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Subject: Re: [PATCH v5 10/10] powerpc/fsl_booke/kaslr: dump out kernel offset
 information on panic
To:     Michael Ellerman <mpe@ellerman.id.au>,
        <linuxppc-dev@lists.ozlabs.org>, <diana.craciun@nxp.com>,
        <christophe.leroy@c-s.fr>, <benh@kernel.crashing.org>,
        <paulus@samba.org>, <npiggin@gmail.com>, <keescook@chromium.org>,
        <kernel-hardening@lists.openwall.com>
CC:     <linux-kernel@vger.kernel.org>, <wangkefeng.wang@huawei.com>,
        <yebin10@huawei.com>, <thunder.leizhen@huawei.com>,
        <jingxiangfeng@huawei.com>, <fanchengyang@huawei.com>,
        <zhaohongjiang@huawei.com>
References: <20190807065706.11411-1-yanaijie@huawei.com>
 <20190807065706.11411-11-yanaijie@huawei.com>
 <87zhklt9eg.fsf@concordia.ellerman.id.au>
From:   Jason Yan <yanaijie@huawei.com>
Message-ID: <9113cc5b-0e89-f423-712a-79220af82b92@huawei.com>
Date:   Thu, 8 Aug 2019 16:39:26 +0800
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On 2019/8/7 21:03, Michael Ellerman wrote:
> Jason Yan <yanaijie@huawei.com> writes:
>> When kaslr is enabled, the kernel offset is different for every boot.
>> This brings some difficult to debug the kernel. Dump out the kernel
>> offset when panic so that we can easily debug the kernel.
> 
> Some of this is taken from the arm64 version right? Please say so when
> you copy other people's code.
> 

No problem. Architectures like x86 or arm64 or s390 both have this
similar code. I guess x86 is the first one.

>> diff --git a/arch/powerpc/kernel/machine_kexec.c b/arch/powerpc/kernel/machine_kexec.c
>> index c4ed328a7b96..078fe3d76feb 100644
>> --- a/arch/powerpc/kernel/machine_kexec.c
>> +++ b/arch/powerpc/kernel/machine_kexec.c
>> @@ -86,6 +86,7 @@ void arch_crash_save_vmcoreinfo(void)
>>   	VMCOREINFO_STRUCT_SIZE(mmu_psize_def);
>>   	VMCOREINFO_OFFSET(mmu_psize_def, shift);
>>   #endif
>> +	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
>>   }
> 
> There's no mention of that in the commit log.
> 
> Please split it into a separate patch and describe what you're doing and
> why.

OK

> 
>> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
>> index 1f8db666468d..064075f02837 100644
>> --- a/arch/powerpc/kernel/setup-common.c
>> +++ b/arch/powerpc/kernel/setup-common.c
>> @@ -715,12 +715,31 @@ static struct notifier_block ppc_panic_block = {
>>   	.priority = INT_MIN /* may not return; must be done last */
>>   };
>>   
>> +/*
>> + * Dump out kernel offset information on panic.
>> + */
>> +static int dump_kernel_offset(struct notifier_block *self, unsigned long v,
>> +			      void *p)
>> +{
>> +	pr_emerg("Kernel Offset: 0x%lx from 0x%lx\n",
>> +		 kaslr_offset(), KERNELBASE);
>> +
>> +	return 0;
>> +}
>> +
>> +static struct notifier_block kernel_offset_notifier = {
>> +	.notifier_call = dump_kernel_offset
>> +};
>> +
>>   void __init setup_panic(void)
>>   {
>>   	/* PPC64 always does a hard irq disable in its panic handler */
>>   	if (!IS_ENABLED(CONFIG_PPC64) && !ppc_md.panic)
>>   		return;
>>   	atomic_notifier_chain_register(&panic_notifier_list, &ppc_panic_block);
> 
>> +	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && kaslr_offset() > 0)
>> +		atomic_notifier_chain_register(&panic_notifier_list,
>> +					       &kernel_offset_notifier);
> 
> Don't you want to do that before the return above?
> 

Eagle eye. This should not affected by the conditions above.

>>   }
> 
> cheers
> 
> .
>