[PATCH v5sub2 0/8] arm64: implement virtual KASLR

[Catalin Marinas]

On Fri, Feb 05, 2016 at 06:38:33PM +0100, Ard Biesheuvel wrote:
> On 5 February 2016 at 18:32, Catalin Marinas <catalin.marinas at arm.com> wrote:
> > On Mon, Feb 01, 2016 at 02:35:03PM +0100, Ard Biesheuvel wrote:
> >> On 1 February 2016 at 14:09, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> >> > At the request of Catalin, this series has been split off from my series
> >> > 'arm64: implement support for KASLR v4' [1]. This sub-series deals with
> >> > creating a relocatable binary, and randomizing the virtual placement of
> >> > the kernel itself, the modules and the linear region based on entropy
> >> > supplied by the bootloader in the /chosen/kaslr-seed DT property.
> >> >
> >> > Changes since v4:
> >> > - add randomization of the linear region, i.e., if the linear region is
> >> >   substantially larger than the space spanned by RAM, the mapping of RAM
> >> >   is moved to a random offset inside the linear region.
> >> > - dropped the CRC check in kaslr_early_init(), since the only code that may
> >> >   modify .data through __fixmap_remap_fdt() is instrumentation that should
> >> >   deal with that correctly (For instance, the branch profiling records taken
> >> >   branches in structs allocated in .data, and these counts will not be reset
> >> >   to 0 between the first and the second call to __mmap_switched())
> >> > - add Mark's ack to patch #4
> >> >
> >>
> >> NOTE: I have omitted the relative kallsyms and relative extable
> >> patches, since they already queued in akpm's tree. However, while the
> >> kallsyms patch is merely an optimization, the extable patches are in
> >> fact required for correct operation, since the build time sorting does
> >> not work on absolute extables (this is due to the fact that the
> >> resolution of the relocations is deferred until runtime, and so the
> >> extable addresses are all zero at sorting time)
> >>
> >> http://ozlabs.org/~akpm/mmotm/broken-out/extable-add-support-for-relative-extables-to-search-and-sort-routines.patch
> >> http://ozlabs.org/~akpm/mmotm/broken-out/arm64-switch-to-relative-exception-tables.patch
> >
> > I'm still trying to get my head around how we merge those. Since I
> > assume akpm will push them during the merging window, part of your code
> > cannot be tested before.
> 
> Actually, my original idea was for akpm to take them as a late merge
> after rebasing to -rc1, since they touch a variety of architectures,
> but I am not sure if that came across.
> 
> You could always take the series through your tree instead, I guess?

They all have acks from maintainers, so that's an option.

> > Can we deselect CONFIG_BUILDTIME_EXTABLE_SORT temporarily while we use
> > absolute extable addresses? We patch them at boot-time and sort them
> > at run-time. Once the above patches go in, we can revert to build-time
> > extable sorting.
> 
> I suppose that would be possible, but I simply haven't tried. I
> noticed that ppc does not use build time extable sorting, that is why
> they don't need to scripts/extable patch while they do use PIE
> binaries.

I did a quick check with:

--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -22,7 +22,7 @@ config ARM64
 	select ARM_GIC_V3
 	select ARM_GIC_V3_ITS if PCI_MSI
 	select ARM_PSCI_FW
-	select BUILDTIME_EXTABLE_SORT
+	select BUILDTIME_EXTABLE_SORT if !RELOCATABLE
 	select CLONE_BACKWARDS
 	select COMMON_CLK
 	select CPU_PM if (SUSPEND || CPU_IDLE)

and it seems that extable entries end up in the relocation symbols but I
haven't fully checked the patching/sorting yet (it will probably be on
Monday).

-- 
Catalin