linux-kernel - Re: [PATCH v3 5/6] powerpc/fsl_booke/64: clear the original kernel if randomized

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Message-ID: <71e25bac-bdf6-a754-c0f8-c9d99a393085@huawei.com>
Date:   Thu, 5 Mar 2020 11:20:38 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     Scott Wood <oss@...error.net>, <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>
CC:     <linux-kernel@...r.kernel.org>, <zhaohongjiang@...wei.com>
Subject: Re: [PATCH v3 5/6] powerpc/fsl_booke/64: clear the original kernel if
 randomized



在 2020/3/5 5:53, Scott Wood 写道:
> On Thu, 2020-02-06 at 10:58 +0800, Jason Yan wrote:
>> The original kernel still exists in the memory, clear it now.
>>
>> Signed-off-by: Jason Yan <yanaijie@...wei.com>
>> Cc: Scott Wood <oss@...error.net>
>> 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>
>> ---
>>   arch/powerpc/mm/nohash/kaslr_booke.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/mm/nohash/kaslr_booke.c
>> b/arch/powerpc/mm/nohash/kaslr_booke.c
>> index c6f5c1db1394..ed1277059368 100644
>> --- a/arch/powerpc/mm/nohash/kaslr_booke.c
>> +++ b/arch/powerpc/mm/nohash/kaslr_booke.c
>> @@ -378,8 +378,10 @@ notrace void __init kaslr_early_init(void *dt_ptr,
>> phys_addr_t size)
>>   	unsigned int *__kaslr_offset = (unsigned int *)(KERNELBASE + 0x58);
>>   	unsigned int *__run_at_load = (unsigned int *)(KERNELBASE + 0x5c);
>>   
>> -	if (*__run_at_load == 1)
>> +	if (*__run_at_load == 1) {
>> +		kaslr_late_init();
>>   		return;
>> +	}
> 
> What if you're here because kexec set __run_at_load (or
> CONFIG_RELOCATABLE_TEST is enabled), not because kaslr happened?
> 

Nothing will happen because kaslr_late_init() only clears memory when
kernstart_virt_addr is not KERNELBASE. When __run_at_load is set then
KASLR will not take effect.

> -Scott
> 
> 
> 
> .
>