Re: [PATCH v6 00/12] implement KASLR for powerpc/fsl_booke/32
From: Scott Wood
Date: Wed Aug 28 2019 - 01:00:11 EST
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.