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Date: Mon, 29 Jul 2019 14:30:15 +0000
From: Diana Madalina Craciun <diana.craciun@....com>
To: Jason Yan <yanaijie@...wei.com>, "mpe@...erman.id.au"
<mpe@...erman.id.au>, "linuxppc-dev@...ts.ozlabs.org"
<linuxppc-dev@...ts.ozlabs.org>, "christophe.leroy@....fr"
<christophe.leroy@....fr>, "benh@...nel.crashing.org"
<benh@...nel.crashing.org>, "paulus@...ba.org" <paulus@...ba.org>,
"npiggin@...il.com" <npiggin@...il.com>, "keescook@...omium.org"
<keescook@...omium.org>, "kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"wangkefeng.wang@...wei.com" <wangkefeng.wang@...wei.com>,
"yebin10@...wei.com" <yebin10@...wei.com>, "thunder.leizhen@...wei.com"
<thunder.leizhen@...wei.com>, "jingxiangfeng@...wei.com"
<jingxiangfeng@...wei.com>, "fanchengyang@...wei.com"
<fanchengyang@...wei.com>
Subject: Re: [RFC PATCH 00/10] implement KASLR for powerpc/fsl_booke/32
Reviewed-by: Diana Craciun <diana.craciun@....com>
Tested-by: Diana Craciun <diana.craciun@....com>
On 7/17/2019 10:49 AM, 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
> 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.
>
> 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.
>
> KERNELBASE
>
> |--> 64M <--|
> | |
> +---------------+ +----------------+---------------+
> | |....| |kernel| | |
> +---------------+ +----------------+---------------+
> | |
> |-----> offset <-----|
>
> kimage_vaddr
>
> 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
>
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