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

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