Date: Tue, 27 Aug 2019 23:59:56 -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 Tue, 2019-08-27 at 23:05 -0500, Scott Wood wrote: > On Fri, 2019-08-09 at 18:07 +0800, Jason Yan wrote: > > 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). OK, I see that kaslr-seed is used on some other platforms, though arm64 aborts KASLR if it doesn't get a seed. I'm not sure if that's better than a loud warning message (or if it was a conscious choice rather than just not having an alternative implemented), but silently using poor entropy for something like this seems bad. -Scott
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