linux-kernel - Re: [PATCH v6 06/12] powerpc/fsl_booke/32: implement KASLR infrastructure

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Message-ID: <2db76c55-df5f-5ca8-f0a6-bcee75b8edaa@c-s.fr>
Date:   Wed, 28 Aug 2019 07:47:51 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Scott Wood <oss@...error.net>, Jason Yan <yanaijie@...wei.com>
Cc:     mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        diana.craciun@....com, 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



Le 28/08/2019 à 06:54, Scott Wood a écrit :
> 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/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.

Function copy_and_flush() does the copy and the flush. I think it should 
be used instead of memcpy() + flush_icache_range()

Christophe