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

From: Scott Wood
Date: Wed Aug 28 2019 - 00:12:25 EST

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).