Date: Fri, 8 Jan 2016 11:43:25 +0000 From: Mark Rutland <mark.rutland@....com> To: Ard Biesheuvel <ard.biesheuvel@...aro.org> Cc: "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, kernel-hardening@...ts.openwall.com, Will Deacon <will.deacon@....com>, Catalin Marinas <catalin.marinas@....com>, Leif Lindholm <leif.lindholm@...aro.org>, Kees Cook <keescook@...omium.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Stuart Yoder <stuart.yoder@...escale.com>, Sharma Bhupesh <bhupesh.sharma@...escale.com>, Arnd Bergmann <arnd@...db.de>, Marc Zyngier <marc.zyngier@....com>, Christoffer Dall <christoffer.dall@...aro.org> Subject: Re: [PATCH v2 11/13] arm64: allow kernel Image to be loaded anywhere in physical memory On Fri, Jan 08, 2016 at 12:34:18PM +0100, Ard Biesheuvel wrote: > On 8 January 2016 at 12:26, Mark Rutland <mark.rutland@....com> wrote: > > We might also want to consider if we need to determine whether or not > > the bootloader actually provided entropy, (and if we need a more general > > handshake between the bootlaoder and kernel to determine that kind of > > thing). > > Yes, that is interesting. We should also think about how to handle > 'nokaslr' if it appears on the command line, since in the !EFI case, > we will be way too late to parse this, and a capable kernel will > already be running from a randomized offset. That means it is the > bootloader's responsibility to ensure that the presence of 'nokaslr' > and the entropy in x1 are consistent with each other. Argh, I hadn't considered that. :( In the absence of a pre-kernel environment, the best thing we can do is probably to print a giant warning if 'nokaslr' is present but there was entropy (where that's determined based on some handshake/magic/flag). > >> Any memory described to the kernel (even that below the start of the > >> image) which is not marked as reserved from the kernel (e.g., with a > >> diff --git a/arch/arm64/include/asm/boot.h b/arch/arm64/include/asm/boot.h > >> index 81151b67b26b..984cb0fa61ce 100644 > >> --- a/arch/arm64/include/asm/boot.h > >> +++ b/arch/arm64/include/asm/boot.h > >> @@ -11,4 +11,9 @@ > >> #define MIN_FDT_ALIGN 8 > >> #define MAX_FDT_SIZE SZ_2M > >> > >> +/* > >> + * arm64 requires the kernel image to be 2 MB aligned > > > > Nit: The image is TEXT_OFFSET from that 2M-aligned base. > > s/image/mapping/? > > > > [...] > > > > Yep. I hate TEXT_OFFSET, did I mention that? I would also love to remove it, but I believe it's simply too late. :( Thanks, Mark.
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