[PATCH] arm64: kaslr: Adjust the offset to avoid Image across alignment boundary

[Catalin Marinas]

On Fri, Aug 18, 2017 at 04:20:16PM +0100, Ard Biesheuvel wrote:
> On 18 August 2017 at 16:19, Catalin Marinas <catalin.marinas at arm.com> wrote:
> > On Fri, Aug 18, 2017 at 04:04:34PM +0100, Catalin Marinas wrote:
> >> With 16KB pages and a kernel Image larger than 16MB, the current
> >> kaslr_early_init() logic for avoiding mappings across swapper table
> >> boundaries fails since increasing the offset by kimg_sz just moves the
> >> problem to the next boundary.
> >>
> >> This patch decreases the offset by the boundary overflow amount, with
> >> slight risk of reduced entropy as the kernel is more likely to be found
> >> at kimg_sz below a swapper table boundary.
> >>
> >> Trying-to-fix: afd0e5a87670 ("arm64: kaslr: Fix up the kernel image alignment")
> >> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> >> Cc: Mark Rutland <mark.rutland at arm.com>
> >> Cc: Will Deacon <will.deacon at arm.com>
> >> Cc: Neeraj Upadhyay <neeraju at codeaurora.org>
> >> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> >> ---
> >>
> >> While preparing this email, I noticed that the kernel eventually failed
> >> to boot, though after a lot more reboot iterations. Mark Rutland also
> >> managed to make the KASLR kernel fail to boot with 64K pages which
> >> wouldn't be explained by this patch.
> >>
> >> So, any suggestions are welcome. My testing method, qemu starting a
> >> guest in a loop with virtio-rng-pci.
> >
> > Apparently, the booting gets much more stable if I disable the physical
> > relocation in arm64-stub.c (but keep the virtual one with the fix in
> > this patch). So I guess we are chasing two different issues.
> 
> So this is using QEMU with 16k pages support?

Qemu running on a ThunderX, so native KVM support.

-- 
Catalin