linux-kernel - Re: [PATCH v5 10/10] powerpc/fsl_booke/kaslr: dump out kernel offset information on panic

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Message-ID: <87zhklt9eg.fsf@concordia.ellerman.id.au>
Date:   Wed, 07 Aug 2019 23:03:35 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Jason Yan <yanaijie@...wei.com>, 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, wangkefeng.wang@...wei.com,
        yebin10@...wei.com, thunder.leizhen@...wei.com,
        jingxiangfeng@...wei.com, fanchengyang@...wei.com,
        zhaohongjiang@...wei.com, Jason Yan <yanaijie@...wei.com>
Subject: Re: [PATCH v5 10/10] powerpc/fsl_booke/kaslr: dump out kernel offset information on panic

Jason Yan <yanaijie@...wei.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.

> 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.

> 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?

>  }

cheers