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Date: Fri, 08 Jan 2016 10:17:02 +0000
From: James Morse <james.morse@....com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC: linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com, will.deacon@....com,
catalin.marinas@....com, mark.rutland@....com, leif.lindholm@...aro.org,
keescook@...omium.org, linux-kernel@...r.kernel.org,
stuart.yoder@...escale.com, bhupesh.sharma@...escale.com, arnd@...db.de,
marc.zyngier@....com, christoffer.dall@...aro.org
Subject: Re: [PATCH v2 12/13] arm64: add support for relocatable kernel
Hi Ard!
On 30/12/15 15:26, Ard Biesheuvel wrote:
> This adds support for runtime relocation of the kernel Image, by
> building it as a PIE (ET_DYN) executable and applying the dynamic
> relocations in the early boot code.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 01a33e42ed70..ab582ee58b58 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -243,6 +253,16 @@ ENDPROC(stext)
> preserve_boot_args:
> mov x21, x0 // x21=FDT
>
> +#ifdef CONFIG_ARM64_RELOCATABLE_KERNEL
> + /*
> + * Mask off the bits of the random value supplied in x1 so it can serve
> + * as a KASLR displacement value which will move the kernel image to a
> + * random offset in the lower half of the VMALLOC area.
> + */
> + mov x23, #(1 << (VA_BITS - 2)) - 1
> + and x23, x23, x1, lsl #SWAPPER_BLOCK_SHIFT
> +#endif
I've managed to make this fail to boot by providing a seed that caused
the kernel to overlap a 1G boundary on a 4K system.
(It looks like your v3 may have the same issue - but I haven't tested it.)
> +
> adr_l x0, boot_args // record the contents of
> stp x21, x1, [x0] // x0 .. x3 at kernel entry
> stp x2, x3, [x0, #16]
Thanks!
James
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