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

[catalin.marinas@arm.com (Catalin Marinas)]

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@linaro.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
> Signed-off-by: Catalin Marinas <catalin.marinas@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.

-- 
Catalin