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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