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Message-ID: <599f9ff9-9799-b57e-4c88-cf9c60b94a46@huawei.com>
Date: Mon, 29 Jul 2019 22:08:30 +0800
From: Jason Yan <yanaijie@...wei.com>
To: Christophe Leroy <christophe.leroy@....fr>, <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>
CC: <linux-kernel@...r.kernel.org>, <wangkefeng.wang@...wei.com>,
<yebin10@...wei.com>, <thunder.leizhen@...wei.com>,
<jingxiangfeng@...wei.com>, <fanchengyang@...wei.com>
Subject: Re: [RFC PATCH 10/10] powerpc/fsl_booke/kaslr: dump out kernel offset
information on panic
On 2019/7/29 19:43, Christophe Leroy wrote:
>
>
> Le 17/07/2019 à 10:06, Jason Yan a écrit :
>> 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.
>>
>> 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>
>> ---
>> arch/powerpc/include/asm/page.h | 5 +++++
>> arch/powerpc/kernel/machine_kexec.c | 1 +
>> arch/powerpc/kernel/setup-common.c | 23 +++++++++++++++++++++++
>> 3 files changed, 29 insertions(+)
>>
>> diff --git a/arch/powerpc/include/asm/page.h
>> b/arch/powerpc/include/asm/page.h
>> index 60a68d3a54b1..cd3ac530e58d 100644
>> --- a/arch/powerpc/include/asm/page.h
>> +++ b/arch/powerpc/include/asm/page.h
>> @@ -317,6 +317,11 @@ struct vm_area_struct;
>> extern unsigned long kimage_vaddr;
>> +static inline unsigned long kaslr_offset(void)
>> +{
>> + return kimage_vaddr - KERNELBASE;
>> +}
>> +
>> #include <asm-generic/memory_model.h>
>> #endif /* __ASSEMBLY__ */
>> #include <asm/slice.h>
>> 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());
>> }
>> /*
>> diff --git a/arch/powerpc/kernel/setup-common.c
>> b/arch/powerpc/kernel/setup-common.c
>> index 1f8db666468d..49e540c0adeb 100644
>> --- a/arch/powerpc/kernel/setup-common.c
>> +++ b/arch/powerpc/kernel/setup-common.c
>> @@ -715,12 +715,35 @@ 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)
>> +{
>> + const unsigned long offset = kaslr_offset();
>> +
>> + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && offset > 0)
>> + pr_emerg("Kernel Offset: 0x%lx from 0x%lx\n",
>> + offset, KERNELBASE);
>> + else
>> + pr_emerg("Kernel Offset: disabled\n");
>
> Do we really need that else branch ?
>
> Why not just make the below atomic_notifier_chain_register()
> conditionnal to IS_ENABLED(CONFIG_RANDOMIZE_BASE) && offset > 0
> and not print anything otherwise ?
>
I'm trying to keep the same fashion as x86/arm64 do. But I agree
with you that it's simpler to not print anything else if not randomized.
> Christophe
>
>> +
>> + 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);
>> + atomic_notifier_chain_register(&panic_notifier_list,
>> + &kernel_offset_notifier);
>> }
>> #ifdef CONFIG_CHECK_CACHE_COHERENCY
>>
>
> .
>
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