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Message-ID: <20190828045454.GB17757@home.buserror.net>
Date: Tue, 27 Aug 2019 23:54:54 -0500
From: Scott Wood <oss@...error.net>
To: Jason Yan <yanaijie@...wei.com>
Cc: mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
diana.craciun@....com, christophe.leroy@....fr,
benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com,
keescook@...omium.org, kernel-hardening@...ts.openwall.com,
wangkefeng.wang@...wei.com, linux-kernel@...r.kernel.org,
jingxiangfeng@...wei.com, zhaohongjiang@...wei.com,
thunder.leizhen@...wei.com, fanchengyang@...wei.com,
yebin10@...wei.com
Subject: Re: [PATCH v6 06/12] powerpc/fsl_booke/32: implement KASLR
infrastructure
On Fri, Aug 09, 2019 at 06:07:54PM +0800, Jason Yan wrote:
> This patch add support to boot kernel from places other than KERNELBASE.
> 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.
>
> The offset of the kernel was not randomized yet(a fixed 64M is set). We
> will randomize it in the next patch.
>
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> Cc: Diana Craciun <diana.craciun@....com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Christophe Leroy <christophe.leroy@....fr>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Kees Cook <keescook@...omium.org>
> Tested-by: Diana Craciun <diana.craciun@....com>
> Reviewed-by: Christophe Leroy <christophe.leroy@....fr>
> ---
> arch/powerpc/Kconfig | 11 ++++
> arch/powerpc/kernel/Makefile | 1 +
> arch/powerpc/kernel/early_32.c | 2 +-
> arch/powerpc/kernel/fsl_booke_entry_mapping.S | 17 +++--
> arch/powerpc/kernel/head_fsl_booke.S | 13 +++-
> arch/powerpc/kernel/kaslr_booke.c | 62 +++++++++++++++++++
> arch/powerpc/mm/mmu_decl.h | 7 +++
> arch/powerpc/mm/nohash/fsl_booke.c | 7 ++-
> 8 files changed, 105 insertions(+), 15 deletions(-)
> create mode 100644 arch/powerpc/kernel/kaslr_booke.c
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 77f6ebf97113..710c12ef7159 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -548,6 +548,17 @@ config RELOCATABLE
> setting can still be useful to bootwrappers that need to know the
> load address of the kernel (eg. u-boot/mkimage).
>
> +config RANDOMIZE_BASE
> + bool "Randomize the address of the kernel image"
> + depends on (FSL_BOOKE && FLATMEM && PPC32)
> + depends on RELOCATABLE
> + help
> + Randomizes the virtual address at which the kernel image is
> + loaded, as a security feature that deters exploit attempts
> + relying on knowledge of the location of kernel internals.
> +
> + If unsure, say N.
> +
Why is N the safe default (other than concerns about code maturity,
though arm64 and mips don't seem to have updated this recommendation
after several years)? On x86 this defaults to Y.
> diff --git a/arch/powerpc/kernel/fsl_booke_entry_mapping.S b/arch/powerpc/kernel/fsl_booke_entry_mapping.S
> index f4d3eaae54a9..641920d4f694 100644
> --- a/arch/powerpc/kernel/fsl_booke_entry_mapping.S
> +++ b/arch/powerpc/kernel/fsl_booke_entry_mapping.S
> @@ -155,23 +155,22 @@ skpinv: addi r6,r6,1 /* Increment */
>
> #if defined(ENTRY_MAPPING_BOOT_SETUP)
>
> -/* 6. Setup KERNELBASE mapping in TLB1[0] */
> +/* 6. Setup kernstart_virt_addr mapping in TLB1[0] */
> lis r6,0x1000 /* Set MAS0(TLBSEL) = TLB1(1), ESEL = 0 */
> mtspr SPRN_MAS0,r6
> lis r6,(MAS1_VALID|MAS1_IPROT)@h
> ori r6,r6,(MAS1_TSIZE(BOOK3E_PAGESZ_64M))@l
> mtspr SPRN_MAS1,r6
> - lis r6,MAS2_VAL(PAGE_OFFSET, BOOK3E_PAGESZ_64M, MAS2_M_IF_NEEDED)@h
> - ori r6,r6,MAS2_VAL(PAGE_OFFSET, BOOK3E_PAGESZ_64M, MAS2_M_IF_NEEDED)@l
> - mtspr SPRN_MAS2,r6
> + lis r6,MAS2_EPN_MASK(BOOK3E_PAGESZ_64M)@h
> + ori r6,r6,MAS2_EPN_MASK(BOOK3E_PAGESZ_64M)@l
> + and r6,r6,r20
> + ori r6,r6,MAS2_M_IF_NEEDED@l
> + mtspr SPRN_MAS2,r6
Please use tabs rather than spaces between the mnemonic and the
arguments.
It looks like that was the last user of MAS2_VAL so let's remove it.
> diff --git a/arch/powerpc/kernel/kaslr_booke.c b/arch/powerpc/kernel/kaslr_booke.c
> new file mode 100644
> index 000000000000..f8dc60534ac1
> --- /dev/null
> +++ b/arch/powerpc/kernel/kaslr_booke.c
Shouldn't this go under arch/powerpc/mm/nohash?
> +/*
> + * To see if we need to relocate the kernel to a random offset
> + * void *dt_ptr - address of the device tree
> + * phys_addr_t size - size of the first memory block
> + */
> +notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
> +{
> + unsigned long tlb_virt;
> + phys_addr_t tlb_phys;
> + unsigned long offset;
> + unsigned long kernel_sz;
> +
> + kernel_sz = (unsigned long)_end - KERNELBASE;
Why KERNELBASE and not kernstart_addr?
> +
> + offset = kaslr_choose_location(dt_ptr, size, kernel_sz);
> +
> + if (offset == 0)
> + return;
> +
> + kernstart_virt_addr += offset;
> + kernstart_addr += offset;
> +
> + is_second_reloc = 1;
> +
> + if (offset >= SZ_64M) {
> + tlb_virt = round_down(kernstart_virt_addr, SZ_64M);
> + tlb_phys = round_down(kernstart_addr, SZ_64M);
If kernstart_addr wasn't 64M-aligned before adding offset, then "offset
>= SZ_64M" is not necessarily going to detect when you've crossed a
mapping boundary.
> +
> + /* Create kernel map to relocate in */
> + create_tlb_entry(tlb_phys, tlb_virt, 1);
> + }
> +
> + /* Copy the kernel to it's new location and run */
> + memcpy((void *)kernstart_virt_addr, (void *)KERNELBASE, kernel_sz);
> +
> + reloc_kernel_entry(dt_ptr, kernstart_virt_addr);
> +}
After copying, call flush_icache_range() on the destination.
> diff --git a/arch/powerpc/mm/nohash/fsl_booke.c b/arch/powerpc/mm/nohash/fsl_booke.c
> index 556e3cd52a35..2dc27cf88add 100644
> --- a/arch/powerpc/mm/nohash/fsl_booke.c
> +++ b/arch/powerpc/mm/nohash/fsl_booke.c
> @@ -263,7 +263,8 @@ void setup_initial_memory_limit(phys_addr_t first_memblock_base,
> int __initdata is_second_reloc;
> notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
> {
> - unsigned long base = KERNELBASE;
> + unsigned long base = kernstart_virt_addr;
> + phys_addr_t size;
>
> kernstart_addr = start;
> if (is_second_reloc) {
> @@ -291,7 +292,7 @@ notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
> start &= ~0x3ffffff;
> base &= ~0x3ffffff;
> virt_phys_offset = base - start;
> - early_get_first_memblock_info(__va(dt_ptr), NULL);
> + early_get_first_memblock_info(__va(dt_ptr), &size);
> /*
> * We now get the memstart_addr, then we should check if this
> * address is the same as what the PAGE_OFFSET map to now. If
> @@ -316,6 +317,8 @@ notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
> /* We should never reach here */
> panic("Relocation error");
> }
> +
> + kaslr_early_init(__va(dt_ptr), size);
Are you assuming that available memory starts at physical address zero?
This isn't true of some partitioning scenarios, or in a kdump crash
kernel.
-Scott
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