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

[Ard Biesheuvel]

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?