore kernel's identity mapping?  Then, the image
kernel's entry point may get overwritten by something else in
core_restore_code().

But is this possible even?  Thomas?

Anyway, I'll try to reproduce this issue later today.

Thanks,
Rafael