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Message-ID: <a39b81562bcdeda7ffe0c2c29a60ff08c77047a6.camel@buserror.net>
Date: Tue, 27 Aug 2019 23:05:30 -0500
From: Scott Wood <oss@...error.net>
To: Jason Yan <yanaijie@...wei.com>, mpe@...erman.id.au,
linuxppc-dev@...ts.ozlabs.org, diana.craciun@....com,
christophe.leroy@....fr, benh@...nel.crashing.org, paulus@...ba.org,
npiggin@...il.com, keescook@...omium.org,
kernel-hardening@...ts.openwall.com
Cc: wangkefeng.wang@...wei.com, linux-kernel@...r.kernel.org,
jingxiangfeng@...wei.com, zhaohongjiang@...wei.com,
thunder.leizhen@...wei.com, fanchengyang@...wei.com, yebin10@...wei.com
Subject: Re: [PATCH v6 00/12] implement KASLR for powerpc/fsl_booke/32
On Fri, 2019-08-09 at 18:07 +0800, Jason Yan wrote:
> This series implements KASLR for powerpc/fsl_booke/32, as a security
> feature that deters exploit attempts relying on knowledge of the location
> of kernel internals.
>
> Since CONFIG_RELOCATABLE has already supported, what we need to do is
> map or copy kernel to a proper place and relocate.
Have you tested this with a kernel that was loaded at a non-zero address? I
tried loading a kernel at 0x04000000 (by changing the address in the uImage,
and setting bootm_low to 04000000 in U-Boot), and it works without
CONFIG_RANDOMIZE and fails with.
> Freescale Book-E
> parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1
> entries are not suitable to map the kernel directly in a randomized
> region, so we chose to copy the kernel to a proper place and restart to
> relocate.
>
> Entropy is derived from the banner and timer base, which will change every
> build and boot. This not so much safe so additionally the bootloader may
> pass entropy via the /chosen/kaslr-seed node in device tree.
How complicated would it be to directly access the HW RNG (if present) that
early in the boot? It'd be nice if a U-Boot update weren't required (and
particularly concerning that KASLR would appear to work without a U-Boot
update, but without decent entropy).
-Scott
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