Re: [RFC PATCH 00/10] implement KASLR for powerpc/fsl_booke/32

From: Jason Yan
Date: Thu Jul 25 2019 - 14:03:54 EST

Hi all, any comments?

On 2019/7/17 16:06, 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. 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

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.

We will use the first 512M of the low memory to randomize the kernel
image. The memory will be split in 64M zones. We will use the lower 8
bit of the entropy to decide the index of the 64M zone. Then we chose a
16K aligned offset inside the 64M zone to put the kernel in.


|--> 64M <--|
| |
+---------------+ +----------------+---------------+
| |....| |kernel| | |
+---------------+ +----------------+---------------+
| |
|-----> offset <-----|


We also check if we will overlap with some areas like the dtb area, the
initrd area or the crashkernel area. If we cannot find a proper area,
kaslr will be disabled and boot from the original kernel.

Jason Yan (10):
powerpc: unify definition of M_IF_NEEDED
powerpc: move memstart_addr and kernstart_addr to init-common.c
powerpc: introduce kimage_vaddr to store the kernel base
powerpc/fsl_booke/32: introduce create_tlb_entry() helper
powerpc/fsl_booke/32: introduce reloc_kernel_entry() helper
powerpc/fsl_booke/32: implement KASLR infrastructure
powerpc/fsl_booke/32: randomize the kernel image offset
powerpc/fsl_booke/kaslr: clear the original kernel if randomized
powerpc/fsl_booke/kaslr: support nokaslr cmdline parameter
powerpc/fsl_booke/kaslr: dump out kernel offset information on panic

arch/powerpc/Kconfig | 11 +
arch/powerpc/include/asm/nohash/mmu-book3e.h | 10 +
arch/powerpc/include/asm/page.h | 7 +
arch/powerpc/kernel/Makefile | 1 +
arch/powerpc/kernel/early_32.c | 2 +-
arch/powerpc/kernel/exceptions-64e.S | 10 -
arch/powerpc/kernel/fsl_booke_entry_mapping.S | 23 +-
arch/powerpc/kernel/head_fsl_booke.S | 61 ++-
arch/powerpc/kernel/kaslr_booke.c | 439 ++++++++++++++++++
arch/powerpc/kernel/machine_kexec.c | 1 +
arch/powerpc/kernel/misc_64.S | 5 -
arch/powerpc/kernel/setup-common.c | 23 +
arch/powerpc/mm/init-common.c | 7 +
arch/powerpc/mm/init_32.c | 5 -
arch/powerpc/mm/init_64.c | 5 -
arch/powerpc/mm/mmu_decl.h | 10 +
arch/powerpc/mm/nohash/fsl_booke.c | 8 +-
17 files changed, 580 insertions(+), 48 deletions(-)
create mode 100644 arch/powerpc/kernel/kaslr_booke.c