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Date:   Fri, 28 Sep 2018 15:15:54 +0200
From:   Borislav Petkov <bp@suse.de>
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     linux-kernel@vger.kernel.org, Lianbo Jiang <lijiang@redhat.com>,
        Vivek Goyal <vgoyal@redhat.com>, kexec@lists.infradead.org,
        tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
        x86@kernel.org, akpm@linux-foundation.org,
        dan.j.williams@intel.com, thomas.lendacky@amd.com,
        baiyaowei@cmss.chinamobile.com, tiwai@suse.de,
        brijesh.singh@amd.com, dyoung@redhat.com, bhe@redhat.com
Subject: Re: [PATCH 1/3] x86/kexec: Correct KEXEC_BACKUP_SRC_END off-by-one
 error
Message-ID: <20180928131554.GC21895@zn.tnic>
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On Thu, Sep 27, 2018 at 09:21:55AM -0500, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> The only use of KEXEC_BACKUP_SRC_END is as an argument to
> walk_system_ram_res():
> 
>   int crash_load_segments(struct kimage *image)
>   {
>     ...
>     walk_system_ram_res(KEXEC_BACKUP_SRC_START, KEXEC_BACKUP_SRC_END,
>                         image, determine_backup_region);
> 
> walk_system_ram_res() expects "start, end" arguments that are inclusive,
> i.e., the range to be walked includes both the start and end addresses.
> 
> KEXEC_BACKUP_SRC_END was previously defined as (640 * 1024UL), which is the
> first address *past* the desired 0-640KB range.
> 
> Define KEXEC_BACKUP_SRC_END as (640 * 1024UL - 1) so the KEXEC_BACKUP_SRC
> region is [0-0x9ffff], not [0-0xa0000].
> 
> Fixes: dd5f726076cc ("kexec: support for kexec on panic using new system call")
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
>  arch/x86/include/asm/kexec.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
> index f327236f0fa7..5125fca472bb 100644
> --- a/arch/x86/include/asm/kexec.h
> +++ b/arch/x86/include/asm/kexec.h
> @@ -67,7 +67,7 @@ struct kimage;
>  
>  /* Memory to backup during crash kdump */
>  #define KEXEC_BACKUP_SRC_START	(0UL)
> -#define KEXEC_BACKUP_SRC_END	(640 * 1024UL)	/* 640K */
> +#define KEXEC_BACKUP_SRC_END	(640 * 1024UL - 1)	/* 640K */
>  
>  /*
>   * CPU does not save ss and sp on stack if execution is already

Reviewed-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)