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Message-ID: <de603506-5c4e-4ca3-bd77-e3a69af9faef@huawei.com>
Date: Wed, 28 Aug 2019 19:03:11 +0800
From: Jason Yan <yanaijie@...wei.com>
To: Scott Wood <oss@...error.net>
CC: <wangkefeng.wang@...wei.com>, <keescook@...omium.org>,
<kernel-hardening@...ts.openwall.com>, <thunder.leizhen@...wei.com>,
<linux-kernel@...r.kernel.org>, <npiggin@...il.com>,
<jingxiangfeng@...wei.com>, <diana.craciun@....com>, <paulus@...ba.org>,
<zhaohongjiang@...wei.com>, <fanchengyang@...wei.com>,
<linuxppc-dev@...ts.ozlabs.org>, <yebin10@...wei.com>
Subject: Re: [PATCH v6 06/12] powerpc/fsl_booke/32: implement KASLR
infrastructure
On 2019/8/28 12:54, Scott Wood wrote:
> 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.
>
Actually I would like to set this default Y. I was just wondering if
people like this feature or not at the beginning so I had to be more
careful.
>> 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.
>
OK.
>> 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?
>
Did you mean kernstart_virt_addr? It should be kernstart_virt_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.
>
OK
>> 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.
>
I'm not assuming that but I haven't tested that case for now. I will
reconsider and test these scenarios and fix all bugs.
> -Scott
>
> .
>
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