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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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