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From:   Scott Wood <oss@buserror.net>
To:     Jason Yan <yanaijie@huawei.com>, mpe@ellerman.id.au,
        linuxppc-dev@lists.ozlabs.org, diana.craciun@nxp.com,
        christophe.leroy@c-s.fr, benh@kernel.crashing.org,
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        kernel-hardening@lists.openwall.com
Cc:     wangkefeng.wang@huawei.com, linux-kernel@vger.kernel.org,
        jingxiangfeng@huawei.com, zhaohongjiang@huawei.com,
        thunder.leizhen@huawei.com, fanchengyang@huawei.com,
        yebin10@huawei.com
Date:   Tue, 27 Aug 2019 23:05:30 -0500
In-Reply-To: <20190809100800.5426-1-yanaijie@huawei.com>
References: <20190809100800.5426-1-yanaijie@huawei.com>
Organization: Red Hat
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Subject: Re: [PATCH v6 00/12] implement KASLR for powerpc/fsl_booke/32
Sender: linux-kernel-owner@vger.kernel.org
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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