Re: [PATCH v6 00/12] implement KASLR for powerpc/fsl_booke/32

From: Jason Yan <yanaijie@huawei.com>
To: Scott Wood <oss@buserror.net>, <mpe@ellerman.id.au>,
	<linuxppc-dev@lists.ozlabs.org>, <diana.craciun@nxp.com>,
	<christophe.leroy@c-s.fr>, <benh@kernel.crashing.org>,
	<paulus@samba.org>, <npiggin@gmail.com>, <keescook@chromium.org>,
	<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>
Subject: Re: [PATCH v6 00/12] implement KASLR for powerpc/fsl_booke/32
Date: Thu, 29 Aug 2019 09:57:20 +0800	[thread overview]
Message-ID: <923983fc-364d-440d-5c3a-3d3d6de60d14@huawei.com> (raw)
In-Reply-To: <a39b81562bcdeda7ffe0c2c29a60ff08c77047a6.camel@buserror.net>

On 2019/8/28 12:05, Scott Wood wrote:
> 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.
> 

Not yet. I will test this kind of cases in the next days. Thank you so
much. If there are any other corner cases that have to be tested, please
let me know.

>>   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
> 
> 
> 
> .
> 