linux-kernel - Re: [PATCH] s390/crash: Fix KEXEC_NOTE

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Date:   Thu, 22 Jun 2017 17:12:07 +0800
From:   Xunlei Pang <xpang@...hat.com>
To:     Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
        Xunlei Pang <xlpang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        akpm@...ux-foundation.org, Eric Biederman <ebiederm@...ssion.com>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        linux-s390@...r.kernel.org, Dave Anderson <anderson@...hat.com>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Gustavo Luiz Duarte <gustavold@...ux.vnet.ibm.com>,
        Mikhail Zaslonko <zaslonko@...ux.vnet.ibm.com>
Subject: Re: [PATCH] s390/crash: Fix KEXEC_NOTE_BYTES definition

On 06/22/2017 at 01:44 AM, Michael Holzheu wrote:
> Am Fri,  9 Jun 2017 10:17:05 +0800
> schrieb Xunlei Pang <xlpang@...hat.com>:
>
>> S390 KEXEC_NOTE_BYTES is not used by note_buf_t as before, which
>> is now defined as follows:
>>     typedef u32 note_buf_t[CRASH_CORE_NOTE_BYTES/4];
>> It was changed by the CONFIG_CRASH_CORE feature.
>>
>> This patch gets rid of all the old KEXEC_NOTE_BYTES stuff, and
>> renames KEXEC_NOTE_BYTES to CRASH_CORE_NOTE_BYTES for S390.
>>
>> Fixes: 692f66f26a4c ("crash: move crashkernel parsing and vmcore related code under CONFIG_CRASH_CORE")
>> Cc: Dave Young <dyoung@...hat.com>
>> Cc: Dave Anderson <anderson@...hat.com>
>> Cc: Hari Bathini <hbathini@...ux.vnet.ibm.com>
>> Cc: Gustavo Luiz Duarte <gustavold@...ux.vnet.ibm.com>
>> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
> Hello Xunlei,
>
> As you already know on s390 we create the ELF header in the new kernel.
> Therefore we don't use the per-cpu buffers for ELF notes to store
> the register state.
>
> For RHEL7 we still store the registers in machine_kexec.c:add_elf_notes().
> Though we also use the ELF header from new kernel ...
>
> We assume your original problem with the "kmem -s" failure
> was caused by the memory overwrite due to the invalid size of the
> "crash_notes" per-cpu buffers.
>
> Therefore your patch looks good for RHEL7 but for upstream we propose the
> patch below.

Hi Michael,

Yes, we already did this way.
Thanks for the confirmation, the patch below looks good to me.

Regards,
Xunlei

> ---
> [PATCH] s390/crash: Remove unused KEXEC_NOTE_BYTES
>
> After commmit 692f66f26a4c19 ("crash: move crashkernel parsing and vmcore
> related code under CONFIG_CRASH_CORE") the KEXEC_NOTE_BYTES macro is not
> used anymore and for s390 we create the ELF header in the new kernel
> anyway. Therefore remove the macro.
>
> Reported-by: Xunlei Pang <xpang@...hat.com>
> Reviewed-by: Mikhail Zaslonko <zaslonko@...ux.vnet.ibm.com>
> Signed-off-by: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
> ---
>  arch/s390/include/asm/kexec.h | 18 ------------------
>  include/linux/crash_core.h    |  5 +++++
>  include/linux/kexec.h         |  9 ---------
>  3 files changed, 5 insertions(+), 27 deletions(-)
>
> diff --git a/arch/s390/include/asm/kexec.h b/arch/s390/include/asm/kexec.h
> index 2f924bc30e35..dccf24ee26d3 100644
> --- a/arch/s390/include/asm/kexec.h
> +++ b/arch/s390/include/asm/kexec.h
> @@ -41,24 +41,6 @@
>  /* The native architecture */
>  #define KEXEC_ARCH KEXEC_ARCH_S390
>  
> -/*
> - * Size for s390x ELF notes per CPU
> - *
> - * Seven notes plus zero note at the end: prstatus, fpregset, timer,
> - * tod_cmp, tod_reg, control regs, and prefix
> - */
> -#define KEXEC_NOTE_BYTES \
> -	(ALIGN(sizeof(struct elf_note), 4) * 8 + \
> -	 ALIGN(sizeof("CORE"), 4) * 7 + \
> -	 ALIGN(sizeof(struct elf_prstatus), 4) + \
> -	 ALIGN(sizeof(elf_fpregset_t), 4) + \
> -	 ALIGN(sizeof(u64), 4) + \
> -	 ALIGN(sizeof(u64), 4) + \
> -	 ALIGN(sizeof(u32), 4) + \
> -	 ALIGN(sizeof(u64) * 16, 4) + \
> -	 ALIGN(sizeof(u32), 4) \
> -	)
> -
>  /* Provide a dummy definition to avoid build failures. */
>  static inline void crash_setup_regs(struct pt_regs *newregs,
>  					struct pt_regs *oldregs) { }
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index 541a197ba4a2..4090a42578a8 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -10,6 +10,11 @@
>  #define CRASH_CORE_NOTE_NAME_BYTES ALIGN(sizeof(CRASH_CORE_NOTE_NAME), 4)
>  #define CRASH_CORE_NOTE_DESC_BYTES ALIGN(sizeof(struct elf_prstatus), 4)
>  
> +/*
> + * The per-cpu notes area is a list of notes terminated by a "NULL"
> + * note header.  For kdump, the code in vmcore.c runs in the context
> + * of the second kernel to combine them into one note.
> + */
>  #define CRASH_CORE_NOTE_BYTES	   ((CRASH_CORE_NOTE_HEAD_BYTES * 2) +	\
>  				     CRASH_CORE_NOTE_NAME_BYTES +	\
>  				     CRASH_CORE_NOTE_DESC_BYTES)
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index c9481ebcbc0c..65888418fb69 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -63,15 +63,6 @@
>  #define KEXEC_CORE_NOTE_NAME	CRASH_CORE_NOTE_NAME
>  
>  /*
> - * The per-cpu notes area is a list of notes terminated by a "NULL"
> - * note header.  For kdump, the code in vmcore.c runs in the context
> - * of the second kernel to combine them into one note.
> - */
> -#ifndef KEXEC_NOTE_BYTES
> -#define KEXEC_NOTE_BYTES	CRASH_CORE_NOTE_BYTES
> -#endif
> -
> -/*
>   * This structure is used to hold the arguments that are used when loading
>   * kernel binaries.
>   */