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

[Ard Biesheuvel]

On 18 August 2017 at 16:24, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> On 18 August 2017 at 16:22, Catalin Marinas <catalin.marinas at arm.com> wrote:
>> 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.
>>
>
> Ah ok. I did not realize QEMU supports 16 KB pages in that case. Nice!
>
> However, that makes it rather difficult to reproduce on my side.

Are you booting with an initrd?